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Martin Gisser

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Re: what's new in Greenland ?
« Reply #50 on: January 09, 2015, 03:10:28 PM »
2015 will be the year of foliations, principal curvatures and moving Darboux frames
Holla! 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.

A propos: How is the melt data doing? I'm actually just interested in a sum of 3-4 exponential functions (summing the different melt basins) to extrapolate the Greenland melt trend and the ensuing sea level rise -- just like wipneus's famous sea ice melt trend graphs. (The Frobenius theorem applied to foliated ice can wait.) Some years back my back-in-the head exponential estimamate was 1-2m SLR by 2100 from Greenland. Gavin was shocked ("that would be catastrophic"). Is there meanwhile enough data to justify a more elaborate graph, something to become wipneus' other world-famous graph, updated every year? It would be a "terrific" service for the lay audience.
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A-Team

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Re: what's new in Greenland ?
« Reply #51 on: January 09, 2015, 06:10:08 PM »
 
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.

I am planning to start a separate forum for 'Englacial Greenland or maybe 'Greenland in 3D + T' the very minute two key papers from AGU2014 become available. These would be the MacGregor database LAYERMAP of 21 years of radar stratigraphy and the Sommers PARCA flow lines from the summit. Lots of the forum will be coverage of published papers, no math for math's sake.

It seems to me we initially find ourselves not only in low dimensions but also strictly concerned with a specific embedding in R3xT so that much of the fancy geometry after Gauss/Riemann is either not applicable or collapses to something more familiar. There are some tensor bundles in the picture but no real topology; I'm not sure yet about a significant role for connections; for Lie groups, just SO(3), no finite groups really, but maybe dilational symmetry for time behavior of isochrons.

I am interested in efficient analytic expressions that keep track of these intersecting surfaces to replace pixel arrays. The main nuance here is catching layer deformation over bedrock. I don't anticipate too much along the lines of singularities or even complications like umbilical points.

Picking 3 foliations, say isotherm, isochron and isostress, they are going to intersect in a lattice. The main idea is a coordinate system may exist in which the Navier-Stokes equation is well-behaved (as an expression of conservation laws, aka symmetries, Noether). Developing the ice sheet on in lattice coordinates will then be vastly more computationally efficient. At any rate, saying goodbye to xyz numerical approximation theory and crunching of tesselation meshes.

This has to kept accessible to everyone who happens by. And that can only be done with pictures, we are not a math forum. However intuitive visualizations not only become more difficult to make with open source software, but also to share within the confines of the blog  (eg, no 3D interactive mousing).

So, one step at time, let's see how far it gets.

Meanwhile, take a look at this amusing piece at wikipedia -- it may come in handy for Greenland ice: https://en.wikipedia.org/wiki/Streamlines,_streaklines,_and_pathlines 

Did you ever see this thesis by Ed Boring on "Visualization of tensor fields". It gets pretty good toward the end.
http://www.ann.jussieu.fr/frey/papers/scientific%20visualisation/Boring%20E.,%20Visualization%20of%20tensor%20fields.pdf

Martin Gisser

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Re: what's new in Greenland ?
« Reply #52 on: January 09, 2015, 07:07:27 PM »
Hi A-Team, thanks! Will have a look at the Boring thesis Sunday night. I've studied stricly pure mathematic and as a hobby horse am currently putting Riemannian calculus on it's feet (physicist abstract index calculus with abstract indices replaced by uncompromising abstract multilinear algebra, plus doing the LeviCivita on cotangent space with a new fundamental lemma of Riemannian Geometry working with differentials...).

While I have a keen interest in physics I have always hated physicist math. The only thing I get is Einstein's field equation in vacuum :-). In geometry I even hate most of the mathematicians math, so I do my own tensor calculus now, so I can translate lots of superfluous mess to fit my low-IQ brain.

So, I am a total newbie to applied math and numerics (except that I've written the world's first raytracing graphics for toy computers of the 1980ies and attended a boring Fortran numerics class in the 1990ies). But maybe here's a point of entry. I hope this year to get a job as farm hand, to keep my brain power for myself to learn and work out some interesting stuff.

Another thing I want to extend this year is statistics (mostly for energy markets incl. grid balancing). Methinks for modelling of greenland ice dynamics this is as important as differential geometry. Alas I bet mostly Poissonian cracking and flushing. Apropos, my main subject of study in the 1990ies was stochastic diff. geom. i.e. Brownian motion. I have a purely abstract hunch (dream) this could help in numerics.
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Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #53 on: January 13, 2015, 08:41:33 AM »
New paper by Smith et a 2015 on Greenland drainage:
http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html

Martin Gisser

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Re: what's new in Greenland ?
« Reply #54 on: January 13, 2015, 04:33:39 PM »
New paper by Smith et a 2015 on Greenland drainage:
http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html

Video interview and some spectacular scenes from 2012 melt: http://www.latimes.com/science/sciencenow/la-sci-sn-catastrophic-greenland-melt-20150112-story.html

From paper abstract:
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
Why is the earth silent at this destruction? (Martin Heidegger ca. 1937)

A-Team

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Re: what's new in Greenland ?
« Reply #55 on: January 14, 2015, 12:55:57 AM »
Unexpected outcome from the new 0.5 m WorldView academic license:

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 motion
Did 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.

I'd say my top visualization priority is  of invariants of the deviatoric stress tensor. We need an intuitive exposition with simple pictures like the one the Brazilian prof wrote for the strain rate tensor. https://en.wikipedia.org/wiki/Strain_rate_tensor  See also https://en.wikipedia.org/wiki/Cauchy_stress_tensor
 
There is a very low level of pathology in the otherwise nice ice layering. The case below shows the oldest consistently traceable triple that we know from NEEM are ~85,000 years old. These are hugely important to the study of paleo-stability of the Greenland ice sheet.
« Last Edit: January 14, 2015, 12:51:08 PM by A-Team »

Martin Gisser

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Re: what's new in Greenland ?
« Reply #56 on: January 14, 2015, 02:50:46 AM »
Hi A-Team, thanks for the fascinating images!

What are these vertical white blurred stripes? Moulins? In the video interview on the paper mentioned above it was said the GIS is "Swiss cheese". Are there any radar images/sections where the cheese holes (moulins) are visible?

----------------
On Ricci flow: I haven't yet looked into the hard technical details. (The soft stuff, like evolution of curvature, is a paradigmatic example of mathematicians tensor calculus mess where you waste 90% of your IQ...) Why Ricci invented his tensor is a bit messy. He certainly wasn't thinking about Hamilton's Ricci flow or Einstein's field equation. Looks like Ricci wasn't even aware of the geometric meaning of the Ricci tensor: It is the quadratic approximation of the volume form - just like Riemann curvature is the quadratic approximation of the metric - in normal coordinates. Ricci flow looks like heat flow but is a very difficult nonlinear PDE that can blow up. (It took a crazy genius like Perelman to get the final knack.) Brownian motion may be of some use there, but extremely technical: diffusion on infinite dimensional (path) space.

------------------
Hmmm... so you are looking for some Riemannian metric for the ice sheet? And perhaps the best one could be approximated by Ricci flow? As I said me dunno anything almost of elasticity/fluid physics. But like to get there.

(Ha! My most reality based life dream is to find and marry a rich farmer girl and open a carbon negative dairy cow farm on Greenland. No kidding.)
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Neven

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Re: what's new in Greenland ?
« Reply #57 on: January 14, 2015, 07:56:40 AM »
Thanks for making me feel stupid, guys.  ;D
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icefest

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Re: what's new in Greenland ?
« Reply #58 on: January 14, 2015, 01:01:59 PM »
Thanks for making me feel stupid, guys.  ;D
I feel the same.
The more I learn the stupider I feel.
Open other end.

A-Team

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Re: what's new in Greenland ?
« Reply #59 on: January 14, 2015, 02:34:01 PM »
Neven/Icefest, don't worry, this will end up reading like a comic book. We are just thrashing around trying to figure which 0.00001% of modern geometry is applicable.

Martin, I have not see moulins in radar yet. The horizontal resolution of the main radar program is typically 1000 pixels for 50 km so a pixel column represents 50 m. The flight tracks are also fairly sparse. The moulins are mostly found south-centrally below the 2000 m contour, not the region with the most interesting radar stratigraphy. Snowmobile-drawn radar might have better resolution but they would not knowingly drive over a snow covered moulin.

So, to answer your question, personal drone radar can fly a tight 5 m grid but it has not yet been deployed in Greenland for this purpose (as far as we've been told). There must be quite a network of new and old moulins but there may not be enough contrast for them to stand out. If a barrel of sea salt had been added to the melt lake -- and the moulin water refroze in place -- that might provide enough dielectric.

Radar unfortunately does not go straight down like a focused laser beam; the return signal has reflected to various extents off everything in a fairly wide cone, so even if they chop to specified return times expected for a given reflector depth, other things can contribute, beyond what is directly below at that depth. So a 1-pixel vertical column is not fully separated from its adjacent pixels in some information-theoretic sense.

The worst-case scenario -- the white vertical flares that you see in the Petermann radar scan above -- arise from steep bedrock topography which the radar is striking obliquely; the slope is adding too much backscatter. The question is, since they are determining this topography on the fly, why don't they use it in buffered real time to dial back the flare where it is anticipatable?

They'll say it comes down to unfavorable signal to noise ratio. I'm not thrilled with that answer because it implies, wrongly, that the flare can't be reduced at all by after-the-fact digital imaging enhancement (photoshopping). Here adaptive (locally defined) contrast adjustment as in ImageJ2 can help with tracing stratigraphy layers continuously through the flares.

The imagery was never despeckled properly either. The whole 21 year Cresis archive needs to be reprocessed. I presume that was done in the course of developing the LAYERMAP dbase.

The backstory here: radar was initially tasked with just getting the bedrock topography and locating the oldest ice (flat deep thick isochrons along summit ridge). The electronics was optimized for that.

The goals have changed today (basal melt, isochronal surfaces, ice upheavals, englacial lakes) but the data archive has not. It is what it is; nobody is going to re-fly the grid.

The englacial radar is a seriously under-analyzed data set, maybe the worst case in the history of science. However people have caught on to the opportunities and the situation may be rectified in a year or so.

Below is a flare off a steep-walled ice upheaval (with some bedrock contribution). If these images were rescaled to 1:1, the horizontal would be ~25 x wider. They're very distorted as they stand.

This is most disturbing in the case of Greenland's so called Grand Canyon. How could they fill in the blanks between radar tracks? These are very sparse even in the most intensely surveyed regions -- even at a generous 100 m width, 98% of the tightest grid (Petermann) is completely devoid of observational data. Yet a whole lot of topography can and does happen over this 10 km gap scale. More on this shortly!
« Last Edit: January 14, 2015, 02:42:11 PM by A-Team »

Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #60 on: January 18, 2015, 12:39:56 PM »
From Applegate et al 2014:
"Our ice sheet model experiments represent crudely, or neglect, many processes that are important on the real ice sheet. In particular, both of the models we apply here use the positive degree-day method for calculating surface melt. Previous studies have shown that the positive degreeday method has shortcomings relative to more-sophisticated melt calculation schemes (e.g. Braithwaite 1995; van de Wal 1996; Bougamont et al. 2007; Robinson et al. 2010; van de Berg et al. 2011). We have not explored the effects of albedo feedbacks (Robinson et al. 2012), or changes in the distribution of temperature or precipitation over the year, on our model output. However, the ranges of the positive degree-day factors that we investigated in the SICOPOLIS ensemble are quite large (Applegate et al. 2012), suggesting that we have adequately explored possible variations in melt over the Greenland Ice Sheet’s surface.

Other processes that we parameterize or neglect include surface meltwater-driven lubrication of the ice-bed interface (this process is implicitly included in the profile model simulations; Zwally et al. 2002; Parizek and Alley 2004; Bartholomew et al. 2010; Shannon et al. 2013) and the penetration of warm ocean waters into fjords, accelerating the drawdown of ice through outlet glaciers (Joughin et al. 2008; Straneo et al. 2010). Including these processes in our simulations would likely shorten our estimated e-folding times, rather than lengthen them (e.g. Parizek and Alley 2004)."

Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #61 on: January 18, 2015, 02:50:29 PM »
Applegate et al also say:
"It might be argued that the plausible range of temperature changes is smaller than the one we report, because some models in the CMIP5 ensemble show less skill over Greenland than others (Belleflamme et al. 2013; Fettweis et al. 2013) and thus yield temperature changes that are too high or low. However, the CMIP5 ensemble provides only a limited sampling of uncertainties associated with model parameter values and initial conditions, which can be substantial (e.g. Stainforth et al. 2005; Deser et al. 2012; Olson et al. 2013). Thus, the range of plausible Greenland temperature changes that we derive from the CMIP5 ensemble might be too narrow, rather than too wide. Climate model calibration (e.g., Bhat et al. 2012) could help to reduce the range of plausible future temperature increases; such a calibration is beyond the scope of the present study."

Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #62 on: January 18, 2015, 03:00:57 PM »
And their last paragraph on policy implications:
"We speculate that near-term reductions in greenhouse gas emissions could pay large dividends in terms of avoided sea level rise. Our results suggest that the relationships between temperature change, GIS response time scale, and GIS equilibrium sea level contribution are approximately exponential (Fig. 2). Thus, the benefit, in terms of avoided sea level rise contributions from the GIS, of a unit of avoided emissions is greatest if emissions reductions are begun before much temperature change has already happened. Alternatively, one could say that mitigation becomes less effective in preventing or delaying sea level rise contributions from the Greenland Ice Sheet as temperature rises. Near-term reductions in greenhouse gas emissions may also buy time to design and implement improved strategies for adapting to sea level change."

Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #63 on: January 18, 2015, 06:49:50 PM »
From Todd & Christoffersen 2014 on Store Glacier, linked by A-Team earlier:
"Inland of Store’s stable frontal pinning point is a 28km long overdeepening reaching 950m below sea level (Fig. 2), which could make Store susceptible to sudden retreat, i.e. if the terminus becomes ungrounded from its current pinning point at 113km. We found that, by forcing the model with unphysically large values for submarine melt rate (not shown), we were able to force the terminus back off its pinning point, which led to rapid retreat through this trough. However, none of our climate forcing scenarios were able to trigger such a retreat, which suggests that the current configuration of Store is stable and will most likely remain so in the near future... Our model excludes the effect of water in surface crevasses, which may conceivably affect calving due to hydrofracture if water levels are high (Benn et al., 2007a). Although recent work included this effect (Nick et al., 2010), we ignore it because high-resolution images captured in repeat surveys of Store with an unmanned aerial vehicle in July 2013 detected water in only a small number of surface crevasses near the terminus (Ryan et al., 2014).Although we cannot exclude the possibility that undetected water is contributing to crevasse penetration, it is not necessary to invoke this process to explain the observed behaviour of Store."

So if in the future more melt water on the glacier would cause hydrofracture, calving may increase and maybe less (submarine) climate forcing is needed for the terminus to become ungrounded from its pinning point, possibly leading to rapid retreat.
« Last Edit: January 18, 2015, 10:49:15 PM by Lennart van der Linde »

Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #64 on: January 18, 2015, 10:57:00 PM »
I think this has been posted earlier in one of the Greenland threads, but for a good overview of the many marine based GIS-glaciers see (again) the supplement to Morlighem et al 2014:
http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf

They find more vulnerable (marine based) ice then estimated before.

A-Team

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Re: what's new in Greenland ?
« Reply #65 on: January 21, 2015, 07:00:12 PM »
Big news conference coming up tomorrow, Thursday 21 Jan 15. It involves the long-awaited paper by JA MacGregor sorting out 21 years the radiostratigraphic age structure of Greenland. There will be a press release from U Texas and simultaneous release of a sophisticated narrated animation by NASA Visualizations.

This is a huge breakthrough for Greenland glaciology and I'll be cross-posting about it for the rest of the month, mostly over at the Greenland subglacial topography forum.

The paper was released yesterday  in the 'reviewed, accepted" section of the Journal of Geophysical Research Earth Surface. The doi:10.1002/2014JF003215 is paywalled but the three animations are freely available from journal supplemental.
 
Alternatively, you can download an open source .zip file containing the 37 page article pdf, its 13 figures and 3 mp4 animations courtesy of the lead author. Getting the full 285.8 MB file to download caused me some esoteric unpacking grief in Chrome and Firefox but Safari worked right away. Below I've explained a few things in brackets and trimmed down the text:

283MB  ftp://ftp.ig.utexas.edu/outgoing/joemac/gris_strat_rev2.zip folder of pdfs

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].

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.


They are not calling it LAYERMAP any more -- that name is being reserved for a forthcoming project in Antarctica. The database of grids and traced reflections are headed to the NSIDC repository but they're not posted yet. However you can download them for now from the two ftp sites below. 

[I don't recommend these links. Better to wait a week for NSIDC to host urls and final data revisions].
1.5GB  ftp://ftp.ig.utexas.edu/outgoing/joemac/Greenland_radiostratigraphy.mat crashes Octave, should open QGIS
2.4GB  ftp://ftp.ig.utexas.edu/outgoing/joemac/Greenland_age_grid.nc opens in QGIS and Pandora

The raw layer data is in MATLAB HDF5 (for which you do not need $matlab). Due to gaps in layer tracing, this data may be split into multiple divisions which do not exactly correspond to CReSIS frame numbers. However you can go to the appropriate Cresis frame using the provided GPS time.

The layer data include the age that we assigned to the layer which from either from the 6 main drill cores or quasi-Nye strain law dating (Nye was a 1950's contemporary of Glen). For an example of the internal notation, gris_strat.campaign(17).segment(110).division(1) maps to Cresis 20110506_01 along the northwestern ice divide.

The age volumes and depths of specific isochrons -- obtained by IDW (inverse distance weighting) which they are calling kriging -- are in NetCDF. It's most convenient to view .nc files in Panoply freeware -- I gave the link a couple days back. The normalized age volume (age_norm) is the age of 25 thickness-normalized depths throughout the ice sheet. The isochron depths (depth_iso) include 11.7, 29, 57 and 115 kyr bands.

I've attached Fig3d -- a spectacular enhancement coming off NGRIP.
« Last Edit: January 23, 2015, 02:46:22 PM by A-Team »

AbruptSLR

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Re: what's new in Greenland ?
« Reply #66 on: January 21, 2015, 10:40:26 PM »
The linked reference (with an open access pdf) documents that two subglacial lakes suddenly drained (see attached image) beneath the GIS (that had previously been stable for at least decades), indicating that the GIS is sensitivity to climate change:

Howat, I.M., C. Porter, M.J. Noh, B.E. Smith, S. Jeong, Brief Communication: Sudden drainage of a subglacial lake beneath the Greenland Ice Sheet, The Cryosphere, 9,103-108, doi:10.5194/tc-9-103-2015

http://www.the-cryosphere.net/9/103/2015/tc-9-103-2015.html

Abstract. We report on the appearance of a 2 km wide, 70 m deep circular depression located 50 km inland of the southwestern margin of the Greenland Ice Sheet that provides the first direct evidence for concentrated, long-term storage, and sudden release, of meltwater at the bed. Drainage of the lake may have been triggered by the recent increase in meltwater runoff. The abundance of such lakes and their potential importance to the ice sheet's hydrologic system and flow regime remain unknown.

See also:
http://www.cbsnews.com/news/the-case-of-greenlands-disappearing-lakes/
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Re: what's new in Greenland ?
« Reply #67 on: January 21, 2015, 11:41:16 PM »
Thanks, ASLR. I think I located the little bastard on the 10072012 MODIS tile in my CAD-grid. It is high up in the bare ice slope, about 8 km from the snow-line further up. From that line upwards, the melting snow slope continued for another 70 km. G.Earth indicates a height of 1850 m1 for the 'dry' snow line. The 'little bastard' lies on 1350 m1 asl.
On MODIS there are lots of features like that.
I remember one of the posters on the blog having suggested that these 'swiss cheese' moulins could deliver a lot of dynamic warmth to the whole ice sheet depth. At the time, I suggested there could be a time when we may witness karst-like collapses. In this article I read a sort of confirmation. This could be a beginning.

sidd

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Re: what's new in Greenland ?
« Reply #68 on: January 22, 2015, 03:56:27 AM »
Re:MacGregor(2015)

small warning:
the nc file is 2.4 gig and the mat file is 1.5 gig. the first opens fine is qgis and is fascinating. octave crashes and burns on the latter. qgis should open hdf5 but i havent bothered bcoz nc is all good.

o that i had time

sidd

AbruptSLR

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Re: what's new in Greenland ?
« Reply #69 on: January 22, 2015, 10:20:15 PM »
The following reference discusses how the GIS was formed:

Bernhard Steinberger, Wim Spakman, Peter Japsen, Trond H. Torsvik, (2014), "The key role of global solid-Earth processes in preconditioning Greenland's glaciation since the Pliocene", Terra Nova, DOI: 10.1111/ter.12133
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A-Team

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Re: what's new in Greenland ?
« Reply #70 on: January 23, 2015, 03:31:34 PM »
how tectonic motion northward of Greenland set the stage for ice sheet formation

True polar wander is an interesting idea, slippage relative to the mantle followed by readjustment of the rotation axis to the new moment of inertia. I have to say that a wide swath of geologists do not subscribe to the coincidence of the Iceland hot spot sitting on the center of a rifting axis. In this view, Iceland is not a conventional mantle plume (a slippery term with dozens of published definitions), has produced no track of islands like other hotspots, was never under Greenland influencing its geothermal regime, and indeed is unsuitable for inclusion inthe hot spot coordinate reference system.

The closing of the Panama Strait at 2.5 myr end-Pliocene is the 800 lb gorilla here in terms of oceanic circulation -- there had to have been massive consequences, along the lines of Tasman Strait much earlier. Note once  over-turned geology exposed at the canal was revealed by recent field work, oft-claimed discrepancies have evaporated.

The northern hemisphere goes 400 myr without significant glaciation, then a one-off closing of the straits (requiring major equatorial heat redistribution mechanisms), and right away the glaciation cycles commence. Coincidence? No thanks.

The authors here desperately needed to discuss equatorial glaciers such as Rwenzori, Kilimanjaro and the Andes that do have glaciers despite their low latitude plus all the regions in Siberia, Alaska and Canada that don't have glaciers despite Greenlandic latitudes.
« Last Edit: January 24, 2015, 12:59:28 PM by A-Team »

A-Team

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Re: what's new in Greenland ?
« Reply #71 on: January 23, 2015, 03:41:54 PM »
Here's a youtube release of NASA's new visualization of MacGregor 2015. It comes with a voice-over narration (rather basic from our perspective).

https://www.youtube.com/watch?v=u0VbPE0TOtQ
 
"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 [dead link]"


That link should be http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4249&button=recent where much more detailed information, the text of the narration etc etc are provided. Very much worth a look. Hopefully meant as artwork, look at that same image reprocessed for isochrons.)
« Last Edit: January 23, 2015, 06:28:58 PM by A-Team »

Jim Hunt

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Re: what's new in Greenland ?
« Reply #72 on: January 23, 2015, 08:48:01 PM »
I think the NSIDC have been plagiarising ASIF techniques! See their "2014 melt season in review" then scroll to the bottom. The abstract is as follows:

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.




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Re: what's new in Greenland ?
« Reply #73 on: January 23, 2015, 11:02:02 PM »
Below I took some screen grabs from the Goddard animation. The image shows three frames of the Greenland ice sheet slumping from the summit to the sea. This gives you some idea what models calculate but never display. It is done much better in the actual video.

The other image displays for the very first time the highly contoured subglacial thickness surfaces, starting with the usual contemporary view, followed by stripping off Holocene ice to reveal the 11.7 kyr surface, and finishing with the Eemian ice which is much more extensive than previously thought.

Again, we don't need this fancy perspective view and hopefully we can replace it soon with a higher resolution scientific grayscale, from which anyone can produce their own bump map in a few seconds. The reason for going scientific is the asymmetry: it's all but impossible to recover underlying data from a perspective.

There is some confusion here between portraying the isochronal surface by its elevation relative to sea level (or bottom of NGRIP) vs portraying its thickness, which will differ according to ± departure of bedrock topography from sea level. The former smooth surface is what you'd see in an ice core; the latter bumpy surface is wanted for gravitational driving stress.

The 'age volume' is an interesting concept. This takes any two dated surfaces and computes the volume of ice between them over all Greenland. Fitting this data to per-year volume then measures net retained accumulation over the 100 kyr available. The newtonian volume integrals can be done in Gimp simply by subtracting the two grayscale surface elevations and summing via the histogram and mean value theorem.

A good quote from lead author MacGregor:
“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

This is neat quote too:
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.

MacGregor, J.A., J. Li, J.D. Paden, G.A. Catania, G.D. Clow, M.A. Fahnestock, S. Gogineni,
R.E. Grimm, M. Morlighem, S. Nandi, H. Seroussi and D.E. Stillman,
Radar attenuation and temperature within the Greenland Ice Sheet,
Journal of Geophysical Research Earth Surface (same journal, in press)
 
MacGregor, J.A., W.T. Colgan, M. Morlighem, M.A. Fahnestock, G.A. Catania, J.D. Paden and S. Gogineni
Holocene deceleration of the Greenland Ice Sheet
Journal not specified  (in review)
« Last Edit: January 24, 2015, 01:58:03 PM by A-Team »

A-Team

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Re: what's new in Greenland ?
« Reply #74 on: January 24, 2015, 01:45:30 PM »
AbruptSLR quite rightly calls our attention to one of the two Greenland lake stories that appeared Thursday, namely 'Sudden drainage of a subglacial lake beneath the Greenland Ice Sheet' which is open source at http://www.the-cryosphere.net/9/103/2015/tc-9-103-2015.html

The other paper -- and even its graphics -- are paywalled but Andrea Thompson wrote up a nice review at
http://www.climatecentral.org/news/surprise-lake-sheds-light-on-underbelly-of-greenland-ice-18580

It's all about heat: whether solar and atmospheric energy (meltwater) runs off harmlessly into the sea as surface rivers or efficient under-glacier tunnels, or stays behind on, in or under the ice sheet thus softening or lubricating it to faster calving (sea level rise). Since the meltwater is already at 0º C, it comes down to glacial capture (or not) of latent heat.

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.

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.

The first page of the article is offered by readcube, the whole article for $4. Helpfully, supplemental data is free.
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14116.html

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Re: what's new in Greenland ?
« Reply #75 on: January 24, 2015, 02:01:36 PM »
These unplugging happens now and then, there was a huge one prior to 1984 in North Greenland:
https://forum.arctic-sea-ice.net/index.php/topic,335.msg6224.html#msg6224
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Re: what's new in Greenland ?
« Reply #76 on: January 25, 2015, 10:36:06 AM »
The Steensby Depression:

The above mentioned depression / unplugging from 1984 can still be seen, if any interest we might be able to convince Wipneus to convert a landsat image from 2014 to real colors and higher resolution?

« Last Edit: January 25, 2015, 01:35:01 PM by Espen »
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Re: what's new in Greenland ?
« Reply #77 on: January 25, 2015, 01:32:49 PM »
We should be paying some attention to the Dec 2014 release from the INTIMATE (INTegration of Ice-core, MArine and TErrestrial records) project. Although  committee proceedings and protocols are tediously pedantic, they do amount to careful expert review of the timing and best-practice nomenclature for the major climatic and volcanic events that show up in the Greenland ice cores (and sometimes in Antarctica's as well), and by extension explain some aspects of radar stratigraphy as pulled together in MacGregor 2015.

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.


The first image below from Rasmussen 2014 only shows about 10% of their overall timeline, which extends back from 8-123 kyr. The table is very clumsily done in the pdf but is promised soon in xls format at the fifth link; a small part of it is shown in the second image.

The Blockley chronology focuses on tephra events of the last 8-60 kyr; these will correspond better to ice core conductivity (~radar permitivity) and so the calcium dust trace might be fitted to the MacGregor 2015 isochronal dating scheme. The 18O line could tie in to englacial temperature profiles which may have also been determined in a second MacGregor article "Radar attenuation and temperature within the Greenland Ice Sheet" caught up in peer review.

http://forum.arctic-sea-ice.net/index.php/topic,984.msg36237.html#msg36237 initial chronology
http://tinyurl.com/lsn5hkk Rasmussen 2014
http://tinyurl.com/opwrmw4 Seierstad 2014
http://tinyurl.com/k46z598 Blockley 2014
http://www.iceandclimate.nbi.ku.dk/data Data Archive
« Last Edit: January 25, 2015, 02:01:31 PM by A-Team »

A-Team

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Re: what's new in Greenland ?
« Reply #78 on: January 27, 2015, 09:05:08 PM »
The 4th new article on Greenland paleo-tephra seems to be paywalled but I found a copy soon enough via ResearchGate, which is quite a nice way to get in touch with authors. This issue in Quaternary Science Reviews is incredibly convenient for us, coming as it does at the same time as the newly dated radarstratigraphy tied in to the same ice cores in MacGregor 2015.

If someone reading this post has a knack for extracting clean excel text files out of these nasty journal pdfs, that would be a great public service to grab the ones above and below so we have a decent searchable chronology of the Greenland ice sheet.

A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25e45 ka b2k
Quaternary Science Reviews
AJ Bourne 2014
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.

I 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.

In practice this means plotting percent weights of sodium plus potassium oxides vs silicon dioxide, titanium oxide vs aluminum oxide, ferrous oxide vs calcium oxide (lime), and FeO/Ti02 vs SiO2 as in Fig 5, 6, and 7.

There is no way of knowing a priori which combinations (if any) would have the necessary resolving power and no doubt many other things were tried but didn't work out.

The temptation for me is to plot the data in the higher dimensional spaces for which these biplots are just sections (projections on axial pairs), then do principal component analysis to bring it all back to dimension 2 or 3. Or go with support vector machines. Either would give much better separation of volcanoes and higher statistical confidence. But I would say they didn't need anything more than their biplots here.

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Re: what's new in Greenland ?
« Reply #79 on: February 06, 2015, 12:45:34 AM »
(Already known on this forum)
Greenland’s hidden meltwater lakes store up trouble
http://www.theguardian.com/environment/2015/feb/05/greenlands-hidden-meltwater-lakes-store-up-trouble

“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.”
« Last Edit: February 06, 2015, 09:14:06 AM by Laurent »

A-Team

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Re: what's new in Greenland ?
« Reply #80 on: February 06, 2015, 02:52:22 AM »
Save yourself the €34.95 and get the Applegate full text at http://tinyurl.com/oadcjlj -- this is quite cool how younger scientists have taken to ResearchGate to get their work out there where everyone can access it, even as the older ones still defer to journal MBAs.

If you wanted to dig into the modelling, this research was based on open source Sicopolis which has its own web page: http://www.sicopolis.net/

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.
This seems bizarre at first in that 3 of the outputs are already known for Greenland and the others don't seem subject to experimental validation anytime soon. I suppose the idea is to keep tweaking inputs until something emerges that matches the outputs.

Here you will find Cuffey & Paterson 4th edition, a required text for every budding glaciologist ($75 at Amazon), providing a blunt cautionary statement already on page 5 about accidental agreements (non-uniqueness of solutions):

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.
« Last Edit: February 06, 2015, 05:02:39 PM by A-Team »

Sleepy

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Re: what's new in Greenland ?
« Reply #81 on: February 22, 2015, 05:42:26 AM »
I certainly appreciate when I can access the papers for free, as their much appreciated work is about my home and my kids future, earth.

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Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #83 on: July 15, 2015, 08:29:58 PM »

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Andreas Muenchow

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Re: what's new in Greenland ?
« Reply #86 on: July 16, 2015, 01:55:12 AM »
Open Water != Melting

Differential advection (divergence) of ice can and does cause open water.
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Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #87 on: July 19, 2015, 10:26:06 PM »
Colgan et al on potential Thermal Viscous Collapse of GIS:
http://onlinelibrary.wiley.com/doi/10.1002/2015EF000301/full

Abstract
We explore potential changes in Greenland ice sheet form and flow associated with increasing ice temperatures and relaxing effective ice viscosities. We define “thermal-viscous collapse” as a transition from the polythermal ice sheet temperature distribution characteristic of the Holocene to temperate ice at the pressure melting point and associated lower viscosities. The conceptual model of thermal-viscous collapse we present is dependent on: (1) sufficient energy available in future meltwater runoff, (2) routing of meltwater to the bed of the ice sheet interior, and (3) efficient energy transfer from meltwater to the ice. Although we do not attempt to constrain the probability of thermal-viscous collapse, it appears thermodynamically plausible to warm the deepest 15% of the ice sheet, where the majority of deformational shear occurs, to the pressure melting point within four centuries. First-order numerical modeling of an end-member scenario, in which prescribed ice temperatures are warmed at an imposed rate of 0.05 K/a, infers a decrease in ice sheet volume of 5 ± 2% within five centuries of initiating collapse. This is equivalent to a cumulative sea-level rise contribution of 33 ± 18 cm. The vast majority of the sea-level rise contribution associated with thermal-viscous collapse, however, would likely be realized over subsequent millennia.

Tor Bejnar

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Re: what's new in Greenland ?
« Reply #88 on: July 21, 2015, 03:51:54 PM »
See Discovery News:  Weakened Solar Activity Could Speed Greenland Ice Melt

The following is from E&E’s publishing service – subscription required
http://www.eenews.net/climatewire/2015/07/21/stories/1060022132

"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.
...

Arctic ice is healthy for children and other living things.

A-Team

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Re: what's new in Greenland ?
« Reply #89 on: July 21, 2015, 05:21:19 PM »
The article is paywalled but it takes but minutes to get a copy by email from the AGU secretariat. Temperatures and argon and nitrogen isotopes at NGRIP and GISP2 have been determined previously but here they added NGRIP2. These are not new firn cores but the top 400 m of main cores. It's not clear whether this entailed destructive sampling.

The resolution sounds somewhat sketchy (10 years per sample) and the time span a bit short at 2100 years out of 10,700. I would like to have seen more predictions, say of Renland profiles. Renland may be more informative than these summit ridge sites being adjacent to the North Atlantic conditions under discussion.

This is a sophisticated paper that is well worth reading past the counter-intuitive headlined aspects of AMOC  and Greenland temperatures. However that involves also reading all of the 17 MB supplemental as well as 6 previous Kobashi papers in this series.

The authors here do not delve into future variations in total solar irradiance, though the publisher may be playing off the Sarkova PCA dynamo paper to generate publicity. That paper is actually from November, 2014 which in turn is a re-hash of a 2012 paper. These are interesting technically but attracted minimal interest; the furor came from her recent meeting talk and careless comments about climate, a field in which she is unqualified, unfamiliar and unpublished. The Kobashi paper shows how complicated the latter analysis really is.

https://www.researchgate.net/profile/Valentina_Zharkova/publications free full text

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064764/full?campaign=wlytk-41855.5282060185

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.

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.

http://news.discovery.com/earth/global-warming/weakened-solar-activity-could-speed-up-greenland-ice-melt-150717.htm

The green shaded area (late 20th century) is when the modern solar maximum had strong negative influence (red circle) on the Greenland temperature.
« Last Edit: July 22, 2015, 05:44:44 PM by A-Team »

Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #90 on: July 23, 2015, 12:06:32 PM »
New paper on Greenland ice velocities:
http://www.mdpi.com/2072-4292/7/7/9371

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Re: what's new in Greenland ?
« Reply #91 on: July 23, 2015, 06:40:06 PM »
While somewhat old news, the following link leads to an Arctic Report Card on the Greenland Ice Sheet through the end of 2014:

http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html
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Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #92 on: July 27, 2015, 05:14:03 PM »
Furst et al 2015 find a maximum 16-17 cm of SLR contribution from GIS by 2100 under RCP8.5:
http://www.the-cryosphere.net/9/1039/2015/tc-9-1039-2015.pdf

Haven't read the paper yet, so wondering what their assumptions are.
« Last Edit: July 27, 2015, 05:20:41 PM by Lennart van der Linde »

Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #93 on: July 27, 2015, 05:48:18 PM »
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

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.

Stephen

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Re: what's new in Greenland ?
« Reply #94 on: July 29, 2015, 02:50:05 PM »
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

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.


But with 6-8C of warming will there be anyone left alive to measure it?
The ice was here, the ice was there,   
The ice was all around:
It crack'd and growl'd, and roar'd and howl'd,   
Like noises in a swound!
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Lennart van der Linde

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Re: what's new in Greenland ?
« Reply #95 on: July 29, 2015, 03:32:42 PM »
Good question. Maybe a few million/billion people would still be around...

cats

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Re: what's new in Greenland ?
« Reply #96 on: July 29, 2015, 11:59:35 PM »
This project - http://www.nature.com/news/nasa-launches-mission-to-greenland-1.18085?WT.mc_id=TWT_NatureNews sounds interesting and should produce some interesting data. 
Excerpt:
"Called Oceans Melting Greenland (OMG), the US$30-million NASA project will help scientists to predict the future of the Greenland ice sheet, which holds enough water to boost sea levels by around 6 metres and already seems to be melting more rapidly in response to increasing air temperatures. But it is not clear how much the oceans affect the rate of melting along the island’s edges, which depends on poorly known variables such as how warm, saline water interacts with the glaciers."

notjonathon

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Re: what's new in Greenland ?
« Reply #97 on: July 30, 2015, 02:35:33 AM »
re: OMG

NASA meets The Onion?

Some dark humor over there.

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Re: what's new in Greenland ?
« Reply #98 on: August 01, 2015, 07:38:26 AM »
lurking about byrd polar research center bprc.osu.edu brought me to this paper by the redoubtable Ellen Mosley-Thompson, Howat and others

snow turning to ice in greenland, reduced melt buffer and such

" ... these huge ice reservoirs are the result of an intense melting process of the same order of magnitude as the total mass imbalance of the GrIS ... "

thats about 400 GT

http://www.the-cryosphere.net/9/1203/2015/tc-9-1203-2015.html

open access

many nice videos at bprc too

sidd

Lennart van der Linde

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Re: .what's new in Greenland ?
« Reply #99 on: August 05, 2015, 11:19:50 PM »
Here an attempt by Calov et al 2015 to model GIS in the Eemian:
http://www.the-cryosphere.net/9/179/2015/tc-9-179-2015.pdf

They find an estimated average contribution of about 1.4m from GIS to Eemian-SLR (range 0.6-2.5m).
« Last Edit: August 05, 2015, 11:25:11 PM by Lennart van der Linde »