I agree to inform Dr. Ian Howat if this dataset is to be presented in any publication, presentation or proceeding and to acknowledge the Byrd Polar Research Center (BPRC) Glacier Dynamics Research Group, Ohio State University by name in presentations and publications arising from use of these data.http://www.pgc.umn.edu/elevation/stereo (http://www.pgc.umn.edu/elevation/stereo)
Year 2014 comes in above average for the amount of melting from the Greenland Ice Sheet in the period since 2002. On the other hand, Arctic sea ice was strengthened in 2014.
The most important results of climate
monitoring in the Arctic in 2014 are:
• The Greenland Ice Sheet contributed
approximately 1.2 mm to sea-level rise;
• Below average reflection of sunlight is
associated with increased melting from the
Greenland Ice Sheet in 2014;
• The surface mass balance of the Greenland
Ice Sheet was lower than normal, but not
record low;
• Arctic sea ice strengthened in 2014;
• A new temperature record was established
in west Greenland in June 2014;
• There were no exceptional changes in the
movements of glacier fronts in Greenland.
Zachariae Glacier is one of the 20 largest
glaciers that changed the most during the 2014
melt season. Already in April several km2 had
broken off the terminus, but were nonetheless
partially rebuilt by the glacier flow from the ice
sheet. However, between July and August an
additional roughly 20 km2 of the glacier’s
terminus was broken off to form floating
icebergs. This especially affected the central
and northern parts of the glacier, which lost 4
km between June and September.
Even though there were no major changes in
the terminus of 79N Glacier, there were both
more and larger meltwater lakes on the surface
of the glacier in the middle of August in
comparison with the same period in 2013.
Abstract. This study presents average velocity fields, mass flux estimates and central flowline profiles for five major Greenland outlet glaciers; Jakobshavn Isbræ, Nioghalvfjerdsbræ, Kangerdlugssuaq, Helheim and Petermann glaciers, spanning the period (August) 2013–(September) 2014. The results are produced by the feature tracking toolbox, ImGRAFT using Landsat-8, panchromatic data. The resulting velocity fields agree with the findings of existing studies. Furthermore, our results show an unprecedented speed of over 50 m day−1 at Jakobshavn Isbræ as it continues to retreat. All the processed data will be freely available for download at http://imgraft.glaciology.net (http://imgraft.glaciology.net).
ImGRAFT is (unfortunately for me) written in matlab, otherwise I would love to apply it at Zachariae.You might email the authors and ask them to please run your favorite pair of Zachariae Landsat-8's (matched viewing geometry, minimal clouds, id numbers like LC80090112014040LGN00 supplied). Explain that you plan to write a blog article on Zachariae citing their software. Myself, I hope they start to offer this as an online service (like the 301 G'Mac filters), running matlab in the background.
Our data indicate yet a further speedup of Jakobshavn Isbræ in July 2014 peaking at a record 52 meters per day. This was manually verified using a simple triangulation of selected features near the terminus ... The current flux gate at the grounding line for Jakobshavn Isbræ sees ~30 cubic km per year go by... Joughin 2014 suggest that a tenfold increase in this estimate in the future is plausible..
A noticeable observation at Petermann is the distinct separation between the main trunk and the northern marginal slower flow which has been described in Münchow 2014. The large tributary that flows into the main glacier forms a slower flowing part of the glacier tongue. Petermann and Nioghalvfjerdsbræ display highest speeds not at the terminus but at approximately 45 and 70 km from the calving front respectively
With incredible resolution comes incredible file sizes ... hopefully we little desktops can stay in the game.Improving ground resolution is very important to more reliable modelling of the Greenland Ice Sheet -- but file sizes go as the square (from 5km --> 1 km is 25x the pixels). A time series of Landsat-8s is already a full plate; the new SETSM DEM is 10 GB per tile x 2300 tiles.
Might try matLab in OctaveInteresting suggestion, sidd. Octave just thinks of images as matrices, stacked one per color channel. This makes sense as a lot of raster image processing amounts to very basic matrix manipulations. As mentioned before, the BMP file format interconverts image display on the monitor with its numerical matrix equivalent. Octave now has a GUI to get out of command line; I haven' tried it.
report from Denmark polar portal does not agree with NSIDC which shows only 6 Gton for 2013-2014 mass loss from GRACE data.Indeed, something is not right here. The polar portal offers an explanation in Box 2, page 3: power was shut off to the GRACE satellite in July to spare the battery which couldn't have come at worse time for Greenland mass balance. I'm inclined to go with the graph in Fig.3 below. The pdf also has a good summary of weather aspects.
Satellite observations since 2002 show that the Greenland Ice Sheet is not in balance and that the loss of ice from calving of icebergs and surface melting exceeds the overall mass input from snowfall. The Greenland Ice Sheet has lost about 250 Gt/year of mass over the past decade. One Gt is 1 billion tonnes and is equivalent to 1 cubic kilometer of water. A loss of mass of 100 Gt of ice corresponds to a sea level rise of 0.28 mm.http://polarportal.dk/fileadmin/user_upload/PolarPortal/season_report_2014/PolarPortal2014-EN.pdf (http://polarportal.dk/fileadmin/user_upload/PolarPortal/season_report_2014/PolarPortal2014-EN.pdf)
The annual melting season is normally at its peak in July or at the beginning of August, and 2014 was a year with greater melting than normal—although less than the highest level so far, 2012. According to our reflectivity based estimate, the ice sheet lost mass equivalent to approximately 1.7 mm sea-‐level rise during the period of greatest sunlight from May to September 2014.
This is about 50% more than the average for the years 2002 to 2013 and only about 5% less than the loss of mass in the record year 2012. This loss of mass puts the year 2014 in third place in relation to melting since 2002. Second place is year 2010. When the average addition of mass equivalent to 0.4 mm during the winter period from October to March is considered, it is estimated that in 2014 the Greenland Ice Sheet contributed about 1.2 mm to sea-‐level rise over the entire period.
Changes in the overall mass of the ice sheet are determined by two different methods. One method builds on measurements from the GRACE satellite of changes in the gravitational pull of the ice sheet, which decreases when there is less ice. However, it takes up to two to three months to analyze these data and GRACE data are unavailable mid-‐2014 due to satellite power problems.
Therefore, researchers from GEUS have developed a supplementary method that is faster but not quite as precise as measurements of the gravity. This method is based on measurements of the albedo effect, that is, the reflection of sunlight from the ice sheet. This can be used because a statistical relationship has been found between the albedo effect and the gravity of the ice sheet. In this way a rapid, but provisional assessment can be made of the loss of mass from the ice sheet, while the more precise data are being analyzed.
C21B-0329 Firn and percolation conditions in the vicinity of recently formed high elevation supra-glacial lakes on the Greenland Ice Sheet assessed by airborne radar
ePoster - https://agu.confex.com/data/handout/agu/fm14/Paper_24929_handout_1496_0.pdf
The western region of the Greenland Ice Sheet around and above the equilibrium line is characterized by relatively high accumulation rates with short-lasting melt events of variable intensity during the summer months. During melt season, supra-glacial lakes are formed at least temporarily in depressions found in the topography of the ice.
These ponds can form and drain rapidly, affecting the dynamics of the ice below. Recent warming trends have gradually increased the amount of meltwater found every summer over the ice sheet, with melt regimes migrating to higher altitudes. Consequentially, supra-glacial lakes are being found at higher elevations, yet it is unclear what mechanisms control their formation over firn.
We used data from different radar systems acquired by Operation Icebridge around and over lakes formed above the equilibrium line of the Greenland Ice Sheet to study internal features of identified frozen/drained supra-glacial lakes, and to investigate near-surface snow and firn conditions in the vicinity of the ponds by radar-mapping internal snowpack structure. Airborne radar and additional field observations revealed extensive and impermeable ice layers 20-70 cm thick formed at elevations between 1500 m and 2200 m.
Buried by winter accumulation, these ice layers prevent further meltwater to percolate deeper during melt season, limiting firn capacity to absorb meltwater and causing near-surface snowpack saturation, thus facilitating the transport of meltwater to newly-formed basins above the equilibrium line. Ice penetrating capabilities from the different radar systems allow the survey of different firn layers and internal features created by refrozen meltwater. IceBridge data is acquired in early spring, when no liquid water content is found over this region ensuring adequate radar response.
C21B-0316Massive Perched Ice Layers in the Shallow Firn of Greenland's Lower Accumulation Area Inhibit Percolation and Enhance Runoff
ePoster - https://agu.confex.com/data/handout/agu/fm14/Paper_10527_handout_506_0.pdf
Greenland's recent trend of record-breaking melt seasons (2012, 2010, 2007, 2002, et al.) have substantially increased the amount of melt water generated in the ice sheet's lower accumulation area. Due to this enhanced refreezing in the firn, regions with low accumulation rates have formed multi-annual ice layers 5-10+ meters thick in the thermally active shallow firn that overlies porous firn at depth.
The loss of pore space in the firn prevents the majority of melt water from percolating to depth and results in surface runoff where water previously would have refrozen. Here we present evidence from in situ ground-penetrating radar, firn cores and airborne radar from NASA's Operation IceBridge, collected both before and after Greenland's 2012 melt season, to illustrate the mechanism by which southwest Greenland's runoff zone in 2012 extended 20 kilometers inland from the long-term saturation line.
Additional evidence from satellite imagery, firn temperature profiles and modeling support the notion that these layers blocked percolation and contributed to Greenland's record runoff in 2012. Should Greenland's trend of anomalously warm summers persist, these massive lenses are likely to grow thicker and extend further inland, resulting in enhanced runoff and rapid upslope migration of the equilibrium line. These results illustrate the vital importance of understanding subsurface firn changes in order to accurately predict Greenland's future runoff in a changing climate.
Nice! It would take n well-distributed rocks to really rectify image geometry (ImageJ2 distortion plugin) -- even when orbital parameters are 'known' they have too much uncertainty for geodesy (Howat 2014).
In particular for interferometry, SENTINEL-1 requires stringent orbit control. Satellite positioning along the orbit must be accurate, with pointing and timing/synchronisation between interferometric pairs. Orbit positioning control for SENTINEL-1 is defined using an orbital Earth fixed "tube", 50 m (RMS) wide in radius, around a nominal operational path. The satellite is kept inside this "tube" for most of its operational lifetime.
The ImGRAFT output is an evenly gridded vector field yet it can only find corresponding features in the two images here and there. Can it also output just the primary match arrows it uses to make the grid? Can it output RGB where as HSV the V is velocity magnitude and H is 360º direction? With 3 successive image dates, can it display acceleration dv/dt?
Everything else is add-on: the evenly grid, the output image with colors and arrows. The user can change those as long as it is programmable. nothing in the software is aware displacements are a (u,v) vector field with dictated by physics)This modularity is a good thing ... users can build various paths through various options for interpolation and display in something like a PENTAHO drag'n'drop environment. Whether you end up with something the corresponds to reality as well as interferometric SAR (which inherently provides continuous velocity contours) isn't frequently validated on the ground (eg fiberglass pole array to 80 m depth Swiss Camp flow line).
The ImGRAFT software contains a module "camera.m" that can rectify for differences in cameras (focal length, distortions) and positions. They don't use it on the Landsat images though, neither do I.The Landsat-8 has a group of image geometric attributes, things like ROLL_ANGLE = -0.001 which I've never seen vary to any interesting extent.
Surface Extraction with TIN-based Search-space Minimization (SETSM)The interometric velocity below is adapted from http://posters.unh.edu/gallery/view/3177/ (http://posters.unh.edu/gallery/view/3177/) "Investigating the cause of the 2012 Acceleration of Jakobshavn Isbrae, Greenland Using High Resolution Observations of the Glacier Terminus" by Ryan Cassotto
Fully automatic stereo-photogrammetric Digital Elevation Model (DEM) extraction from pushbroom satellite imagery
Since the geolocation accuracy of RPCs without ground control for WorldView-1 and 2 is 5m CE90 (DigitalGlobe, 2013), there is an offset between corresponding points projected by the vertical line locus. Where large enough, this offset can result in matching failure. Relative RPC updating provides an adaptive method for mitigating this error.
For any RPC-constrained DEM extraction algorithm there will be two common and dominant sources of error: blunders and RPC errors. Blunders are caused by incorrect matching of features between images, resulting in surface outliers. The iterative restriction of the search area in SETSM, as well as the blunder detection algorithm in step 4 above, substantially reduce blunders.
RPC errors are typically the result of errors in satellite positioning and look geometry, increasing with sensor look angle. These errors have two main effects: First, they result in misalignment of the stereo pair in the matching routine, resulting in poor match returns, which is mitigated in SETSM through iterative refinement of the search space.
The second effect is a bias in DEM elevations. Cheng and Chappel (2008), found an average bias of 5 m in several test DEMS extracted from WorldView-1 imagery. We are still testing for this bias using both Worldview 1 and 2 image pairs ... We anticipate further accuracy gains by determining which look geometries result in the best RCP determinations. The most effective way to reduce geometrically induced error, however, is by using ground control points (GCP).
... if the center of the displacement vector is used versus the vector tail (starting center point of the source sub-scene), here glaciers flow a kilometer between image pairs – enough so that the strain field traversed by the tracked features becomes important.Meanwhile, never mind this vector cross-correlation software, here is NASA printing out DEM slope vectors and drawing drainage divides by hand, then re-digitizing: http://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php (http://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php)
On errors, a single value of ±2 m/d is used, for the 16-day repeat pairs using the same path-row, a systematic error based on geo-location issues. However, adjacent (non- identical) path-rows were used, with time-separations varying quite a bit. The greater error with non-identical viewing geometry is mentioned, but without elaboration.
Error bars need to be shown in Figure 2 - and this will show that 2m/d error will blur quite a bit of the seasonal signal you appear to be mapping. Also show the seasonal variation relative to the merged mean Landsat 8 velocity or to the InSAR mean. But this will point out uncorrected errors in the Landsat 8 mapping.
Figure 2: should really re-design Fig2 for Niog and Petermann – there’s no detail visible, and a lot of white space.
On Figure 1, are the centerlines correct? picking centerlines with some of the data having systematic errors in flow direction is risky. The centerline for Niog seems off? it appears as though nunataks are sitting within the ice stream.
Results are like those already reported with the exception of the slightly greater flow speed for Jacobshavn (±2m/d makes this suspect). How about differencing the new map with the InSAR data -- it would reveal errors, but might reveal evolution.
Drainage divides were digitized using ArcGIS v 9.3. For the majority of the divides, the digitization was done from paper maps of the slope vectors via an Altek Datatab Pro Line puck digitizer. However, in regions where the slope vectors did not yield useful information, imagery was used as a guide. Vector maps showing the downslope maximum-gradient direction were generated from this DEM.
Drainage system divides were drawn on these maps, primary divides along major ridges, and secondary divides starting at points of interest, drawn upslope until meeting a primary divide or another secondary divide. The drainage systems and sub-systems include all basins and sub-basins in each.
The drainage system outlines used here are defined in WGS84 coordinates. This was ignored in this work, and the coordinates were treated as if they were Topex coordinates. The maximum difference between Topex and WGS84 latitude occurs at a latitude of 45° and is approximately 1.37 cm.
Models of Greenland Ice Melting Could Be Way Low
Nukefix writes, Hmmm box-plots still for SMB, I think more research is needed to produce plots with mass-balance each year.I chased down where this all stood back in 1998-2001. As it happens, B Csatho, the lead author of the PNAS paper above co-authored three earlier versions of Greenland surface mass balance:
however, my gut feeling tells me something big is on -- though it might just be those JägermeistersBelow is a crumpled handout that supposedly a janitor picked up after a secretive closed-door AGU14 session that predicts something big going on at Zachariae ... can you make out what it is saying???
Temperature and velocity profiles inferred by thermal flowline modeling for high elevation regions of the Greenland Ice Sheet
AN Sommers, H Rajaram, WT Colgan
http://hydrosciences.colorado.edu/symposium/abstract_details.php?abstract_id=7 (http://hydrosciences.colorado.edu/symposium/abstract_details.php?abstract_id=7)
...Most recent changes in the surface mass balance and ice dynamics of the Greenland ice sheet have been restricted to elevations below 2,000m. Substantial computational efficiency can be gained by limiting numerical modeling efforts to this lower elevation periphery, where changes in ice sheet form and flow are most pronounced, rather than modeling the entire ice sheet from the main divide to the margin. Accurately modeling the lower elevations with this approach is dependent on prescribing accurate velocity and temperature profiles at the upstream boundary... Without corresponding velocity and temperature profiles, however, these data alone are insufficient to serve as upstream boundary conditions for lower elevation thermo-mechanical modeling.
Using a two-dimensional, enthalpy-based thermal flowline model, we generate velocity and temperature profiles across the ice sheet depth at the PARCA stake locations. While prescribing ice surface and bedrock elevation, observed surface velocities at the stake locations and the ice discharge calculated from surface mass balance serve as modeling targets. We employ an iterative procedure between mechanical and thermal calculations; ice velocities found by solving the momentum equation (via the Shallow Ice Approximation, which is valid for these high-elevation domains) inform the energy equation to solve for temperature and liquid water content, which then inform the velocity calculations, and so on until convergence.
Preliminary results suggest that observed surface velocities in some regions of Greenland can only be reproduced with a temperate bed at high elevations...
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This convergence term represents an important 3-D effect, ensures that mass balance is maintained throughout the model domain, and allows for realistic evolution of mass and momentum near the terminus. We note that this prescribed flux convergence differs from implementation of flow convergence in earlier work with flow line models, where the additional mass is added as an input to the surface mass balance. Although the latter will result in correct flux, it neglects the direct effect of the additional flux on the velocity field and may consequently underestimate velocity change while overestimating elevation change.
2015 will be the year of foliations, principal curvatures and moving Darboux framesHolla! Differential geometers to Greenland! While I'm not into data crunching, I'd love to see some details of this real application of diff. geometry.
Differential geometers to Greenland! While I'm not into data crunching, I'd love real application of diff. geometry.Martin, that's fantastic to hear some interest in this! A day or two delay before I can back to you on melt and sea level rise.
New paper by Smith et a 2015 on Greenland drainage:Video interview and some spectacular scenes from 2012 melt: http://www.latimes.com/science/sciencenow/la-sci-sn-catastrophic-greenland-melt-20150112-story.html (http://www.latimes.com/science/sciencenow/la-sci-sn-catastrophic-greenland-melt-20150112-story.html)
http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html (http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html)
Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056–0.112 km3⋅d−1 vs. ∼0.103 km3⋅d−1), and when integrated over the melt season, totaled just 37–75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.Open question: Duration of this
nontrivial subglacial water storage
The mapped river channels only nominally followed topographic relief, often breaching ice divides. Runoff flowing to lower elevations did not first fill topographic depressions, contrary to a key assumption of terrestrial watershed models, that depressions must fill with meltwater before overtopping
Martin writes my main subject of study in the 1990ies was stochastic differential geometry, Brownian motionDid you ever do anything with Ricci flow? It is like the heat equation only for diffusing the metric tensor. I wish there was more 19th century math online -- what was Ricci's physical motivation? Nice treatment at wiki: https://en.wikipedia.org/wiki/Ricci_flow. I have been thinking about the z in ice xyz ... seems like height is a start on a natural metric (leading to driving stress) but then over a 450 km flow line, that subtends quite an angle on S2 so really should be using r. Then the Bouguet gravity varies quite a bit too, so much for a simple ice weight calc.
Thanks for making me feel stupid, guys. ;DI feel the same.
Radiostratigraphy and age structure of the Greenland Ice Sheet
JA MacGregor, MA Fahnestock, GA Catania, JD Paden, S Goginen, SK Young, SC Rybarski, AN Mabrey, BM Wagman, M Morlighem
We present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by U Kansas between 1993 and 2013 [2014 added very little]. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflector slope from the phase recorded by coherent radars. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.
When integrated along-track, these slope fields predict the radiostratigraphy and simplify semi-automatic reflection tracing. The stratigraphy was dated via synchronized depth–age relationships for the six deep Greenland ice cores [Camp Century, NEEM NGRIP, GRIP, GISP2, DYE3].
Additional reflections were dated by matching reflections between transects and by extending depth–age relationships using the local effective vertical strain rate [see http://gravity.ucsd.edu/pub/2004_elsberg.pdf (http://gravity.ucsd.edu/pub/2004_elsberg.pdf)].
The oldest reflectors (Eemian) are found mostly [but not entirely] in the northern part of the ice sheet. Reflections do not conform to the bed topography within the onset regions of fast-flowing outlet glaciers and ice streams. Disrupted radiostratigraphy is also observed in a region north of NEGIS that is not presently flowing rapidly.
Dated reflections are used to make a 3D gridded age product for the ice sheet and to determine the depths of key climate transitions that were not observed directly.
how tectonic motion northward of Greenland set the stage for ice sheet formation
"Peering into the thousands of frozen layers inside Greenland’s ice sheet is like looking back in time. Each layer provides a record of not only snowfall and melting events, but what the Earth’s climate was like at the dawn of civilization, or during the last ice age, or during an ancient period of warmth similar to the one we are experiencing today. Using radar data from NASA’s Operation IceBridge, scientists have built the first-ever comprehensive map of the layers deep inside the ice sheet. This video is public domain and can be downloaded at: http://svs.gsfc.nasa.gov/goto?4249 (http://svs.gsfc.nasa.gov/goto?4249) [dead link]"
Melt extent in Greenland was well above average in 2014, tying for the 7th highest extent in the 35-year satellite record. Overall, climate patterns favored intense west coast and northwest ice sheet melting, with relatively cool conditions in the southeast.
“Prior to this study, a good ice-sheet model was one that got its present thickness and surface speed right. Now, they’ll also be able to work on getting its history right, which is important because ice sheets have very long memories.”http://www.nasa.gov/content/goddard/nasa-data-peers-into-greenlands-ice-sheet/#.VMK3dWTF-QM (http://www.nasa.gov/content/goddard/nasa-data-peers-into-greenlands-ice-sheet/#.VMK3dWTF-QM)
Flying over northern Greenland during the 2011 Ice Bridge season, Kirsty Tinto, a geophysicist at Lamont-Doherty, sat up straight when the radar images began to reveal a deformed layer-cake structure. “When you’re flying over this flat, white landscape people almost fall asleep it’s so boring—layer cake, layer cake, layer cake,” said Tinto, a study coauthor of Bell 2014. “But then suddenly these things appear on the screen. It’s very exciting. You get a sense of these invisible processes happening underneath.”MacGregor's online CV suggests two follow-up papers are coming soon. These had to await prior publication of the isochron database paper under discussion here. If they have actually been able to wring some experimental temperature data out of the radar archive, that would be huge news. MacGregor has 5 previous publications on englacial radar attenuation, mostly in Antarctica.
Abstract. In a warming climate, surface meltwater production on large ice sheets is expected to increase. If this water is delivered to the ice sheet base it may have important consequences for ice dynamics. For example, basal water distributed in a diffuse network can decrease basal friction and accelerate ice flow whereas channelized basal water can move quickly to the ice margin, where it can alter fjord circulation and submarine melt rates.The first page of the article is offered by readcube, the whole article for $4. Helpfully, supplemental data is free.
Less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets. Here we show that a subglacial lake in Greenland drained quickly, as seen in the collapse of the ice surface, and then refilled from surface meltwater input.
We use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the Flade Isblink ice cap in northeast Greenland [81.3º latitude].
During the autumn of 2011, a collapse basin about 70 meters deep and about 0.4 cubic kilometers in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord. Over the next two years, rapid uplift of the floor of the basin (which is approximately 8.4 square kilometers in area) occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake.
Our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet. Sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice and alter downstream ice dynamics. Heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate.
North Atlantic area experienced a series of dramatic climatic fluctuations known as Dansgaard-Oeschger events, during which oceanic and atmospheric conditions alternated between full glacial (stadial) and relatively mild (interstadial) conditions. Ice-core records resolve the most recent of the D-O events in sub-annual detail, and analysis of these high-resolution records suggests that fundamental atmospheric circulation changes took place in just a few years.
About 25 abrupt transitions from stadial to interstadial conditions took place during the Last Glacial period and these vary in amplitude from 5ºC to 16ºC, each completed within a few decades. The interstadials vary in duration from around a century to many millennia, with surface air temperature (as reflected in d18O values) decreasing gradually before each interstadial ended in a less pronounced but nevertheless abrupt transition to stadial conditions. The alternating pattern of stadials and interstadials is reflected in many different palaeoclimatic records from diverse archives, but is particularly clear in the Greenland ice-core records.
A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25e45 ka b2kI wondered how they could determine that it all came from Iceland (and indeed which volcano there) rather than some big stratovolcano far far away. The answer is plotting ash composition in spaces that resolve the potential sources.
Quaternary Science Reviews
AJ Bourne 2014
http://dx.doi.org/10.1016/j.quascirev.2014.07.017 (http://dx.doi.org/10.1016/j.quascirev.2014.07.017)
Tephra layers preserved within the Greenland ice-cores are crucial for the independent synchronisation of these high-resolution records to other palaeoclimatic archives. Here we present a new and detailed tephrochronological framework for the time period 25,000-45,000 a b2k that brings together results from 4 deep Greenland ice-cores.
In total, 99 tephra deposits, the majority of which are preserved as cryptotephra, are described from the NGRIP, NEEM, GRIP and DYE-3 records. The major element signatures of single glass shards within these deposits indicate that 93 are basaltic in composition all originating from Iceland.
Specifically, 43 originate from Grimsvotn, 20 are thought to be sourced from the Katla volcanic system and 17 show affinity to the Kverkfjoll system.
Robust geochemical characterisations, independent ages derived from the GICC05 ice-core chronology, and the stratigraphic positions of these deposits relative to the Dansgaard-Oeschger climate events represent a key framework that provides new information on the frequency and nature of volcanic events in the North Atlantic region between GS-3 and GI-12.
Of particular importance are 19 tephra deposits that lie on the rapid climatic transitions that punctuate the last glacial period. This framework of well-constrained, time-synchronous tie-lines represents an important step towards the independent synchronization of marine, terrestrial and ice-core records from the North Atlantic region, in order to assess the phasing of rapid climatic changes during the last glacial period.
“If we are going to do something to mitigate sea level rise, we need to do it earlier rather than later,” Dr Applegate said. “The longer we wait, the more rapidly the changes will take place and the more difficult it will be to change.”
The model is based on the shallow ice approximation for grounded ice and the shallow shelf approximation for floating ice. It is coded in Fortran 90 and uses finite difference discretisation on a staggered (Arakawa C) grid, the velocity components being taken between grid points. Its particularity is the detailed treatment of basal temperate layers (that is, regions with a temperature at the pressure melting point), which are positioned by fulfilling a Stefan-type jump condition at the interface to the cold ice regions. Within the temperate layers, the water content is computed, and its influence on the ice viscosity is taken into account.
| Required model forcing: Surface mass balance (precipitation, evaporation, runoff). Mean annual air temperature above the ice. Eustatic sea level. Geothermal heat flux. | Output (as functions of position and time): Extent and thickness of the ice sheet. Velocity field. Temperature field. Water content field (temperate regions). Age of the ice. Isostatic displacement and temperature of the lithosphere. |
A model explanation may sometimes be illusory; the fact that a model with adjustable parameters gives plausible numerical values does not prove the validity of the underlying assumptions ... use of all the data to 'tune' model parameters precludes a proper assessment of its abilities.
…
"Greenland temperatures are quite strongly related to solar activity," Takuro Kobashi, the lead author of the study and a researcher at the University of Bern, Switzerland, said. They looked at temperature trends over a 2,000 year period and showed that temperatures in Greenland had a negative relationship with solar activity.
…
A public debate between scientists was spurred by findings presented at the Royal Astronomical Society in the United Kingdom by a mathematics professor, Valentina Zharkova, that solar activity will decrease drastically during the 2030s, reaching what is popularly known as the solar minimum.
…
[D]iminishing solar activity could be more worrying, because it would mean that Greenland would heat up more than expected in those years and predictions about the melting of ice sheets may be off the mark. "If predictions about the diminishing solar activity are true, then we can expect the Greenland ice sheet to melt faster as temperatures there remain higher than the average in the Northern Hemisphere," Kobashi said.
...
The abrupt Northern Hemispheric (NH) warming at the end of the 20th century has been attributed to an enhanced greenhouse effect. Yet, Greenland and surrounding subpolar North Atlantic remained anomalously cold in 1970s- early 1990s. Here, we reconstructed robust Greenland temperature records (NGRIP and GISP2) over the past 2100 years using argon and nitrogen isotopes in air trapped within ice cores, and show that this cold anomaly was part of a recursive pattern of antiphase Greenland temperature responses to solar variability with a possible multidecadal lag. We hypothesize that high solar activity during the modern solar maximum (ca. 1950s-1980s) resulted in a cooling over Greenland and surrounding subpolar North Atlantic through the slow-down of Atlantic Meridional Overturning Circulation (AMOC) with atmospheric feedback processes.
The new study concludes that high solar activity starting in the 1950s and continuing through the 1980s played a role in slowing down ocean circulation between the South Atlantic and the North Atlantic oceans. Combined with an influx of fresh water from melting glaciers, this slowdown halted warm water and air from reaching Greenland and cooled the island.http://news.discovery.com/earth/global-warming/weakened-solar-activity-could-speed-up-greenland-ice-melt-150717.htm (http://news.discovery.com/earth/global-warming/weakened-solar-activity-could-speed-up-greenland-ice-melt-150717.htm)
But that mitigation from global warming didn’t last, and it’s actually reversed itself. Conversely, the researchers’ findings also suggest that weak solar activity, as the sun is currently experiencing, could slowly fire up the ocean circulation mechanism, increasing the amount of warm water and air flowing to Greenland. Starting around 2025, temperatures in Greenland could increase more than anticipated and the island’s ice sheet could melt faster than projected.
This unexpected ice loss would compound projected sea-level rise expected to occur as a result of climate change, Kobashi said. The melting Greenland ice sheet accounted for one-third of the rise in global sea level every year from 1992 to 2011.
In any case Applegate et al 2014 found much higher potential ice loss from Greenland:
http://link.springer.com/article/10.1007%2Fs00382-014-2451-7 (http://link.springer.com/article/10.1007%2Fs00382-014-2451-7)
In their supplementary fig1, attached below, all ice from GIS could be gone in as little as 300 yrs under a worst-case high warming scenario (6-8C global warming, 12C warming over GIS; amplification factor 1.5-2.0). This would mean a maximum SLR-contribution from GIS of 2-3m/century.
“No one has ever collected a data set like this,” Asa Rennermalm, a professor of geography at the Rutgers University Climate Institute who was running the project with Dr. Smith, told the team over a lunch of musk ox burgers at the Kangerlussuaq airport cafeteria.
“Collapse of the entire basin is going to take a long time, it’s not going to happen tomorrow,” says Mouginot. “But it’s a process, when you start, it’s like Jakobshavn — [you don’t] see the glacier recovering from that.”
I've created an animation using the IceBridge bedrock data overlaid with the new image of the Sentinel data that A-Team.
Absolutely! Here is one that is under 1MB, so hopefully it will play properly. I have the higher resolution version (and the source file) that I can email if anyone wants to look at them.
Great animation! ;)
Zachariae Fjord will be a serious contender to world largest fjord system title in the future, this now belongs to Scoresby Sund (a bit further south).
Does anyone know if there have been any sea floor cores drilled in Disko Bay? I would not be surprised to learn that there was once a Disko Bay Ice Shelf that was bifurcated around Disko Island like the Ronne-Filchner Ice Shelf in Antarctica, but I'd be interested to see if that has been confirmed scientifically.
6. ConclusionsPicture with locations from Kelley et al attached.
New 10Be ages from around Disko Bugt, western Greenland,
place the deglaciation of western Disko Bugt at 10.8 0.5 ka, with
the ice margin reaching the eastern coast of Disko Bugt near Ilulissat
at 10.1 0.3 ka and in southeastern Disko Bugt at 9.2 0.1 ka.
This chronology yields a retreat rate between w50 and 450 m a1
across central Disko Bugt. This rate indicates that w25% of the
overall retreat between the shelf edge and the current position
occurred in as little as 700 years. We suggest this retreat was the
result of internal ice dynamics acting upon an ice sheet driven out
of equilibrium by climatic factors. These findings further emphasize
the ability of marine sectors of ice sheets to change rapidly due to
ice dynamics in warming climates (e.g. Kjær et al., 2012). Our
chronology fills a gap in the current understanding of the early
Holocene behavior of the GrIS in Disko Bugt, and provides a dataset
that completes a history of a western GrIS margin spanning from
the continental shelf to the present ice position, and from the latest
Pleistocene through the Holocene.
I find it particularly interesting that the NE Greenland Ice Stream moves quickly very near the deep bedrock canyon underlying the Storstrømmen glacier, and then stops. I wish the directional data on the ice movement were preserved, but if the ice is moving toward the canyon and then stopped by the pining of the islands near the calving face, it will be very interesting to see what happens if the calving face retreats northwest slightly.Storströmmen has been slowing down, or at least ice has been piling up there according to altimetry. The Ice Velocity data does contain the direction so I expect it to be there once the S-1 Greenland-product is officially released by the project:
As Arctic Peoples at COP21 in Paris appeal for unity to halt global warming, writes Tim Radford, scientists report that Greenland's glaciers are now melting at a speed not seen since the last Ice Age almost 10,000 years ago.
The glaciers of Greenland are retreating two to three times faster now than at any time since the last Ice Age ended 9,500 years ago, according to new research.
The news comes as indigenous peoples from the northern polar region staged an Arctic Day at the COP21 climate change summit in Paris.
Leaders of Greenland peoples, the Nunavut region of Canada and the Inuit Circumpolar Council appealed to the governments of the world to unite to dramatically reduce greenhouse gas emissions and keep global warming to between 1.5C and 2C.
That is because the Arctic is now warming faster than almost anywhere else on Earth, and both human settlements and natural ecosystems are vulnerable.
That the Greenland glaciers are in retreat is itself not news. Satellite data and measurements on the ground have repeatedly confirmed the retreat of the glaciers, the loss of ice and the acceleration of flow. The Jakobshavn Isbrae glacier has even reached a speed of 17 kilometres a year.
Sediment cores
But US scientists report in Climate of the Past journal that the present rate of loss is without precedent.
They analysed sediment cores from a lake bed fed by two Greenland glaciers and built up a record reaching back nearly 10,000 years, charting the advance and retreat of the ice in response to natural cycles. And they found evidence of climate change triggered by the human combustion of fossil fuels imposed upon the natural pattern.
"Two things are happening", says one of the report's authors, William D'Andrea, a paleoclimatologist at Columbia University's Lamont-Doherty Earth Observatory.
"One is you have a very gradual decrease in the amount of sunlight hitting high latitudes in the summer. If that were the only thing happening, we would expect these glaciers to very slowly be creeping forward, forward, forward.
"But then we come along and start burning fossil fuels and adding carbon dioxide to the atmosphere, and glaciers that would still be growing start to melt back because summer temperatures are warmer."
The evidence lies in the erosion rates revealed by the lake silts. Colder climates mean more ice, which means heavier glaciers, which then grind and erode more rock. Cores of sediment preserve the annual record of seasonal change, and radiocarbon dating techniques can provide a calendar of melting and freezing periods.
The record reveals that erosion decreased 8,500 years ago, increased again, and then around 8,000 years ago the glaciers began almost to waste away. There was very little evidence of erosion, and the lake silt incorporated evidence that plants once bloomed around the lake.
Around 4,000 years ago, the glaciers grew again, and - with intervals of retreat - continued to grow until 100 years ago.
Pattern of retreat
Although the evidence comes from a small area confined to the southeastern part of Greenland, it remains a guide to the bigger picture. The same pattern of advance and retreat is matched by evidence from ocean sediments and cores of ice from Greenland and Baffin Island.
"This shows that there are internal responses within the climate system that can make glaciers grow and shrink on very short timescales", Dr D'Andrea says. "They're really dynamic systems, which we have not had much evidence for prior to this."
Greenland's minister of industry, labour, trade and foreign affairs, Vittus Qujaukitsoq, one the Arctic voices appealing for strong and effective action in Paris, said: "Greenland has an important responsibility in promoting international climate research.
"Greenlandic climate research combines international cutting-edge research with an Arctic human dimension. Our joint Inuit voice and our traditional know-how from across the Arctic should be heard and included in international policy-making."
in many Northern Hemisphere regions glacier advances of the past few hundred years were the most extensive and destroyed the geomorphic evidence of ice growth and retreat during the past several thousand years. Thus, most glacier records have been of limited use for investigating centennial scale climate forcing and feedback mechanisms.
Here we report a continuous record of glacier activity for the last 9.5 ka from southeast Greenland, derived from high-resolution measurements on a proglacial lake sediment sequence. Physical and geochemical parameters show that the glaciers responded to previously documented NH climatic excursions, including the 8.2 ka cooling event, the Holocene Thermal Maximum, Neoglacial cooling, and 20th century warming.
... declining summer insolation caused long-term cooling and glacier expansions during the late Holocene [but] climate system dynamics resulted in repeated episodes of glacier expansion and retreat on multi-decadal to centennial timescales. These episodes coincided with ice rafting events in the North Atlantic Ocean and periods of regional ice cap expansion, which confirms their regional significance and indicates that considerable glacier activity on these timescales is a normal feature of the cryosphere. The data indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the natural range of Holocene variability.
Bedrock erosion at the base of glaciers provides sediment supply for meltwater transport to proglacial lakes. In catchments where other sources of sediment are limited, such as from mass wasting or the release of stored sediment, there is a strong relationship between sediment properties and glacier size; large glaciers produce more minerogenic material than small glaciers. Measurements of physical and geochemical properties of proglacial lake sediments can therefore be used to reconstruct records of past glacier size.
Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century.
We estimate the total ice mass loss and its spatial distribution for three periods: 1900–1983 (75.1 ± 29.4 gigatonnes per year), 1983–2003 (73.8 ± 40.5 gigatonnes per year), and 2003–2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term.
We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years.
Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget
The linked (open access) reference discusses the use of GRACE to evaluate ice flow sensitivity in Greenland to climate change:
Schlegel, N.-J., Wiese, D. N., Larour, E. Y., Watkins, M. M., Box, J. E., Fettweis, X., and van den Broeke, M. R: Application of GRACE to the evaluation of an ice flow model of the Greenland Ice Sheet, The Cryosphere Discuss., doi:10.5194/tc-2015-224, in review, 2016.
AUSTIN, Texas — Scientists have created the first paleo-velocity map that shows how the Greenland Ice Sheet has moved over time, revealing that ice in the interior is moving more slowly toward the edges than it has during the past 9,000 years.
Researchers said the findings don’t change the fact that the ice sheet is losing mass overall and contributing to sea level rise.
Along Greenland’s periphery, many glaciers are rapidly thinning. However, the vast interior of Greenland is slowly thickening.
The authors identified three causes for deceleration. First is that snowfall rates were generally higher during the past 9,000 years, second is the slow stiffening of the ice sheet over time, and third is the collapse of an ice bridge that used to connect Greenland’s ice across the Nares Strait to that of nearby Ellesmere Island. Of most interest were the last two.
“Like many others, I had in mind the ongoing dramatic retreat and speedup along the edges of the ice sheet, so I’d assumed that the interior was faster now too. But it wasn’t,” said MacGregor.
“The ice that formed from snow that fell in Greenland during the last ice age is about three times softer than the ice being formed today,” according to co-author William Colgan.
Because of this difference, the ice sheet is slowly becoming stiffer. As a consequence, the ice sheet is flowing more slowly and getting thicker over time. This effect is most important in southern Greenland, where higher snowfall rates have led to rapid replacement of ice from the last glacial period with more modern Holocene ice.
“But that didn’t explain what was happening elsewhere in Greenland, particularly the northwest, where there isn’t as much snowfall, so the stiffening effect isn’t as important,” said MacGregor.
The explanation of deceleration in the northwest lies in the collapse 10,000 years ago of an “ice bridge” across Nares Strait, which used to connect Greenland’s ice to that on Ellesmere Island. The collapse of the ice bridge at the end of the last ice age led to acceleration in the northwest, but the ice sheet has since returned to a slower pace.
“We’re saying that recent increases in snowfall do not necessarily explain present-day interior thickening,” said Colgan. “If you’re using a satellite altimeter to figure out how much mass Greenland is losing, you’re going to get the answer slightly wrong unless you account for these very long-term signals that are evident in its interior.”
watch JGR for the digest of thermal state of GIS bed, that seems important to understand.Right. That and the status of basal till are the missing pieces. MacGregor 2016 above only went down to the 9000 kyr isochron which might be only the top quarter of ice thickness in central Greenland; MacGregor 2015a had no widespread isochrons to work with below 91 kyr and used a depth-age formula to locate Eemian. That paper deliberately sidestepped Greenland's basal deformations.
MacGregor 2016: The millennial-scale evolution of GrIS rheology can partly explain this response. Ice deposited during the last glacial is approximately three times less viscous (“softer”) than ice deposited during the Holocene1. To explain observations of subtle thickening (1 cm per) at DYE-3, Reeh2 hypothesized that, as softer LGP ice is buried by stiffer Holocene ice, the GrIS interior will thicken (hereafter referred to as “Reeh thickening”).
Reeh thickening is distinct from that induced by increased accumulation rate, decreased rate of firn densification, post LGP isostatic adjustment, or horizontal deceleration due to other poorly constrained mechanisms (e.g., increasing basal friction). By continuity, it follows that this transient viscosity change would also have caused the GrIS interior to decelerate after deglaciation....
Corroborating and expanding upon Reeh’s original hypothesis, we suggest that downward advection of the LGP-Holocene transition partly explains the subtle deceleration we infer in the interior of the southern GrIS. The dynamic consequences of this effect are predicted to have in creased nonlinearly within the GrIS interior during the Holocene and to continue for tens of millennia.
1. Why ice-age ice is sometimes “soft”
WSB Paterson 1991 (doi:10.1016/0165-232X(91)90058-O cited 121 times) full text still paywalled
Data on the mechanical properties, texture, fabric, and impurity content of ice deposited during the last glaciation are reviewed. The conclusions are: (1) Chloride and possibly sulphate ions, in concentrations high relative to those in Holocene ice, impede grain-boundary migration and grain growth so that the crystals remain small. (2) Such ice, in shear parallel to the ice-sheet bed, develops a strong, near-vertical, single-maximum fabric. (3) This fabric favours further deformation and this, in turn, further strengthens the fabric and keeps the crystals small. (4) This is why the strain rate in ice-age ice, in simple shear, is some 2.5 times that in Holocene ice at the same stress and temperature. (5) Ice-age ice under other stress systems, such as ice in roughly the upper 60% of the ice thickness, in bedrock hollows, at a stationary ice divide, in ice streams and in ice shelves, will not have enhanced flow. (6) An anisotropic flow relation must be used for detailed modelling of polar ice sheets.
2. Was the Greenland ice sheet thinner in the late Wisconsinan than now?
Niels Reeh
Nature 317, 797 - 799 (31 October 1985); doi:10.1038/317797a0
http://www.nature.com/nature/journal/v317/n6040/abs/317797a0.html (http://www.nature.com/nature/journal/v317/n6040/abs/317797a0.html) full text still paywalled
Ice of Wisconsinan origin which constitutes the basal layers of the ice caps in arctic Canada and Greenland flows three to four times more readily than the Holocene ice above. A model based on simple ice sheet profile theory is set up for the thickness response of the interior ice sheet regions to the progressive thinning of this soft layer. The model is applied to calculate the thickness response of the Greenland ice sheet at the locations Dye 3 and Crête, and of the Devon Island ice cap in arctic Canada. It is concluded that the mechanism contributes significantly to the thickness change of the Greenland ice sheet, presently at a rate of about 1 cm yr−1 and that this rate of change will persist potentially over thousands of years to come. As regards the Devon Island ice cap, most of the estimated 15% thickness increase has already been accomplished. A further consequence is that in the late Wisconsinan, ice thicknesses of the interior regions of the Greenland ice sheet were likely to have been no greater and possibly even less than at present, in spite of the larger geographical extent of the ice sheet. It is argued that the glacial-interglacial cycles of accumulation rate and ice temperature are likely to enhance this ice thickness variation.
The research, published in the European Geosciences Union journal The Cryosphere, looked at satellite data from 1981 to 2012. The drop in reflectivity from 1996 was probably due to a change in atmospheric circulation that favoured warmer, moist air from the south. The scientists found there was no significant increase in soot from forest fires since 1997 to explain the darkening of the surface.
finally get Sentinel 2igh-res images... Acquisition Plans can be downloaded here:Yes, Sentinel 2 will be a great addition -- some of the longer wavelength bands are more interesting than those of Landsat. We don't know yet how useful these will be on the Greenland ice sheet. The 10 m resolution will also be a big plus for marine terminating glaciers. That link is a big improvement over slow, futile searches at their data portal.
https://sentinel.esa.int/web/sentinel/missions/sentinel-2/acquisition-plans
(The ESA overall is quite hostile to end-user feedback.) I could not imagine worse orbital choices than the ones that they are making available initially. What exactly do they expect to see in early March in the center of the ice sheet with visible and near IR?
Not an April 1 joke: Our new study reveals that under warm and wet conditions, atmospheric heat can melt the lower 1/3 of the Greenland ice sheet more than under sunny conditions. This was especially so during the 2012 heat wave when a record warm North America loaded the air with heat and moisture that drifted to Greenland.
Yeah ESA products are very unfriendly to small end users. I did send them an email suggesting to allow downloads of individual tiles . Most of us are just interested in a few square kilometer and not half of the continent.Just so it is on this thread too, little people can now grab just band 4 (red) with most of the benefit but none of the fou fou. It is 130 MB rather than 8300 MB which is 1.5%. Still, the micro preview is useless and does not indicate if your site is clouded over (scene percent is unsatisfactory). It is truly mystifying why they worry over another 100 KB in a multi GB context.
After much wrestling with their crazy-long file names that should have been in metadata like Landsat, the download drops the scene's date, time and location! So over time you will accumulate many dozen B04.jp2's that you better manually fix at the time of acquisition.Wow. Sounds like Microsofty stone age. What system is doing this?
(...)Seems like classic business administration going on. They can formally work numbers, but lack any understanding. The numbers are in tidy boxes. Outside those boxes the numbers have no dimension, no strategical or any other value. Billions in this box, peanuts in the other. The good German MBA keeps them strictly separate, for anything else would require creative thinking. This is taboo when dealing with money numbers. -- Heck, why a two dollar saddle? Lets do it without because the corresponding box is almost empty. -- I've seen Software sellers trying to do without software engineers.
Around here we say, "you don't put a two dollar saddle on a million dollar mule."
This being Rignot's 4th substantive article for 2016 -- it is a full-time job just reading them.
bigif west greenland slope current is driven north by low presently in Labrador then saturday/sunday we should see a activity glaciers served by a channel out into deeper BaffinGood to get ahead of the curve. A validated prediction carries a lot more weight than a retro-fit.
Global warming is changing the way the Earth wobbles on its polar axis, a new Nasa study has found.
Melting ice sheets, especially in Greenland, are changing the distribution of weight on Earth. And that has caused both the North Pole and the wobble, which is called polar motion, to change course, according to a study published on Friday in the journal Science Advances.
Abstract
Earth’s spin axis has been wandering along the Greenwich meridian since about 2000, representing a 75° eastward shift from its long-term drift direction. The past 115 years have seen unequivocal evidence for a quasi-decadal periodicity, and these motions persist throughout the recent record of pole position, in spite of the new drift direction. We analyze space geodetic and satellite gravimetric data for the period 2003–2015 to show that all of the main features of polar motion are explained by global-scale continent-ocean mass transport. The changes in terrestrial water storage (TWS) and global cryosphere together explain nearly the entire amplitude (83 ± 23%) and mean directional shift (within 5.9° ± 7.6°) of the observed motion. We also find that the TWS variability fully explains the decadal-like changes in polar motion observed during the study period, thus offering a clue to resolving the long-standing quest for determining the origins of decadal oscillations. This newly discovered link between polar motion and global-scale TWS variability has broad implications for the study of past and future climate.
That's amazing, there is rain all other Greenland in the days to come !
Professor Hanna said: "Our research has found an increase in the incidence of high pressure weather systems remaining stationary over Greenland since the 1980s, which is having a significant impact on extreme weather and climate change in the region.http://phys.org/news/2016-04-climate-extreme-weather-linked-high.html (http://phys.org/news/2016-04-climate-extreme-weather-linked-high.html)
These weather systems are occurring in the area more often because of strong Arctic warming and changes in the atmospheric jet stream in recent years.
"This is resulting in an increase in the occurrence of warm air in the region and it is also affecting weather systems downstream of Greenland, such as over the UK. The unusually wet weather seen in the UK in the summers of 2007 and 2012, for instance, is linked to these stationary high pressure systems over Greenland."
The research team, which also includes a climate scientist John Cappelen from the Danish Meteorological Institute in Copenhagen, Denmark, found that Greenland 'blocking' pressure systems have become much more variable from year to year in December in recent decades. This reflects an increasing destabilisation of atmospheric weather systems in late autumn and early winter, which the team believe may be related, at least in part, to dramatic declines in sea-ice coverage in the Arctic region.
"Sea-ice coverage throughout the Arctic has significantly reduced in recent years, which we already know is having an amplifying effect on warming in the region. What this study now tells us is that changes in stationary high pressure over Greenland are adding to the change in polar climate," Professor Hanna added.
Another large and unusually early #Greenland melt is occurring in response to anomalous warmth over the last month
https://twitter.com/zlabe/status/730803456689102848
10 June 18 another melt spike. This year might see 2012 scale melt. http://nsidc.org/greenland-today (http://nsidc.org/greenland-today)To be followed by a plunge on June 16th. I wonder if this will be accompanied by clear skies and sharp S2A images.
omg we have barely wrapped our heads around Sentinel 1A and now they've launched and re-maneuvered its twin Sentinel 2B to the same plane plus taken the first interferograms as of 22 June 2016. The satellites are on the opposite sides of the earth in sun-synchronous near-polar orbits at 693 km altitude with 175 orbits per 12 day repeat.
1B won't be 'commissioned' until mid-September. They may post initial imagery in the meantime so we need to look at the SNAP toolbox to see if it lets the average person make these interferograms (perhaps just using a graph that nukefix could provide), eg for Petermann, Jakobshavn and Pine Island. (Recall we've seen Petermann done in emulation with Radarsat.)
The time available for glacier movement is half the orbital period (98.74 minutes) or 49.37 minutes for a single cycle. That pencils out to 3.57 m for Jakobshavn assuming peak velocity of 52 m/day, far less for Petermann.That's the orbital period in minutes but since the Earth is rotating under the orbit that translates to halving the 12-day repeat-period into six days.
Sort of wonder if Dark Snow and Black & Bloom (see below) need their own thread, a la Icebridge, but as Dark Snow posts are in here....
Black & Bloom is a UK project that's working alongside (and with what appears some overlap) Dark Snow, on Greenland. Lots of info. and updates, etc. here:
https://blackandbloom.org/
h/t Peter Sinclair (https://climatecrocks.com/2016/07/11/fish-out-of-water-whats-a-marine-biologist-doing-on-the-ice-sheet/)
Can't see anywhere better to ask this...
Greenland ice sheet is estimated to contribute about 7.2 metres to global sea level when it melts away.
That contribution is due to the melting of all the ice above sea level becoming water, as all below sea level dose not contribute to sea level rise if it melts, apart from a small fraction due to thermal expansion.
But has anybody estimated what the effect on sea level rise will be from the resulting isostatic rebound? Assuming it all rebounds to near or above present-day sea level, that displacement would add several metres more to the current maximum estimated sea level rise. Same goes (much more, I imagine) for Antarctica too as it also has a massive ice overburden on top of land held below sea level which will no doubt rise (and hence displace ocean) when the load is removed.
My guess is that the rebound deficit would be on the order of the density difference between the rock and the ice. Enough rock would go up to replace the push of the ice. The rock is much denser than ice and it takes a long time so...
But that rebound volume has to come from somewhere. The surrounding sea floor perhaps? So the overall effect would be none. Just a guess.
But has anybody estimated what the effect on sea level rise will be from the resulting isostatic rebound? Assuming it all rebounds to near or above present-day sea level, that displacement would add several metres more to the current maximum estimated sea level rise. Same goes (much more, I imagine) for Antarctica too as it also has a massive ice overburden on top of land held below sea level which will no doubt rise (and hence displace ocean) when the load is removed.
Globally, isostatic rebound does not affect sea levels.Glacial Isostatic Adjustment (GIA) - correction is used in altimetry when deriving global mean sea level:
Globally, isostatic rebound does not affect sea levels. Locally, sea levels may well fall along the Greenland coast, at least in the short run, both from isostatic rebound and from gravitational effects (the mass of the ice sheet pulls the surrounding ocean towards it).
Interesting - and makes sense. I stand corrected!Globally, isostatic rebound does not affect sea levels.Glacial Isostatic Adjustment (GIA) - correction is used in altimetry when deriving global mean sea level:
http://sealevel.colorado.edu/content/what-glacial-isostatic-adjustment-gia-and-why-do-you-correct-it (http://sealevel.colorado.edu/content/what-glacial-isostatic-adjustment-gia-and-why-do-you-correct-it)
I don't really understand when you talk about the flow of "rock" - isostatic rebound is caused by magma in the mantle shifting about. "Continental rock" presumably means continental crust, and "oceanic rock" ocean crust. Neither sees any volume change due to isostatic pressure changes. The density of the mantle is thought to be 3.3 in the top layers, probably slightly higher below the continental crust than under the oceanic crust.
Globally, isostatic rebound does not affect sea levels. Locally, sea levels may well fall along the Greenland coast, at least in the short run, both from isostatic rebound and from gravitational effects (the mass of the ice sheet pulls the surrounding ocean towards it).
Wow.. that raise a really interesting isostatic problem (Finally a post in my field).
Lets assume that the mass change in a column of the ocean with added water has to be isostatically balanced by a mass change in a column of continental rock (otherwise rock will flow from the high to low pressure as evidenced by post glacial rebound).
...
However, a second assumptions is that the volume of rock does not change globally. ... volume change of oceanic rock matches continental rock.
I don't really understand when you talk about the flow of "rock" - isostatic rebound is caused by magma in the mantle shifting about. "Continental rock" presumably means continental crust, and "oceanic rock" ocean crust. Neither sees any volume change due to isostatic pressure changes. The density of the mantle is thought to be 3.3 in the top layers, probably slightly higher below the continental crust than under the oceanic crust.
You are right of course - the mantle is rock, not magma. And the mantle does flow - and has a density of 3.3 in the top layers. Your previous use of the word "rock" seemed to indicate the crust given the density values you gave. The crust does not "flow", i.e. there is no shifting of material from oceanic to continental crust.
I don't really understand when you talk about the flow of "rock" - isostatic rebound is caused by magma in the mantle shifting about. "Continental rock" presumably means continental crust, and "oceanic rock" ocean crust. Neither sees any volume change due to isostatic pressure changes. The density of the mantle is thought to be 3.3 in the top layers, probably slightly higher below the continental crust than under the oceanic crust.
Rock does flow: Mantle convection is not from movement of magma, you only get melt where the solidus of the rock approaches the geotherm, such as mid ocean ridges, underneath hotspots, in thinning events or where fluids are injected, such as subduction zones. There is unlikely to be any partial melt underneath Greenland. Much of Greenland is (we believe) ancient shield rock.
I'm using conservation of volume of rock to calculate how much the extra water in the oceans would push down of the ocean floors and thereby increase the height of the continents. Of course, that takes 1,000s or 10,000s of years to happen.
One further interesting point is that the water on the Greenland ice sheet is close to the axis of rotation of the earth. Distributing that mass over the oceans will cause the earths rotation to slow by a tiny amount.
Ice-penetrating radar and ice core drilling have shown that large parts of the north-central Greenland ice sheet are melting from below. It has been argued that basal ice melt is due to the anomalously high geothermal flux that has also influenced the development of the longest ice stream in Greenland.
Here we estimate the geothermal flux beneath the Greenland ice sheet and identify a 1,200-km-long and 400-km-wide geothermal anomaly beneath the thick ice cover. We suggest that this anomaly explains the observed melting of the ice sheet's base, which drives the vigorous subglacial hydrology and controls the position of the head of the enigmatic 750-km-long northeastern Greenland ice stream.
Our combined analysis of independent seismic, gravity and tectonic data implies that the geothermal anomaly, which crosses Greenland from west to east, was formed by Greenland's passage over the Iceland mantle plume between roughly 80 and 35 million years ago.
Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures
Biological activity is a major factor in Earth’s chemical cycles, including facilitating CO2 sequestration and providing climate feedbacks. Thus a key question in Earth’s evolution is when did life arise and impact hydrosphere–atmosphere–lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800–3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals1, 2 from the Isua supracrustal belt (ISB), southwest Greenland3. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1–4-cm-high stromatolites—macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia4, 5. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration by 3,700 million years ago (Ma), near the start of Earth’s sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life’s origin in the Hadean eon (>4,000 Ma)6.
<snip>We based our project on more than 37,000 optical images collected by multiple sensors aboard the U.S. Geological Survey (USGS) and NASA’s Landsat satellites. The data span the period between 1972, when Landsat 1 was launched, and 2015, using data from Landsat 8 (launched in 2013), although most of the Landsat scenes were acquired after 1998.More at the link: https://eos.org/project-updates/using-landsat-to-take-the-long-view-on-greenlands-glaciers
We will continue to extend the database using new scenes recorded by the ongoing Landsat 7 and 8 missions. The USGS Landsat Global Archive Consolidation (LGAC) will add even more scenes, providing access to Landsat data that are archived at individual international ground stations [Wulder et al., 2016]. For Greenland, this could provide a considerable number of scenes from Landsat 4 and 5, dating back to 1982.
These additional images are valuable for extending the time span of the velocity time series. This greater time span is particularly important for inferring flow velocity variations that occur within the span of one season, and it may help to close observation gaps that occurred before 1999, when Landsat 7 was launched. Moreover, in regions of extensive cloud coverage, collecting Landsat scenes over a longer time span increases the chance of obtaining cloud-free data.
Enhanced Data Processing Provides a Clearer Picture
For 302 glaciers all around Greenland, we have processed more than 100,000 flow velocity fields from 1972 to 2012. We have extended this processing to include velocity fields for about 50 major glaciers up to 2015 so far.
By adding a quality flag that indicates the reliability of the data, we reduced the number of existing velocity fields with extensive outliers. We used an outlier detection strategy that compared the differences between each observed velocity product and a theoretically derived velocity field to compile the statistical parameters for our evaluation. Altogether, we have made more than 40,000 flow velocity fields accessible so far, and we continue to add new velocity fields as we process more data.
Rosenau et al. [2015] described a number of steps included in the processing procedure. We have improved the correction for tilt and terrain effects (orthorectification) using the Global Digital Elevation Map Version 2 (GDEM V2) from NASA’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The improved orthorectification step, in particular, facilitates the usage of overlapping scenes from orbits that are not repeat passes. The ability to include these additional scenes provides a much higher effective sampling rate than would be provided by repeat-pass sampling, which is limited to the repeat orbit of 16 days (Landsat 4 to 8 ) or 18 days (Landsat 1 to 3).
In 2003, a small pair of mirrors (the scan line corrector) aboard Landsat 7 failed, introducing data gaps as well as small shifts between the scan lines. We applied a destriping correction to mitigate the impact on the resulting velocity fields. In addition, we removed outliers using an adaptive, recursive filter approach. The combination of all these improvements leads to higher accuracy of the inferred velocity fields.
Long-Term and Seasonal Trends in Flow Velocity
The long time span covered by the Landsat scenes allows us to determine long-term flow velocity trends. The high temporal resolution lets us analyze seasonal flow velocity variations of numerous outlet glaciers. However, the pattern of temporal and spatial distributions of the flow velocity changes is not uniform (Figure 1). The monitoring system provides a powerful tool to examine the flow velocity pattern throughout time and space, and we have detected an acceleration pattern for a number of outlet glaciers.
I just found this in today's Washington Post, am not entirely sure where the best place to put it is, and am not sure I know how to link so feel free to move it if I link properly but in a poor area and let me know if the link is bad.The link worked for me with a slight modification http://wapo.st/2lyasOz (http://wapo.st/2lyasOz)
A project started by NASA five years ago is starting to pay off. It is called OMG for "Oceans are Melting Greenland" and it is basically trying to see what temperature differentials are doing to underwater glacier masses at various levels. So far ... does not look very good but not enough data has been observed and I doubt that the current administration will allow much more to be collected.
Will try to leave a link here >>http://wapo.st/2lyasOz?tid=ss_mail (http://wapo.st/2lyasOz?tid=ss_mail)<<
...
“It’s too early” to run the model, said Mathieu Morlighem, a researcher at the University of California and the lead author of one of the papers presenting the accumulating data. “I think you need to wait another year or two, maybe more. It was not possible at all before OMG.”
Still, the recently published findings mark a start. Morlighem’s study, for instance, looked at the depth and shape of the seafloor near the fronts of and beneath numerous Greenland glaciers. The research shows that numerous glaciers extend deeper beneath the surface of the ocean than previously thought.
For instance, Store Glacier in northwestern Greenland (at around 70 degrees North latitude in the image above) starts at 400 meters (around 1,300 feet) deep where its front touches the ocean, and then plunges to depths as high as 1,000 meters deep (3,280 feet) farther inland — making it quite vulnerable to the ocean. Prior research, however, had suggested the glacier was much shallower.
The same was true of numerous other glaciers, which also appear more vulnerable than previously thought.
“OMG is transforming our knowledge of which glaciers are vulnerable to more warming or not,” Morlighem said. “So I wouldn’t say we have been surprised; it’s more, we had no idea, for many of these fjords, what they were looking like.”
Overall, the data are also showing that Greenland’s west coast is far more vulnerable, in general, than its east, Morlighem said.
The second study, meanwhile, examines ocean circulation around the Greenland coast and finds, strikingly, that between 68 degrees North latitude along the coast and 77 degrees North (see above), the deepest warm layer of Atlantic water cools from 3.5 degrees Celsius down to 2.5 degrees Celsius. Moreover, it does so in part because the water busily melts away at a large and deep glacier called Upernavik at 73 degrees North, which touches the ocean in 675 meter (over 2,000 foot) deep waters. The cold meltwater from the glacier spills into the ocean and, through mixing, cools the warm Atlantic water somewhat.
“The glaciers there are actively losing enough ice, and enough fresh water, that it’s important for the oceanography, and how the water changes as it goes up the west coast of Greenland,” says Willis. That in itself is proof that Greenland is melting quite a lot.
The big picture is that NASA’s new data suggest — that’s right — new vulnerabilities.
“Overall, together I think these papers suggest that the glaciers as a whole are more vulnerable than we thought they were,” Willis said. He says that, of course, with the aforementioned caveat that NASA is not ready yet to feed the data into a model that actually shows how this could play out over the decades of our future.
...
identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt−1, or ∼14% of the Greenland total.”
NSIDC's greenland-today is back online for 2017. No action yet.
http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)
NSIDC's greenland-today is back online for 2017. No action yet.
http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)
There has been a tiny bit of action. Look very carefully on Cumulative Melt Days Jan 1 - Apr 11 at bottom SW corner and there are 2 light blue pixels !!!
NASA OMG blog by science communicator Laura Faye Tenebaum on Greenland: "A vast melting desert."
".....Over my headset, I can hear the pilots discussing the flight path with the instrument engineers. Out the window, I can see Greenland’s northernmost glaciers below us; white upon white upon white. They sure appear stable, still, enduring. But they’re not. They’re melting..."
https://climate.nasa.gov/blog/2578/a-vast-melting-desert/
Good read.
Good article Cate. Thanks for the link.
I don't get the warm spell forecast for northerly Greenland around May 4-5. The weak low moving in from Baffin doesn't seem to carry much atmospheric moisture, and it's a little early for the sun to have much warming power that far north. Is it some unusual cloud condition causing increased downwelling ILR?
If the forecast verifies, attendant surface melt will be quite early for that location.
.... and it's a little early for the sun to have much warming power that far north. Is it some unusual cloud condition causing increased downwelling ILR?
If the forecast verifies, attendant surface melt will be quite early for that location.
Thanks Magnamentis. excuse my ignorance. In view of rising temperatures in the Arctic, there must be increasing numbers of moulins contributing to the destabilisation of the Greenland ice sheet? Another positive feedback factor? Or am I off track?I would say the main factor is not the moulins themselves but the amount of surface melt and total meltwater. More meltwater will probably lead to more moulins. Surface melt in turn depends on the weather in Greenland which isn't necessarily in lockstep with the whole arctic.
Thanks oren :) I was thinking that water drainage through moulins might cause heating of the ice sheet from below leading to destabilisation, in comparison to water that drained straight into the sea.You are indeed right AFAIK.
Thanks oren :) I was thinking that water drainage through moulins might cause heating of the ice sheet from below leading to destabilisation, in comparison to water that drained straight into the sea.Something to think about, though I've never noticed it being considered, is that much of inland Greenland is well below sea level, I can't imagine any scenario where the salt from the ancient seas that covered it didn't end up in the lowest troughs, once these deposits begin to dissolve the melting temp. of that basal ice will be @ -5C. With more melt above we get more melt below.
A possibly interesting question:Thanks oren :) I was thinking that water drainage through moulins might cause heating of the ice sheet from below leading to destabilisation, in comparison to water that drained straight into the sea.Something to think about, though I've never noticed it being considered, is that much of inland Greenland is well below sea level, I can't imagine any scenario where the salt from the ancient seas that covered it didn't end up in the lowest troughs, once these deposits begin to dissolve the melting temp. of that basal ice will be @ -5C. With more melt above we get more melt below.
observations of the land surface now below the ice suggest that there were river valleys before ice covered the land. If the weight of the ice pushed the land surface below the sea level there would not be salt below the ice.
One of the biggest problems is of course that we cannot see through ice perfectly to assess the geology and its chemistry. When ice sheet mass balance changes, this can open old faults and close other ones in bedrocks (these tremors are called ice quakes). A far bigger problem could be if a new fault forms into rock salt containing minerals thus releasing and dissolving salt away, the saline brine might then get flushed out into the subglacial base together with warm water. Has there any hot springs in Greenland to support such a possibility (salt under ice)?[/quote]
.....
The olivine group minerals (especially peridotite) within deeper rocks in the crust and on the surface of the mantle may get partially dissolved triggering a re-start of volcanism in the highly volcano-infested South East Greenland (which has so far sat quietly under thickening snow cap even until now despite all the melting already). But as ice thins, the nucleation of gasses in volcanic reservoirs turn them foamy and more voluminous - thus sending magma to the upward trajectory to form magma incursions beneath ice sheet. Further down mantle - and over the wider areas - the conversion of wet solidus into dry solidus can intensify the overall negative pressure of volcanic plume solids (due to disassociation of hydrogen and oxygen from the rock making it lighter like cork or sea ice that float on water and rise upwards towards the surface).
One of the biggest problems is of course that we cannot see through ice perfectly to assess the geology and its chemistry. When ice sheet mass balance changes, this can open old faults and close other ones in bedrocks (these tremors are called ice quakes). A far bigger problem could be if a new fault forms into rock salt containing minerals thus releasing and dissolving salt away, the saline brine might then get flushed out into the subglacial base together with warm water. Has there any hot springs in Greenland to support such a possibility (salt under ice)?
.....
The olivine group minerals (especially peridotite) within deeper rocks in the crust and on the surface of the mantle may get partially dissolved triggering a re-start of volcanism in the highly volcano-infested South East Greenland (which has so far sat quietly under thickening snow cap even until now despite all the melting already). But as ice thins, the nucleation of gasses in volcanic reservoirs turn them foamy and more voluminous - thus sending magma to the upward trajectory to form magma incursions beneath ice sheet. Further down mantle - and over the wider areas - the conversion of wet solidus into dry solidus can intensify the overall negative pressure of volcanic plume solids (due to disassociation of hydrogen and oxygen from the rock making it lighter like cork or sea ice that float on water and rise upwards towards the surface).
Greenland melting quite high 18th & 19th May- especially on SW coast.
Does Greenland Melting Season deserve a thread of its own?
Greenland melting quite high 18th & 19th May- especially on SW coast.
Does Greenland Melting Season deserve a thread of its own?
Cor! Thanks. I hope there are chances of images where melting is biting hard.Greenland melting quite high 18th & 19th May- especially on SW coast.
Does Greenland Melting Season deserve a thread of its own?
Good idea. We've had one every year so far, I believe. Here it is: Greenland 2017 melt season (http://forum.arctic-sea-ice.net/index.php/topic,2054.0.html)
My PhD is in geochemistry so I know some pretty weird things. For a nice short write up about volcanic rocks in Greenland check out this NASA blog post.
https://blogs.nasa.gov/icebridge/2013/04/16/post_1366140794166/
The Skaergaard intrusion is a layered igneous intrusion in the Kangerlussuaq area, East Greenland. It comprises various rock types including gabbro, ferro diorite, anorthosite and granophyre.
Discovered by Lawrence Wager[1] in 1931 during the British Arctic Air Route Expedition led by Gino Watkins, the intrusion has been important to the development of key concepts in igneous petrology, including magma differentiation and fractional crystallisation[2][3] and the development of layering.[4][5] The Skaergaard intrusion formed when tholeiitic magma was emplaced about 55 million years ago,[6] during the initial opening of the North Atlantic Ocean. The body represents essentially a single pulse of magma, which crystallized from the bottom upward and the top downward. The intrusion is characterized by exceptionally well-developed cumulate layering defined by variations in the abundance of crystallizing olivine, pyroxene, plagioclase and magnetite.
The Skaergaard is perhaps the simplest and smallest of a group of gabbroic complexes of similar age that occur along the central coast of East Greenland, which together with coeval flood basalts are part of the North Atlantic large igneous province.
And now Greenland is burning, though it has happened before.
More pics here: https://twitter.com/Pierre_Markuse/status/894461039609352192
Two new studies of Greenland, using sophisticated technologies and large scientific teams to pull together and process the data, have now gone further in taking the full measure of the island through that ever-so-basic scientific act: mapping.
The first, a comprehensive seabed mapping project, relying in part on new data from NASA’s OMG (“Oceans Melting Greenland”) mission, concludes that the Greenland ice sheet is far more exposed to the planet’s warming oceans than previously known — and has more ice to give up than, until now, has been recognized.
Meanwhile, on Wednesday, a separate team of scientists used another quite different large-scale mapping exercise to document a surprising — but closely related — change in Greenland’s above-water topography. Publishing in the journal Nature, they showed that the contours of the huge island are changing because with all the ice melt rushing from glaciers to the sea, river deltas are expanding outward — a rare occurrence these days when deltas around the world are generally retreating, threatened by rising seas (think of the Mississippi River delta, for instance, and its vanishing wetlands).
Global sea level rise will be one of the major environmental challenges of the 21st Century. Oceans Melting Greenland (OMG) will pave the way for improved estimates of sea level rise by addressing the question: To what extent are the oceans melting Greenland’s ice from below?
This simulation of Greenland is the result of work carried out by the ISSM team for the SeaRISE experiments (Bindschadler et al., 2013, Nowicki et al. I, 2013, Nowicki et al. II, 2013) in which modeling teams from around the world compared their simulations against one another. One goal among others was to understand the impact of lubrication/friction at the ice/bedrock interface, and how the ice would speed-up if the friction coefficient α was reduced by a factor of two. Here, you will be able to replicate this experiment and play with a global reduction of Greenland friction coefficient up to 5% of its 2010 value.
https://vesl.jpl.nasa.gov/research/ice-sheets/giscui/ (https://vesl.jpl.nasa.gov/research/ice-sheets/giscui/)
Researchers at the University of California at Irvine (UCI), NASA and 30 other institutions have published the most comprehensive, accurate and high-resolution relief maps ever made of Greenland's bedrock and coastal seafloor. Among the many data sources incorporated into the new maps are data from NASA's Ocean Melting Greenland (OMG) campaign.From today's linked article:
Produced by researchers at British Antarctic Survey (BAS), University of Bristol and University of California at Irvine (UCI), the printed map is unveiled this week at the American Geophysical Union meeting in New Orleans.
"Greenland Basal Topography BedMachine v3" is the new 1:3,500,000 scale map created from data collected by over 30 institutions.
Read more at: https://phys.org/news/2017-12-reveals-landscape-beneath-greenland-ice.html#jCp
I wonder what is the relationship between the "new Greenland map" Adam Ash reported on above (November 7) and this one ["published this week (Thursday 14 December 2017)"].
From November 7 linked article:QuoteResearchers at the University of California at Irvine (UCI), NASA and 30 other institutions have published the most comprehensive, accurate and high-resolution relief maps ever made of Greenland's bedrock and coastal seafloor. Among the many data sources incorporated into the new maps are data from NASA's Ocean Melting Greenland (OMG) campaign.From today's linked article:QuoteProduced by researchers at British Antarctic Survey (BAS), University of Bristol and University of California at Irvine (UCI), the printed map is unveiled this week at the American Geophysical Union meeting in New Orleans.
"Greenland Basal Topography BedMachine v3" is the new 1:3,500,000 scale map created from data collected by over 30 institutions.
Read more at: https://phys.org/news/2017-12-reveals-landscape-beneath-greenland-ice.html#jCp
"I don't think so."
If this is in reference to Wilson, which bit don't you agree with ? I thought the mass balance study from DEM was plausible, but i am willing to be convinced otherwise.
sidd
I think i agree with you that 79N does not provide much backpressure, but i also think that Wilson et al. are correct in the 79N will continue to thin.
sidd
A treasure trove of information about Greenland and the Arctic is now at the disposal of the world’s researchers, thanks to a project under the auspices of Aarhus University.
The database is part of the Greenland Ecosystem Monitoring (GEM) project and the data has been collected by researchers who have returned again and again to the same places to measure the same things in the same way, reports Videnskab.dk.
A treasure trove of information about Greenland and the Arctic is now at the disposal of the world’s researchers, thanks to a project under the auspices of Aarhus University.
The database is part of the Greenland Ecosystem Monitoring (GEM) project and the data has been collected by researchers who have returned again and again to the same places to measure the same things in the same way, reports Videnskab.dk.
That Hill paper is brilliant. Check out figs 7,8,9. Open access.
sidd
WASHINGTON — A company that fleet operator Iridium formed to help finance its second-generation satellite constellation is taking longer than expected to pay Iridium back for carrying its sensor network to orbit.
McLean, Virginia-based Iridium said Feb. 22 that to avoid counting on aircraft-tracking startup Aireon for liquidity, Iridium went back to its lenders to raise additional debt to finish the $3 billion Iridium Next constellation it’s in the midst of deploying.
Next SpaceX launch in late March
Iridium CEO Matt Desch said the successful Feb. 22 launch of a SpaceX Falcon 9 from Vandenberg Air Force Base cleared the way for greater schedule certainty with Iridium Next, which is launching entirely from the California facility. So far SpaceX has completed four Falcon 9 launches for Iridium, and has four more to go, though the original launch campaign was supposed to have been completed in 2017.
The fifth Iridium Next launch will likely occur March 29, he said. Subsequent missions should follow every five to six weeks until the constellation is complete, he said. Each launch carries 10 satellites at a time, with the exception of the sixth launch, which will carry five Iridium Next satellites and two U.S.-German science satellites called GRACE-FO.
The GRACE-FO, or Gravity Recovery and Climate Experiment Follow-On satellites, were originally supposed to launch on a Dnepr rocket through the Russian-Ukrainian joint venture Kosmotras, but the mission never happened. Iridium had two satellites slated to launch on Dnepr as well, but booked a shared Falcon 9 after Russian red tape left the launch, once forecast for 2015, on indefinite hold.
GRACE-FO will launch as part of a commercial rideshare mission with five Iridium Communications Inc. satellites aboard a SpaceX Falcon 9 rocket. The Iridium-6/GRACE-FO launch is scheduled for no earlier than 1:03 p.m. PDT (4:03 p.m. EDT) May 19 from Vandenberg Air Force Base in California.
Tracy and Heilprin were first observed by explorers in 1892 and have been measured sporadically ever since. Even though the adjoining glaciers experience the same weather and ocean conditions, Heilprin has retreated upstream less than 2.5 miles (4 kilometers) in 125 years, while Tracy has retreated more than 9.5 miles (15 kilometers). That means Tracy is losing ice almost four times faster than its next-door neighbor.
Using ocean data from NASA's Oceans Melting Greenland (OMG) campaign, the study documents a plume of warm water flowing up Tracy's underwater face, and a much colder plume in front of Heilprin.
A huge iceberg has drifted close to a village in western Greenland, prompting a partial evacuation in case it splits and the resulting wave swamps homes. The iceberg is looming over houses on a promontory in the Innaarsuit village but is grounded and did not move overnight, local media say.
Local officials say they have never seen such a big iceberg before.
Last summer, four people died after waves swamped houses in northwestern Greenland after an earthquake. Those of Inaarsuit's 169 residents living nearest the iceberg have been moved, Danish news agency Ritzau said. "There are cracks and holes that make us fear it can calve anytime," village council member Susanne Eliassen told the local newspaper Sermitsiaq. The village's power station and fuel tanks are close to the shore, she said. Some experts have warned that extreme iceberg events risk becoming more frequent because of climate change. This in turn increases the risk from tsunamis.
A nice reminder that when Greenland's glaciers calve, big stuff falls off.Here's how such "big stuff" falls off.
A nice reminder that when Greenland's glaciers calve, big stuff falls off.Here's how such "big stuff" falls off.
https://www.youtube.com/watch?v=hC3VTgIPoGU
More recent "big stuff" falls off:
https://www.theverge.com/2018/7/9/17550966/greenland-helheim-glacier-calving-icebergs-video
More "big stuff" becoming "big stuff".A nice reminder that when Greenland's glaciers calve, big stuff falls off.Here's how such "big stuff" falls off.
https://www.youtube.com/watch?v=hC3VTgIPoGU
More recent "big stuff" falls off:
https://www.theverge.com/2018/7/9/17550966/greenland-helheim-glacier-calving-icebergs-video
...
Subglacial bed topography is probably the most important input parameter in an ice sheet model and remains challenging to measure. The bed controls the flow of ice and its discharge into the ocean through a set of narrow valleys occupied by outlet glaciers. I am hoping that the new product that I developed, called BedMachine, will help reduce the uncertainty in numerical models, and help explain current trends.
...
Sermip Nunataa (Nunatak-Island within ice sheet glacier) was a nunatak of the southern Greenland Ice Sheet between Sermilik Brae and Sondre Qipisaqqu Brae. Here we examine changes from 1993-2018 of the margin of the ice sheet in the area and the impact on this and neighboring nunataks.
In 1993 the Sermip Nunatak was 2.5 km inland from the ice sheet margin. ...
Published on Jul 16, 2012or, per Google Translate
7 juillet 2007
Rushes du film « Home » :Survol du glacier de Sermilik Brae au Groënlandcertains icebergs retournés de couleur bleutée. Images d'archive INA
Institut National de l'Audiovisuel
Published on Jul 16, 2012[map from the 'From a Glacier's Perspective' article]
July 7, 2007
Rushes from the film "Home": a flyby of the Sermilik Brae Glacier at Greenland some icebergs returned in bluish colour. INA Archive Images
National Institute of Audiovisual
(https://i.kinja-img.com/gawker-media/image/upload/s--ufWnL0AG--/ayqlhhuxllhn310ro0at.jpg)https://m.youtube.com/watch?v=vTr3VdGlFr8
https://gizmodo.com/a-massive-impact-crater-has-been-detected-beneath-green-1830437095/amp
Hidden beneath Hiawatha Glacier is a 31-kilometer-wide impact crater, big enough to swallow Washington, D.C., Kjær and 21 co-authors report today in a paper in Science Advances. The crater was left when an iron asteroid 1.5 kilometers across slammed into Earth, possibly within the past 100,000 years
The timing is still up for debate, but some researchers on the discovery team believe the asteroid struck at a crucial moment: roughly 13,000 years ago, just as the world was thawing from the last ice age. That would mean it crashed into Earth when mammoths and other megafauna were in decline and people were spreading across North America.
The impact would have been a spectacle for anyone within 500 kilometers. A white fireball four times larger and three times brighter than the sun would have streaked across the sky. If the object struck an ice sheet, it would have tunneled through to the bedrock, vaporizing water and stone alike in a flash. The resulting explosion packed the energy of 700 1-megaton nuclear bombs, and even an observer hundreds of kilometers away would have experienced a buffeting shock wave, a monstrous thunder-clap, and hurricane-force winds. Later, rock debris might have rained down on North America and Europe, and the released steam, a greenhouse gas, could have locally warmed Greenland, melting even more ice.
(https://i.kinja-img.com/gawker-media/image/upload/s--yxt5ih42--/di2kikauteoqymsrtgrx.jpg)
Preliminary evidence suggests it happened relatively recently. The crater appears to be well-preserved—a surprising observation given that ice is a powerful erosive force. The crater is likely fairly young from a geological perspective.
Open Access: Kurt H. Kjær et.al., A large impact crater beneath Hiawatha Glacier in northwest Greenland (http://advances.sciencemag.org/content/4/11/eaar8173), Science Advances 14 Nov 2018
Have you seen the Greenland map Espen once posted, with hundreds of named glaciers?Nope - perhaps I will search for it. Too many glaciers!
Actually I just recalled it's in the sticky thread in this very sub-forum. "Google Maps with place names Greenland." It was started by Espen, but the map was posted by A-Team a bit down the thread.Found it. Almost impossible to read the names, but the really interesting thing is showing the velocity of movement that also shows up the catchment area of each glacier and where they merge into the main ice sheet..
Found it. Almost impossible to read the namesclick on the map.... then select VIEW on the bar at the top of the screen.... pump the ZOOM UP. Makes the print a bit more readable.
Very nice paper by Trusel et al. on the acceleration in GIS melt beginning at the start of the Industrial Revolution. I see that Fettweiss is an author.There is a caveat. It is no surprise that summer melt is going up. But the melt happens in the brief Greenland Summer - June July & August. Surface Mass increases during the other 9 months - snow. The average net addition to mass in a year (Snow less melt - SMB) is about 400 GT. But calving exceeds this by about 200GT per annum
"Our results show a pronounced 250% to 575% increase in melt intensity over the last 20 years, relative to a pre-industrial baseline period (eighteenth century) ..."
"rates of meltwater production, refreezing and runoff across much of Greenland are all at multi-century highs ...
"The onset of industrial-era Arctic warming occurred in the mid-nineteenth century [21] and differential smoothing analysis likewise indicates increases in GrIS runoff initiated shortly thereafter (Fig. 4b; Methods). The median onset of positive trends in GrIS runoff are also coincident with the median onset of weakening Atlantic meridional overturning circulation [9] . Emergence of runoff beyond the natural range of variability, however, has only very recently occurred ..."
"Today, surface melting and melt-induced runoff in Greenland occur at magnitudes not previously experienced over at least the last several centuries, if not millennia."
sidd
The net change in (2018 mass of the ice sheet overall, including this higher discharge of ice directly into the ocean, is not clear at this point but may be a smaller loss or even a small gain. This is similar to our assessment for 2017, and in sharp contrast to the conditions for the preceding decade.
"Large ice loss variability at Nioghalvfjerdsfjorden Glacier, Northeast-Greenland"
(Christoph Mayer et al.) July 2018
https://www.nature.com/articles/s41467-018-05180-x.pdf
BBR, SO2 from Russia hardly "plunged" from 1981-88, more like 10% reduction in the figures. Helpful but unlikely to stop acid rain?A much larger % was captured during this time as well. SO2, besides causing acid rain, reduces incoming solar insolation and temperatures. Maybe the global reduction was to blame? I know the US was also cleaning up during the 80s but would assume "clean-up" was more effective in USSR due to its economic meltdown (i.e., less SO2 emitting activity in general).
Lurk,
Why don't you check your sources. The original Nature paper says a geothermal heat flux of 93 mW per sq. m., whilst the popular version talks about 100 MW per sq. m. I know it may not seem important to you, but to some, m&M may make a difference.
Are you being paid for sowing confusing seeds in the various Neven seedbeds?I am not known to agree with Lurk much but I protest the slanderous insinuation.
In his post he makes assumptions about variations in geothermal heatflux may be a contributing factor in the 79N glacier demise.
However, the reason for the large interannual fluctuations of
the thinning rates revealed by this study still need to be found
(...)
Thus, while our
analysis suggests that the ocean is likely the main driver of the
observed changes at 79 North Glacier, the regional dynamics that
control the heat transport into the ice shelf cavity and other
contributors, such as subglacial discharge induced by surface melt
or geothermal heat flux will need further attention to fully
understand the observed thickness evolution.
Hence, this part of Greenland may play a role for the rapid basal melt located at the head of the Northeastern Greenland ice stream and its high ice speeds. In addition, the newly discovered 52 hydrothermal vent complexes13, some of which reach up to 11 km in diameter, in the Danmarkshavn Basin and in the Thetis Basin is located just outside the ice-stream outlet glaciers; Nioghalvfjersbræ, Zachariæ Isstrøm and Storstrømmen (Fig. 5). These complexes are formed from hot intrusions (c. 1200 °C) at 1–2 km depth in the Thetis Basin and >3 km depth in the Danmarkshavn Basin. Hence, this accumulated evidence point to active geothermal activity in the northeastern corner of Greenland and indicate that geothermal heat source may exist below the center and northeastern part of GIS. This heat source may explain the origin of the Northeast Greenland ice stream and other areas with high ice stream speed.
And then in his reply to me has the nerve to blame the editor of Science Daily for not catching an error made in the Press release from Aarhus University.
Abstract
Recent acceleration of Greenland's ocean‐terminating glaciers has substantially amplified the ice sheet's contribution to global sea level. Increased oceanic melting of these tidewater glaciers is widely cited as the likely trigger, and is thought to be highest within vigorous plumes driven by freshwater drainage from beneath glaciers. Yet melting of the larger part of calving fronts outside of plumes remains largely unstudied. Here we combine ocean observations collected within 100 m of a tidewater glacier with a numerical model to show that unlike previously assumed, plumes drive an energetic fjord‐wide circulation which enhances melting along the entire calving front. Compared to estimates of melting within plumes alone, this fjord‐wide circulation effectively doubles the glacier‐wide melt rate, and through shaping the calving front has a potential dynamic impact on calving. Our results suggest that melting driven by fjord‐scale circulation should be considered in process‐based projections of Greenland's sea level contribution.
Plain Language Summary
As the world warms, loss of ice from the Greenland Ice Sheet will be a significant source of sea level rise. Greenland loses ice partly through the flow of huge rivers of ice called tidewater glaciers that dump solid ice directly into the ocean. Over the past two decades, tidewater glaciers around Greenland have accelerated dramatically, increasing Greenland's contribution to global mean sea level. There is mounting evidence that these accelerations have been driven by ocean warming, and a resulting increase in the rate at which the ocean melts the front of tidewater glaciers (called submarine melting). Yet submarine melting is at present poorly understood, in part due to the danger and difficulty of collecting data close to tidewater glaciers. We present observations of the ocean in front of a tidewater glacier that are unprecedented in their proximity to the glacier. These data reveal an ocean circulation which flushes warm water along the front of the glacier, driving high rates of submarine melting. We then use a numerical model to identify what drives this circulation. Our results are an important step toward understanding a key process which will modulate future sea level contribution from the Greenland ice sheet.
Lurk was using this number ...
By all means, carry on posting "news" like you have done in this particular thread, but please read the articles you intend to "flag" before you hit the keyboard. Self control is also about keeping the "noise level" down to the benefit of both yourselves and the remaining followers of this fine forum.I am sure we are all immensely grateful for your advice.
Earth’s oldest soil could be tucked away in an ancient rock outcrop in Greenland, according to new research. Dating back some 3.7 billion years, the suspected soil—exposed underneath a retreating ice cap—could potentially contain fossilized traces of primordial life.
The new study, published this week in the awkwardly named science journal Palaeogeography, Palaeoclimatology, Palaeoecology, opens thusly: “Soil formation is a combination of physical, chemical, or biological processes important for regulating planetary atmospheres, and the ultimate source of essential nutrients such as phosphorus for the nutrition and origin of life.”
Indeed, soil—unlike sterile bits of rock or sand—serves as a natural medium for the growth of land plants. Identifying our planet’s oldest soils, therefore, is of critical importance to scientists who study Earth’s formative period and the emergence of our planet’s first organisms.
The new study, led by University of Oregon geologist Greg Retallack and Old Dominion University geologist Nora Noffke, describes a tantalizing new rock outcrop in the Isua Greenstone Belt of southwestern Greenland that, quite possibly, contains our planet’s oldest dirt, and by consequence, the oldest traces of life on the planet.
It’s not actually dirt—it’s a substance known as paleosol, former soil that’s been packed tightly into solid rock.
Remnants of Earth's Oldest Dirt May Have Been Found in Greenland[/b]Would this paleosol have any analog to sandstones?
Earth’s oldest soil could be tucked away in an ancient rock outcrop in Greenland.....It’s not actually dirt—it’s a substance known as paleosol, former soil that’s been packed tightly into solid rock.
Total Ice Mass Balance
GRACE satellite data can be used to estimate monthly changes in the total mass of the Greenland ice sheet, as done in the past (e.g., Tedesco et al., 2017). However, the NASA GRACE mission, which started in 2002, ended in October 2017. Hence, there are no data available on the total mass balance for the 2017/18 season. The GRACE Follow On (GRACE-FO, https://gracefo.jpl.nasa.gov/) mission was launched on 22 May 2018. Data acquired since its launch are currently under review for quality control. The May 2018 launch means that no data are available from space between October 2017 and May 2018. Processing of the GRACE-FO dataset will provide estimates of total mass change anomalies for the summer of 2018 and will be calibrated to data acquired by GRACE.
Even in the age of the Sagas and the Vikings there existed an ice-bearing current on the east and northeast coasts of Greenland. But the current in those days cannot be compared to the present one, neither in extent nor in its importance to navigation. This fact I attribute to a more vivid circulation in the Irminger Sea in former days. According to the researchers of the Danish Ingolf expedition, the bulk of the Gulfstream branch known as the Irminger current turns westward at the entrance to the Denmark Strait and runs along the east coast of Greenland forming the underlayer of the ice-bearing polar current. According to Hambergs investigation in 1883 this warm underlayer melts the ice of the polar current and the amount of drift-ice on the eastcoast of Cape Dan in lat. 65 1/2º will vary with the strength of the Irminger current. South of Cape Farewell the ice turns west and northwest collecting outside the sosuthwestern coast of Greenland (Juliane-haabs Distrikt). Here 8-9 centuries ago the Icelandic colonists found an open sea. Now it is blocked by ice all summer because the Irminger current is too weak to melt de ice before it reaches Cape Farewell.
A small increase in the temperature of the under layer, or a stronger influx of Gulf stream water, or a stronger oscillation in the border-stratum causing a more vivid contact of the waters of the two currents would scatter the drift-ice so that the neighbourhood of Cape Farewell would be free from ice and the deep sounds between that island and the main land open to navigation. Later we shall see the importance of these sounds for the journeys of the Viking-settlers.
The formation of the coast in the lat. of Cape Dan causes the drift-ice to scatter after the passage of the Denmark Sound. The scattering of the ice and the action of the Irminger current which still in its full force crosses over from Iceland to Greenland makes the neighbourhood of Angmangsalik (Cape Dan) more accessible from the east than the southernmost point of Greenland<./p> Nordenskiöld was the first in modern time to profit by this when in 1883 he broke through the thin ice-layer outside Cape Dan and anchored his ship "the Sophia" in King's Oscar's harbour. (lat. 65º 35'). The stronger development of the Irminger current a thousand years ago brought two important consequences:
1. The climate of Österbygden (the eastern settlement) was more temperate because the sea coast was free from ice, whereas the district of Julianehaab has an ice-bound sea in front and the inland-ice behind.
2. As the ice did not go round Cape Farewell and enter Davis Strait, Baffin Bay and the Labrador-current were also relatively free from ice. This again influenced the climate of New Foundland and North America. It is also probable that the warm under current which runs through Davis Strait, like the Irminger current and the rest of the western Gulf stream-branches, was otherwise developed in those days. In other words: that the polar ice then melted at higher latitude than now.
At the end of the Middle-ages a change came in these conditions, which can only be explained by an alteration in the oceanic circulation. Such changes in the oceanic circulation will of course be more perceptible in the border-areas where the waning Gulf stream branch contents with currents of the northern origins as in Cattegat, the Baltic, Baffin Bay and at the south-point of Greenland. It is inconceivable that a state of equilibrium lasting through thousands of years should exist in those parts. Even now the conditions, especially the ice conditions, vary greatly from year to year in these seas. In Greenland there are good ice-years and bad ones. Now I will show the conditions in south Greenland in a good year like 1883 when Nordenskiöld on the Sophia landed at Fredriksdal and penetrated into the sounds north of Cape Farewell which had not been navigated by European ships since the days of the Vikings. Then I will give an instance of the conditions and the route of navigation in a bad year like 1902 as described by the Danish archeologist Captain Bruun.
Finally I will draw a comparison between these conditions and those which prevailed a thousand years ago when Iceland and Greenland were colonized and the Norsemen discovered America. In our time the east coast of Greenland from 65º lat. to Cape Farewell is almost inaccessible.
In good years the pack-ice may form a narrow belt along the coast. But the pressure of this ice-girdle, which is packed close to the coast whenever the wind blows in that direction, is almost more formidable to navigators than in bad years when the ice spreads for miles over the sea but generally leaves an open channel along the shore. This channel was used by the Danish expeditions under Graah, Holm and Garde o.a. Nansen too used this channel to get to the point from whence he started on his ice-wandering after he had landed on the drift-ice and carried his boats across it, just as they did in cases of emergency in ancient times, as is told in Kungaspegeln (the King Mirror) from the 13th century. Doubtless 600-700 years ago it was at times dangerous and even impossible to penetrate to the east coast of Greenland if it happened to be a bad ice-year.
But it must be remembered that in the Viking-age such years were exceptions and not the rule as is now the case. In spite of the strong tidal currents the sounds between Cape Farewell and the mainland are now always blocked by drift-ice which is crammed into their eastern inlets by the polar current outside. West of Cape Farewell there is the great fjord-district with the settlements of the ancient "Eystribyggd". All summer the Bay is blocked by drift-ice, and navigation is generally impossible till authum and then only by circuitous routes as shown by the dotted lines in the map of plate 11.
Circumstances being exceptionally favourable, Nordenskiöld was able to get to Julianehaab as early as the 17th June 1883. It is generally necessary to wait till late in summer and, working through the ice-girdle, make the coast by the northliest route through Nunarsiut Sound then go south-wards on an inner route along the coast of Julianehaab and Fredriksdal which is the farthest accessible settlement. From here the expeditions of Wallö, Giesecke, Graah, Holm and Garde in Eskimo boats penetrated through the sounds north of Cape Farewell: the Ikerasak, the Ikek, the Tunua, the Kipisak a. o. which, though never sounded, were found to be navigable up to their eastern inlets, where the ice of the polar current was encountered. In spite of the favourable conditions in 1883 Nordenskiöld had no better luck. He was turned back by the ice when trying to penetrate through the sounds and was unable to reach the east coast. Such are the conditions in a good ice-year. The ice-charts of 1903 and Captain Bruun's description of his journey to Greenland in the summer 1903 show how the navigation must be performed in a bad year.
Very nice gerontocrat.The following article describes how the little ice age that was supposed to have driven away the Viking settlers from Greenland is a myth.
Do you know how conditions today compare to those in the past?
The Greenland Ice Sheet emits tons of methane according to a new study, showing that subglacial biological activity impacts the atmosphere far more than previously thought.
... Professor Jemma Wadham, Director of Bristol's Cabot Institute for the Environment, who led the investigation, said: "A key finding is that much of the methane produced beneath the ice likely escapes the Greenland Ice Sheet in large, fast flowing rivers before it can be oxidized to CO2, a typical fate for methane gas which normally reduces its greenhouse warming potency."
... With Antarctica holding the largest ice mass on the planet, researchers say their findings make a case for turning the spotlight to the south. Mr Lamarche-Gagnon added: "Several orders of magnitude more methane has been hypothesized to be capped beneath the Antarctic Ice Sheet than beneath Arctic ice-masses. Like we did in Greenland, it's time to put more robust numbers on the theory."
Guillaume Lamarche-Gagnon et al. Greenland melt drives continuous export of methane from the ice-sheet bed (https://www.nature.com/articles/s41586-018-0800-0), Nature (2018).