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Author Topic: What's new in Greenland?  (Read 113768 times)

solartim27

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« Last Edit: January 18, 2018, 11:01:42 PM by solartim27 »
FNORD

AbruptSLR

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Re: What's new in Greenland?
« Reply #301 on: February 09, 2018, 06:29:17 PM »
The linked reference provides a nice review of outlet glaciers in northern Greenland:

Hill, E. A., Carr, J. R., Stokes, C. R., and Gudmundsson, G. H.: Dynamic changes in outlet glaciers in northern Greenland from 1948 to 2015, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-17, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-17/

Abstract. The Greenland Ice Sheet (GrIS) is losing mass in response to recent climatic and oceanic warming. Since the mid-1990s, marine-terminating outlet glaciers across the GrIS have retreated, accelerated and thinned, but recent changes in northern Greenland have been comparatively understudied. Consequently, the dynamic response (i.e. changes in surface elevation and velocity) of these outlet glaciers to changes at their termini, particularly calving from floating ice tongues, remains unknown. Here we use satellite imagery and historical maps to produce an unprecedented 68-year record of terminus change across 18 major outlet glaciers and combine this with previously published surface elevation and velocity datasets. Overall, recent (1995–2015) retreat rates were higher than at any time in the previous 47 years, but change-point analysis reveals three categories of frontal position change: (i) minimal change followed by steady and continuous retreat, (ii) minimal change followed by a switch to a period of short-lived rapid retreat, (iii) glaciers that underwent cycles of advance and retreat. Furthermore, these categories appear to be linked to the terminus type, with those in category (i) having grounded termini and those in category (ii) characterised by floating ice tongues. We interpret glaciers in category (iii) as surge-type. Glacier geometry (e.g. fjord width and basal topography) is also an important influence on the dynamic re-adjustment of glaciers to changes at their termini. Taken together, the loss of several ice tongues and the recent acceleration in the retreat of numerous marine-terminating glaciers suggests northern Greenland is undergoing rapid change and could soon impact on some large catchments that have capacity to contribute an important component to sea level rise.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: What's new in Greenland?
« Reply #302 on: February 20, 2018, 09:25:57 AM »
That Hill paper is brilliant. Check out figs 7,8,9. Open access.

sidd

Espen

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Re: What's new in Greenland?
« Reply #303 on: February 20, 2018, 10:20:29 PM »
That Hill paper is brilliant. Check out figs 7,8,9. Open access.

sidd

Not so in my oppinion according to the paper Steensby Gletscher should be advancing, that is not true the glacier retreated more than 20 km over the last decade??
Have a ice day!

sidd

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Re: What's new in Greenland?
« Reply #304 on: February 21, 2018, 05:36:56 AM »
That figure is odd considering this statement on pg 8:

"Steensby Glacier underwent minimal change during the study period (1 m a -1 : 1948–2015), but
with a high rate of retreat from 1978 to 2015 (-366 m a -1 )."

Fig 4 shows Steensby at +104m/yr till 2010 or later, but then retreating at 3Km/yr

Perhaps you should post a comment there. the paper is still in discussion, i think.

sidd

P.S. : I think i figured it out fig3 is the average from 1948, and the rapid recent retreat has not swung the average yet.
« Last Edit: February 21, 2018, 08:48:45 AM by sidd »

sidd

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Re: What's new in Greenland?
« Reply #305 on: March 01, 2018, 12:30:00 AM »
Nice paper by Joughin, Smith and Howat with new velocity maps.

"It is unclear whether external forcing, internal dynamics, or some combination of both have contributed to the changes in terminus extent that have produced the recent slowdown. Temperature records from the nearby coastal station at Egedesminde 20 indicate that 2017 was the second coldest year, behind 2015, in the 21 st Century (GISS, 2018). Thus, one plausible hypothesis is that the recent colder temperatures may have contributed to the advance and slowdown, although if there were cooler water at the terminus it could have played a role as well. Whether this slowdown could reduce summer thinning and increase winter thickening sufficiently to stabilize the glacier over scales of years to decades is unclear."

...

"If the recent slowdown is not the beginning of a period of stabilization, then the terminus of Jakobshavn Isbrae likely will continue to retreat at least 60 km inland until it recedes from the trough’s deeper parts (Joughin et al., 2012)"

Open access. Read the whole thing.

doi: 10.5194/tc-2018-40

sidd


sidd

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Re: What's new in Greenland?
« Reply #306 on: March 03, 2018, 02:54:16 AM »
Bamber and the usual suspect have a paper out on Arctic freshwater flux:

doi: 10.1002/2017JC013605

"The cumulative freshwater flux anomaly exceeded 6300±316 km^3 by 2016. This is roughly twice the estimate of a previous analysis that did not include glaciers and ice caps outside of Greenland and which extended only to 2010. From 2010 onward, the total freshwater flux is about 1300 km 3 /yr, equivalent to 0.04 Sv, which is roughly 40% of the estimated total runoff to the Arctic for the same time period. Not all of this flux will reach areas of deep convection or Arctic and Sub-Arctic seas. We note, however, that the largest freshwater flux anomalies, grouped by ocean basin, are located in Baffin Bay and Davis Strait ... "

"The total cumulative FWF anomaly is close to reaching a value where it will be comparable to the interannual
variability in FWF driven by other processes in the climate system [Boning et al., 2016]."

I attach a figure

sidd

AbruptSLR

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Re: What's new in Greenland?
« Reply #307 on: March 14, 2018, 11:02:48 PM »
If the findings of the linked reference are correct then "chain-reactions of fast draining lakes" could threaten the stability of key portions of Greenland's ice sheet over the coming 50 years:

Poul Christoffersen et al, Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture, Nature Communications (2018). DOI: 10.1038/s41467-018-03420-8

http://www.nature.com/articles/s41467-018-03420-8

Abstract: "Supraglacial lakes on the Greenland Ice Sheet are expanding inland, but the impact on ice flow is equivocal because interior surface conditions may preclude the transfer of surface water to the bed. Here we use a well-constrained 3D model to demonstrate that supraglacial lakes in Greenland drain when tensile-stress perturbations propagate fractures in areas where fractures are normally absent or closed. These melt-induced perturbations escalate when lakes as far as 80 km apart form expansive networks and drain in rapid succession. The result is a tensile shock that establishes new surface-to-bed hydraulic pathways in areas where crevasses transiently open. We show evidence for open crevasses 135 km inland from the ice margin, which is much farther inland than previously considered possible. We hypothesise that inland expansion of lakes will deliver water and heat to isolated regions of the ice sheet’s interior where the impact on ice flow is potentially large."

See also:

Title: "Chain reaction of fast-draining lakes poses new risk for Greenland ice sheet"

https://phys.org/news/2018-03-chain-reaction-fast-draining-lakes-poses.html

Extract: "A growing network of lakes on the Greenland ice sheet has been found to drain in a chain reaction that speeds up the flow of the ice sheet, threatening its stability."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

litesong

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Re: What's new in Greenland?
« Reply #308 on: March 16, 2018, 05:26:27 PM »
Yes, that is a lollapalooza! I just read about it from this Science Daily: https://www.sciencedaily.com/releases/2018/03/180314092305.htm
But I see I'm already late, here. ha ha ha
It almost sounds like the stress-tensor theory they expounded in our 1970's aeronautical structures classes.
« Last Edit: March 16, 2018, 06:01:41 PM by litesong »

gerontocrat

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Re: What's new in Greenland?
« Reply #309 on: March 20, 2018, 10:52:25 AM »
http://spacenews.com/iridium-raising-new-debt-to-cover-late-aireon-payments/

Iridium raising new debt to cover late Aireon payments
by Caleb Henry — February 26, 2018


You might be asking what on earth has Iridium's debts got to do with Greenland ?

Once upon a time there was the GRACE project (US & Germany) that gave us the data on ice mass loss in Greenland (and Antarctica and loads of other data used in more than 6000 scientific papers). It lasted much longer than its design life but NASA finally took it off life support in January 2017.

Do not despair - the new improved GRACE Follow-on project is due to happen this spring (and the specs look great). But the private sector are doing the launch with Iridium satellites also involved. Things have got messy - see below.

This project has major importance. The data will be (amongst other things) the definitive record of ice mass change of the ice-sheets, eliminating uncertainty, speculation and denial.

Quote

WASHINGTON — A company that fleet operator Iridium formed to help finance its second-generation satellite constellation is taking longer than expected to pay Iridium back for carrying its sensor network to orbit.

McLean, Virginia-based Iridium said Feb. 22 that to avoid counting on aircraft-tracking startup Aireon for liquidity, Iridium went back to its lenders to raise additional debt to finish the $3 billion Iridium Next constellation it’s in the midst of deploying.

Next SpaceX launch in late March

Iridium CEO Matt Desch said the successful Feb. 22 launch of a SpaceX Falcon 9 from Vandenberg Air Force Base cleared the way for greater schedule certainty with Iridium Next, which is launching entirely from the California facility. So far SpaceX has completed four Falcon 9 launches for Iridium, and has four more to go, though the original launch campaign was supposed to have been completed in 2017.

The fifth Iridium Next launch will likely occur March 29, he said. Subsequent missions should follow every five to six weeks until the constellation is complete, he said. Each launch carries 10 satellites at a time, with the exception of the sixth launch, which will carry five Iridium Next satellites and two U.S.-German science satellites called GRACE-FO.

The GRACE-FO, or Gravity Recovery and Climate Experiment Follow-On satellites, were originally supposed to launch on a Dnepr rocket through the Russian-Ukrainian joint venture Kosmotras, but the mission never happened. Iridium had two satellites slated to launch on Dnepr as well, but booked a shared Falcon 9 after Russian red tape left the launch, once forecast for 2015, on indefinite hold.

What a complicated world we live in. ("Oh! what a tangled web we weave" Sir Walter Scott 1808 - not the Bard).

PS Ice-Sat 2 - will look at ice thickness - launch in September 2018 (We hope). A definitive measurement of ice thickness would be a big plus?
http://environmentalresearchweb.org/cws/article/news/70881
« Last Edit: March 20, 2018, 10:59:18 AM by gerontocrat »
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sidd

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Re: What's new in Greenland?
« Reply #310 on: March 29, 2018, 08:08:36 PM »
Paper by Graeter et al on increasing melt in Greenland over the last twenty years. They looked at cores from the percolation zone, and it is clear from the ice left behind by melt evetns that melt frequency has been increasing over the last two decades. I attach fig 1.

doi:10.1002/2017GL076641

sidd

gerontocrat

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Re: What's new in Greenland?
« Reply #311 on: April 11, 2018, 02:21:03 PM »
GRACE FOLLOW-ON LAUNCH AT LAST -

https://www.prnewswire.com/news-releases/nasa-invites-media-to-launch-of-grace-follow-on-spacecraft-300627660.html

Quote
GRACE-FO will launch as part of a commercial rideshare mission with five Iridium Communications Inc. satellites aboard a SpaceX Falcon 9 rocket. The Iridium-6/GRACE-FO launch is scheduled for no earlier than 1:03 p.m. PDT (4:03 p.m. EDT) May 19 from Vandenberg Air Force Base in California.

Read all about it on https://gracefo.jpl.nasa.gov/ from the jet propulsion lab. Also about ICE-SAT-2
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gerontocrat

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Re: What's new in Greenland?
« Reply #312 on: April 18, 2018, 11:43:14 AM »
A paper on Glacier Calving in Greenland from October 2017. Certainly improved my understanding of the subject.
https://link.springer.com/content/pdf/10.1007%2Fs40641-017-0070-1.pdf

And an older one from 2012 also giving me a bit more insight.
http://www.pnas.org/content/109/49/19934
Mapping Greenland’s mass loss in space and time

See map below - how to find an up-to-date equivalent?


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