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Author Topic: What's new in Greenland?  (Read 98224 times)

crandles

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Re: What's new in Greenland?
« Reply #250 on: May 22, 2017, 01:18:08 PM »
Greenland melting quite high 18th & 19th May- especially on SW coast.

Does Greenland Melting Season deserve a thread of its own?

I suggest multiyear images from
http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/

such as attached

Neven

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Re: What's new in Greenland?
« Reply #251 on: May 22, 2017, 01:51:19 PM »
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
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gerontocrat

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Re: What's new in Greenland?
« Reply #252 on: May 22, 2017, 02:00:27 PM »
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
Cor! Thanks. I hope there are chances of images where melting is biting hard.
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VeliAlbertKallio

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Re: What's new in Greenland?
« Reply #253 on: May 25, 2017, 04:19:04 AM »
I was referring to this landscape on the Geikie Peninsula which is definitely volcanic as you can see (and NASA article put it quite nicely). What still bothers me is that these volcanoes go there beneath the ice sheet almost forever (!) and then you cannot see every volcano on the surface - much like the Gamburtseve Range they are hidden deep in Antarctic ice.

It bothers me how uniform the volcanic rocks there are and what faults in the rocks might be therein. Just like Toba and Yellowstone aren't really very active volcanic systems today to fear, there is some tiny bit of beast still left in them (this justifying some fear of future supereruptions).

My concern or fear is that if huge ablation of ice takes place stresses by ice-forced subsidence reverberates to the old faults or creates new ones and incursion of hot water or rocks would come active under ice just like Nanortalik hot springs. The partial melting of Peridotite isn't easy to come, I admit, but the weight of ice sheet influences bedrocks and has a very deep footprint which I think is generally underestimated:

I see here a clear connection between central Greenland subglacial depression, volcanic incursions on the east coast of Greenland and proximity of the vast volcanic shield of Iceland nearby all in connection. Whilst I am aware of the drifting of a volcanic hotspot and believe it to be the strongest today in Iceland, I do not see an absolute reason why not residual activity pockets could not exist in Greenland. True, in Hawaii the volcanic activity diminishes towards North East.

There are extinct volcanoes in Antarctica, but also some others that aren't and keep wondering if any system is left in limbo in Greenland that could start playing up due to wet solidus damage strengthening regional plumes in mantle due to ablation and then nucleation of gases within magma reservoirs (if there were any near surface).

After all, I also note that if these volcanoes really are so old (those NASA guys did not walk on the mountains but flew over in altitude, sic), in many of them appears far too little erosion if they were millions of years old as you follow NASA argument - but sharp volcanic forms appear not always planed smooth by ice. Long periods of ice and glaciation tends to smoothen the rocks round but I can't see often rocks smoothened by ice in this volcanic region, do you have any explanation to that? This isn't Grand Canyon region carved by river, but area which ought to be carved by ice. Look at the rocks elsewhere Greenland and see how rounded ice has made them.

So, I am still afraid that they could cause Jokullhaups and contribute as ice sheet mass balance is impacted. For example, looking at the Gamburtsev Range volcanoes profiles in ice, it has been claimed that the ice sheet on that region was "growing from bottom up" by ice upwell (ice sheet growing from its base upwards).

I have interpreted these Gamburtsev features the other way round: the volcanoes have dumped latent heat during the ice sheet by melting ice and so destroying the ice sheet stratification there as the compacted snow melted and then turned next into frozen water ice (rather than compacted snow what it was before the heat incursion event I suspect occurring there). I support heat possibility because we have seen Vatnajokull producing Jokullhaups with huge bursts of water by volcano melting, but if the water could not escape out and once the effusive eruption fizzles out the water will freeze just the way the Gamburtsev Range soundings look like.

I would not take NASA airborne people's expedition at face value, I would rather see them going on foot and kicking stones around to come to conclusions like mine that the ice has not sufficiently shaped the mountains to justify them a greatly different age and origins to those in Iceland. I did not say that I have seen live volcanoes, but can feel suspicious of lack of planing effect of ice.

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/

FredBear

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Re: What's new in Greenland?
« Reply #254 on: May 25, 2017, 12:12:44 PM »
VeliAlbertKallio, the landscape looks similar to Spitsbergen (pointed mountains) and the "layer-cake" of rocks have obviously been eroded for some considerable time. In my opinion the layers are not distorted as they might  be in more active zones (but this is just a snap-shot)?

lifeblack

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Re: What's new in Greenland?
« Reply #255 on: May 25, 2017, 07:35:59 PM »
VelliAlbertKallio, while the peaks in the picture have an overall shape that suggests they are younger than suggested elsewhere, the features that are visible are clearly all erosional, and none of the pyramidal shapes in view were erupted as cone shaped mountains  (ie, none of the features are from a partially eroded cascade-type stratovolcano).  As evidence, look at the stacked layers of lava that are visible - they were clearly emplaced as (apparently) continuous sheets on a nearly level landscape, and they remain nearly horizontal today.
As for the height of the mountains after so many millions of years of glaciation, I might be going out on a limb here, but I think that as the rock gets eroded away, the crust will rebound upwards in response to the removal of the top layers.

I would definitely be interested in whether there are any moribund volcanic sources in Greenland that may be reactivated by decompression melting, but the landscape in  the picture doesn't seem to be good evidence of anything recent

Tor Bejnar

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Re: What's new in Greenland?
« Reply #256 on: May 25, 2017, 08:34:08 PM »
The following information is from a geologic map of Greenland, with my leading comments:
It appears the youngest igneous rocks in Greenland are on the order of 50 million years old.  I wouldn't expect the removal of all Greenlandic ice to re-energize significant (or actually any) volcanic activity. From here: "Extinct: It takes a lot to be an “extinct” volcano. The rule of thumb I use is about 1 million years since the last eruption … "


Chart describing last 100 million years of igneous rocks in Greenland (see time line screen shots):
(references are to time line reference numbers)

 
[6] Paleocene tholeiitic lavas, central West Greenland.
[7] Paleocene picritic lavas, central West Greenland.
[48] Eocene tholeiitic plateau basalts in East Greenland.
[49] Paleocene–Eocene tholeiitic basalts with picritic intervals. East Greenland.
[53] Tertiary felsic intrusions in East Greenland.
[57] Tertiary mafic to intermediate intrusive complexes in East Greenland.
[58] Upper Cretaceous gabbroic intrusion. Pearya terrane, Ellesmere Island (Canada).
« Last Edit: May 25, 2017, 08:46:52 PM by Tor Bejnar »
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VeliAlbertKallio

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Re: What's new in Greenland?
« Reply #257 on: May 26, 2017, 04:48:40 AM »
Very many thanks for the highly constructive points raised! Please note that  I raise these here as highly speculative stipulations and as a sort of brainstorming attempt and I do not see - at least for now any evidence - of geological activity. Yet, I wish to raise further detailed points for your consideration.)

I'm enclosing a very typical scenery of glacier-shaped rocks and boulders from Greenland. Even volcanic rocks, as hard they may be, are impacted and subjected to the milling of ice domes from above (if rocks were covered by one). I have seen many volatile structures on that region (unlike the Svalbard) that do not appear in any way round but look like a frozen in time, a still frame. The overall appearance is similar to water-flooding impacted strata of the Grand Canyon region, not an ice sheet gourged one. For me, the region has perhaps undergone strong isostatic uplift, but it was impacted by water floods, Jokullhaups, turning it to the Grand Canyon of Greenland. It is not geomorphic according to the ice sheet planing, if it were the volcanic mountains would have a distinctive smooth rise facing the direction ice sheet had flowed, with steep rear sides.

Source of these floods would then be Jokullhaups.

The volatile structures preserved is, therefore, suggestive to me that the rocks were hot when the ice sheet was forming (and hence expelling the local ice development unlike elsewhere). As Jokullhaups periodically discharged water and lahar, the loose, slushy stratum eroded rapidly.

If so, then the volcanic incursion is associated with the Central Greenland's subsidence when the ice dome was being deposited onto the Precambrian granites across Greenland. Thus, the incursion of magma is a result of ice sheet compressing subglacial magma reservoir and driving a partial melting of asthenosphere beneath the glaciating region - with the partial melting breakdown products being driven out here near this edge area of Greenland continental plate (where plate's weaknesses are greatest). The only option is for me to go and collect more volatile rock structure evidence which would dispel the idea of ice having carved out this peculiar area. That's a future project for me and these expeditions are costly!

There are earthquakes and the Nantortalik hot spring. I suspect that there must be more hot springs hidden beneath ice sheet as the faults are myriad. Hot springs could be behind some of the subglacial heat anomalies are found in various parts of Greenland. Today more pressurized water is fed into subglacial faults by water from moulins that are becoming increasingly active over perimetrical subglacial bedrock. Moulins one day number in millions over perimeter shield.

I expect the volcanic region (potentially) evolving to the Mascarene volcanism. A two-phase volcanism where a low viscosity, vast lava floods are followed by a long non-active interval to the previous episodes of vast effusive volcanic eruptions. Then a smaller secondary episode re-emerges a new bout of different type of volcanism which shatters the old crust and causes mountain incursions to pierce the old, lava field by the extremely high viscosity (cool) secondary lavas. This renewal of eruptivity thus shatters the solidified ('extinct') flat lava volcano field. The secondary volcanism in the Mascarene volcanos had so high viscosity that many eruptions caused vertically rising lava floods (like a toothpaste comes out of the tube when it is pointed upwards).

In the Mascareane volcanism, the force of high viscous rock oozing through flat lava field was so great that nearly all secondary volcanoes go vertigo through the plain, lava rising vertically skyward. Even parts of the old solidified lava crust sitting as a tip of the newly oozing highly viscous lava with the old solid blocks of lava becoming a mushroom-like 'hat' shapes for the volcano, i.e. Peter Both 'hat' cap. https://upload.wikimedia.org/wikipedia/commons/b/b3/Pieter_Both%2C_mountain.jpg These vertical formations rising from flat lava landscapes.

The question is of course how solid is the high viscous incursion and whether such incursions could make way up once Greenland ice sheet melts. What drives high viscous lava up is not exactly clear but some disassociation of gases must have happened, maybe further afield, pressure change reverberated from nucleating lavas elsewhere to make cool rocks to cause secondary Mascarene eruptivity. In the case of deglaciation, this could be the secondary trigger, whereas the low viscous eruptivity would have been the primary trigger, a forming ice sheet.

It is my view that the secondary Mascarene volcanism was driven by gaseous disassociating within low viscous magmas in long distance, perhaps when the hot spot was already transiting from Mauritius to nearby Reunion. Events in Iceland and/or deep partial melting in asthenosphere under Greenland could be the source to force old cool lavas in Greenland once the ice sheet mass balance losses become large enough to create Mauritian style new volcanic life on the old volcanic region.

By the way, whilst climbing to study Mount Lepus I came also across old continental blocks of rock embedded in these high viscous plumes of semi-solid rocks that had broken through the primary plain of solidified lavas and seabed. (Only years after people theorized this sunken continent.)


« Last Edit: May 26, 2017, 04:59:15 AM by VeliAlbertKallio »

Hyperion

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Re: What's new in Greenland?
« Reply #258 on: May 26, 2017, 12:22:47 PM »


Certainly some spectacular igneous pancaking in the Geike Area.



This seems to be the Skaergaard intrusion some 55 million years ago. Possibly ASSOCIATED with the PETM.
Wikipedia:
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.

I say associated because looking at the some 50ma glaciated alternating with some 100ma hothouse approximate periodicity of the last about 500ma. These Large Igneouse events seem very much clustered in the transition of meltdown. Quite plausibly causation is the deglaciation. rather than the result. Or more precisely a cyclic melt loading and unloading process causing the repeated addition of sills. Both under the ice sheets during mass loss cycles. And at distances where the super heated fluid basalt emerges through deep dyke conduits from the glaciated continent keels as hot spots or super-swells. Or from rift zones to allow spreading  when the rebuilding of icecaps as ice mass starts to destabilize and oscillate.

Heres a list from wikipedia. And a picture of the Longest seamount chain in the world left by the hotspot thats thought to have caused the biggest eruption we know of. The Ontong-Java event. The Louisville hotspot probably connects with central West Antarctica. And whats left of WAs bum is the Hikurangi,  Manihiki, Ontong Java Plateaus, and Sth Pacific Superswells. Whether Greenlands bum is going to keep feeding Iceland, or Nth Canada and Iceland feed Greenlands bum in the near future, who can say.



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RoxTheGeologist

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Re: What's new in Greenland?
« Reply #259 on: May 26, 2017, 04:43:59 PM »

I think Palaeomagnetic evidence places East Greenland at around 60N when the hotspot was causing volcanism.  Is there any evidence of glaciation from that period in Greenland, or the extent of ice sheets if any? I think that the earth was pretty hot at that time, there was a long term warming event that covered the period when Greenland moved over the hotspot, so there was unlikely to be an ice sheet at all.

The North American plate is moving north west relative to the hot spot frame of reference, away from the Icelandic hotspot. Greenland has been moving in the same direction pretty much since the opening of the North Atlantic. The magma chambers that were created in Greenland by the hotspot are cold and eroded, as evidenced from the pictures. Ice unloading will not reawaken any volcanism associated with that hotspot in Greenland. It might increase the activity in Iceland.

RoxTheGeologist

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Re: What's new in Greenland?
« Reply #260 on: May 26, 2017, 04:49:32 PM »

This is worth reading, and shows how the lithosphere below Greenland is now high density, and therefore cold:

https://www.researchgate.net/figure/33681824_fig7_Figure-5-Present-day-tomographic-image-c-of-the-Iceland-hotspot-plume-modified-from

sidd

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Re: What's new in Greenland?
« Reply #261 on: May 26, 2017, 07:56:51 PM »
Fascinating soliton in ice stream going down Rink. May be associated with hi-melt summers. Requires only one bedrock GPS station time series (and some orbiting satellites ...).  The authors clearly share some of Saruman's [1] traits. Wonder if such events can be teased out by ground GPS around Jacobshawn.

Very pretty paper. Read all about it:

https://www.jpl.nasa.gov/news/news.php?feature=6857

open access  doi:10.1002/2017GL073478

I attach Fig 3c), 3d) and S11

The captions for 3c) and d) are

"(c) Pattern of mass deficit transiting the Rink Glacier during 2012 summer. About − 7.1 m of monthly thinning over the optimal domain (blue fill within the glacier trunk outlined by white line) is required to explain the mean monthly displacement (red arrow). Plotted are also the magnitudes and fulcrum positions of monthly mass anomalies (circles) that satisfy the measured monthly displacements (arrows). Notice the down glacier propagation of (negative) mass anomaly that represents the negative phase of mass transport wave. Mean monthly SMB loads are shown in the background. (d) Same as Figure 3c but for the fall/midwinter season that follows. It requires about 2.8 m of monthly thickening over the optimal domain (red fill within the glacier trunk) to explain the mean monthly displacement (blue arrow)."

The caption for S11 is in the image

sidd

[1] "His knowledge was deep, his thought was subtle, and his hands marvellously skilled ... " Tolkien, Lord of the Rings, v III, Ch. X, 1954


Reallybigbunny

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Re: What's new in Greenland?
« Reply #262 on: May 27, 2017, 12:40:21 PM »

johnm33

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Re: What's new in Greenland?
« Reply #263 on: May 27, 2017, 12:53:44 PM »

Hyperion

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Re: What's new in Greenland?
« Reply #264 on: May 31, 2017, 04:20:45 PM »
Dang! This "new mode of glacial acceleration" seems like the slushalanche effect I've been predicting from the spreading and thickening sub surface slushifer discovered in 2011. If this starts to be the new normal behaviour of glacial outflows in Greenland and WA we are looking at big trouble. If a big late summer weather system rains heavily over Greenland. say from a stuck planetary wave in the jets, and a big low in the fram vicinity lifting surfacing gulfstream heat and moisture, with a Greenland/ CAA high. its not difficult to imagine a whole lot going at once. Perhaps 40 days and nights of rain COULD cause abrubt slr.  :o
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Jester Fish

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Re: What's new in Greenland?
« Reply #265 on: June 06, 2017, 01:09:40 AM »
Above normal temps forecast for June, July, August for Greenland.  I haven't checked out the forecasting verification.
 
http://iri.columbia.edu/our-expertise/climate/forecasts/seasonal-climate-forecasts/

solartim27

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Re: What's new in Greenland?
« Reply #266 on: August 07, 2017, 08:11:21 PM »
Wildfires?  (Cross post from Wildfire thread)
And now Greenland is burning, though it has happened before.
More pics here:  https://twitter.com/Pierre_Markuse/status/894461039609352192
FNORD

Tor Bejnar

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Re: What's new in Greenland?
« Reply #267 on: August 07, 2017, 08:31:05 PM »
Greenland burning:  see also posts in Greenland 2017 melt... thread starting here.
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nukefix

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Re: What's new in Greenland?
« Reply #268 on: August 11, 2017, 11:41:04 AM »
A beautiful Sentinel-1 track crossed Greenland yesterday...while sightseeing I managed to spot both the Greenland summit site and the NEGIS coring site on the imagery. Images downloaded from PolarView.

Tor Bejnar

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Re: What's new in Greenland?
« Reply #269 on: August 11, 2017, 07:22:21 PM »
The biggest fire continues to spread.  Image from Sentinel Playground August 8.  I'm showing the color bands choices. (8/8/17 image is latest.) Note scale in lower left corner.  (click if you like)
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be cause

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Re: What's new in Greenland?
« Reply #270 on: August 11, 2017, 07:57:00 PM »
be the cause of only good
and love all beings as you should
and the 'God' of all Creation
will .. through you .. transform all nations :)

solartim27

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Re: What's new in Greenland?
« Reply #271 on: August 16, 2017, 05:44:32 AM »
FNORD

nukefix

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Re: What's new in Greenland?
« Reply #272 on: August 16, 2017, 11:23:50 AM »
Amazing blue iceberg spotted in Jakobshaven icefjord:

http://apps.sentinel-hub.com/sentinel-playground/?lat=69.16542768047643&lng=-49.78935241699219&zoom=12&preset=1_NATURAL_COL0R&layers=B02,B08,B12&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-08-10&cloudCorrection=none&atmFilter=ATMCOR&showDates=true&evalscript=

sidd

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Re: What's new in Greenland?
« Reply #273 on: August 18, 2017, 12:09:21 AM »
A paper by Kulessa et al is pessimistic on future sedimentary control on glacier veelocity as melt season lengthens and enroaches deeper into the ice sheet. Some modelling using CISM, bed hydro is finally being cracked. Open access. read all about it.


DOI: 10.1126/sciadv.1603071

http://advances.sciencemag.org/content/3/8/e1603071

sidd

Juan C. García

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Re: What's new in Greenland?
« Reply #274 on: October 05, 2017, 08:55:32 PM »
Washington Post: Scientists mapping Greenland have produced some surprising – and worrying – results

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).
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

A-Team

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Re: What's new in Greenland?
« Reply #275 on: October 13, 2017, 01:59:44 PM »
The first article mentioned in the post above, Morlighem 2017, represents a very substantial refinement in mapping of Greenland fjords whose bathymetry is key to warm ocean water access to the grounding lines of the glaciers.

The article is open access and even better, so is the data. That's a first. It's all packaged as a single giant 2.5 GB netCDF file and stored at NSIDC at the link below (nuisance registration req'd). The download opens readily as seven Panoply map options despite the immense grid of 18346 x 10218 = 187,459,428 cells.

BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multi-beam echo sounding combined with mass conservation
M. Morlighem et al 2017  open source 8.5 MB
http://onlinelibrary.wiley.com/doi/10.1002/2017GL074954/full
http://sites.uci.edu/morlighem/dataproducts/bedmachine-greenland/
http://nsidc.org/data/IDBMG4# netCDF file 2.5 GB
https://icdc.cen.uni-hamburg.de/1/daten/land/geoid-eigen.html EIGEN-6C4
https://www.nytimes.com/2017/09/12/magazine/what-could-we-lose-if-a-nasa-mission-goes-dark.html GRACE replacement

This frees us from external dependencies on map generation for favorite forum areas such as Petermann, Jakobshavn and Zachariae. We can likely improve on journal illustrations using the seven mappable GEO2D files. The authors' motivation for netCDF is to enable Greenland-wide forecasting models such as ISSM which is far too computationally intensive for us.

A post on another forum complains about ESRL using a spherical earth approximation instead of the ellipsoid WGS84 approximation (these differ by 1 part in 300) but the authors here are dismissive of WGS84  and use an earth geoid, a 2014 product called EIGEN-6C4, a high-resolution global gravitational field model. It's a correction on EGM2008. WGS84 is off by as much as 64 m error in Greenland which defeats the whole purpose of OMG fjord bathymetry.

The European Improved Gravity model of the Earth by New techniques includes data from the Gravity field and Ocean Circulation Explorer (GOCE) satellite. While its role is fundamental in geodesy, the importance for Greenland arises from improved orbital description of the failing GRACE satellite which is critical to mass balance measurements.
« Last Edit: October 13, 2017, 03:14:31 PM by A-Team »

Tealight

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Re: What's new in Greenland?
« Reply #276 on: October 14, 2017, 11:25:46 PM »
The new BedMachine v3 is really great for marine terminating glaciers. Finally the bedrock map is not cropped anymore in the important terminus region.

For Petermann and Zachariae not much has changed since version 2, but Jakobshavn looks quite different. I wonder if a slower flow speed influenced the mass conversion calculations.

The bedrock beneath the wedged part of Spaltegletscher is modeled as above sea level, which obviously can't be right. One of the weak spots of the mass conversion model.

click on images to animate

oren

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Re: What's new in Greenland?
« Reply #277 on: October 15, 2017, 12:04:49 AM »
@Tealight, thank you. Very interesting.

sidd

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Re: What's new in Greenland?
« Reply #278 on: October 15, 2017, 09:41:30 PM »
Sejr et al. on a 13 year hydrographic record from NE greenland, not quite as far north as the Flade Isblink papers i posted earlier on that thread.

DOI:10.1038/s41598-017-10610-9

Open access. Read all about it.

sidd

A-Team

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Re: What's new in Greenland?
« Reply #279 on: October 17, 2017, 03:11:29 PM »
Nice, T-lite! If you have that gif in a linear grayscale palette, it would be easy to make 3D surfaces of the trough. The newer over older below shows that depths at the calving front and preceding trough are now substantially shallower than in version 2.

Also adding below the best overall geoid I could locate for Greenland and the Arctic Ocean. Seems like there should be an interactive version or global geolocated netCDF and indeed finally located the former.

http://www.gfz-potsdam.de/en/section/global-geomonitoring-and-gravity-field/topics/terrestrial-and-airborne-gravimetry/icgem/

http://icgem.gfz-potsdam.de/vis3d/series visualization service
« Last Edit: October 17, 2017, 04:14:56 PM by A-Team »

AbruptSLR

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Re: What's new in Greenland?
« Reply #280 on: November 02, 2017, 10:31:55 PM »
The linked open access reference presents Bed Topography and Ocean Bathymetry that is useful in highlighting Greenland marine glaciers that are at risk of accelerated ice mass loss due to continued global warming:

M. Morlighem et. al. (1 November 2017), "BedMachine v3: Complete Bed Topography and Ocean Bathymetry Mapping of Greenland From Multibeam Echo Sounding Combined With Mass Conservation", Geophysical Research Letters, DOI: 10.1002/2017GL074954

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074954/full

Abstract: "Greenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine-terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach. A new 150 m horizontal resolution bed topography/bathymetric map of Greenland is constructed with seamless transitions at the ice/ocean interface, yielding major improvements over previous data sets, particularly in the marine-terminating sectors of northwest and southeast Greenland. Our map reveals that the total sea level potential of the Greenland ice sheet is 7.42 ± 0.05 m, which is 7 cm greater than previous estimates. Furthermore, it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which AW can access glaciers with marine-based basins, thereby highlighting sectors of Greenland that are most vulnerable to future oceanic forcing."
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Juan C. García

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Re: What's new in Greenland?
« Reply #281 on: November 03, 2017, 10:48:31 AM »
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?

https://omg.jpl.nasa.gov/portal/
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

johnm33

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Re: What's new in Greenland?
« Reply #282 on: November 03, 2017, 01:55:34 PM »
The thought crossed my mind that the changes in Jacobshavn may be due to the dissolving of ice welded rock/permafrost, or even a salt deposit being dissolved.

Adam Ash

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Re: What's new in Greenland?
« Reply #283 on: November 08, 2017, 02:06:37 AM »
https://www.nasa.gov/feature/jpl/new-greenland-maps-show-more-glaciers-at-risk

'New maps of Greenland’s coastal seafloor and bedrock beneath its massive ice sheet show that two to four times as many coastal glaciers are at risk of accelerated melting as previously thought.'

Sigh.

AbruptSLR

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Re: What's new in Greenland?
« Reply #284 on: November 10, 2017, 05:43:26 PM »
The linked open access reference provides updated information about the dynamics of dark ice in south-west Greenland:

Tedstone, A. J., Bamber, J. L., Cook, J. M., Williamson, C. J., Fettweis, X., Hodson, A. J., and Tranter, M.: Dark ice dynamics of the south-west Greenland Ice Sheet, The Cryosphere, 11, 2491-2506, https://doi.org/10.5194/tc-11-2491-2017, 2017.

https://www.the-cryosphere.net/11/2491/2017/

Abstract. Runoff from the Greenland Ice Sheet (GrIS) has increased in recent years due largely to changes in atmospheric circulation and atmospheric warming. Albedo reductions resulting from these changes have amplified surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of dark ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs) can be present on the surface, ranging from inorganic particulates to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large interannual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare ice sectors of the GrIS will evolve in the future, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades.

Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years but so too does its duration (from 0 to > 80 % of June–July–August, JJA), intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant interannual synoptic controls.

We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics. We suggest that whilst the spatial distribution of dark ice is best explained by outcropping of particulates from ablating ice, these particulates alone do not drive dark ice dynamics. Instead, they may enable the growth of pigmented ice algal assemblages which cause visible surface darkening, but only when the climatological prerequisites of liquid meltwater presence and sufficient photosynthetically active radiation fluxes are met. Further field studies are required to fully constrain the processes by which ice algae growth proceeds and the apparent dependency of algae growth on melt-out particulates.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Juan C. García

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Re: What's new in Greenland?
« Reply #285 on: December 05, 2017, 08:11:11 PM »
An interesting view of "before and after the inclusion of new OMG data" of Greenland bed floor, given on NASA page:

https://climate.nasa.gov/news/2646/new-greenland-maps-show-more-glaciers-at-risk/
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: What's new in Greenland?
« Reply #286 on: December 05, 2017, 08:34:05 PM »
Maybe you already know about these tools.
They are new for me...

Virtual Earth System Laboratory: https://vesl.jpl.nasa.gov/

Specially for Greenland:
Greenland Basal Friction.

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/
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.