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Author Topic: What's new in Greenland?  (Read 68235 times)

sidd

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Re: What's new in Greenland?
« Reply #200 on: September 21, 2016, 11:33:40 PM »
GRACE estimates for GIS mass loss are 10% too low because of flawed GIA model.  Many usual suspects on the author list. Open access. Read all about it.

doi: 10.1126/sciadv.1600931

Lennart van der Linde

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Re: What's new in Greenland?
« Reply #201 on: September 22, 2016, 06:35:07 AM »
Thanks, sidd.
It's about 7-8 percent more melt between 2003-2013 than thought earlier, according to:
https://www.sciencedaily.com/releases/2016/09/160921145338.htm

Here's the full article by Khan et al 2016,Geodetic measurements reveal similarities between post–Last Glacial Maximum and present-day mass loss from the Greenland ice sheet:
http://advances.sciencemag.org/content/2/9/e1600931.full

Abstract
Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.

sidd

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Re: What's new in Greenland?
« Reply #202 on: October 31, 2016, 11:07:34 PM »

charles_oil

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Re: What's new in Greenland?
« Reply #203 on: November 04, 2016, 10:17:15 PM »
At NSIDC there is now an interactive "chartic" style graph for the melting on Greenland - sadly its arrived just when they have stopped recording the melt so we wont catch any surprises in the current weirdly high temperatures.

As its real daily data rather than smoothed 5 day data the bands are a bit wide and rugged - so its harder to see what is going on than with the Chartic area/ extent one.

http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/ - would this be a handy link for the ASI Graphs section ?

Anne

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Re: What's new in Greenland?
« Reply #204 on: January 02, 2017, 11:25:42 PM »
Using Landsat to Take the Long View on Greenland's Glaciers

A new publicly accessible data portal for analysing changes in outlet glacier flow velocities. EOS article from 29 December:
<snip>We based our project on more than 37,000 optical images collected by multiple sensors aboard the U.S. Geological Survey (USGS) and NASA’s Landsat satellites. The data span the period between 1972, when Landsat 1 was launched, and 2015, using data from Landsat 8 (launched in 2013), although most of the Landsat scenes were acquired after 1998.

We will continue to extend the database using new scenes recorded by the ongoing Landsat 7 and 8 missions. The USGS Landsat Global Archive Consolidation (LGAC) will add even more scenes, providing access to Landsat data that are archived at individual international ground stations [Wulder et al., 2016]. For Greenland, this could provide a considerable number of scenes from Landsat 4 and 5, dating back to 1982.

These additional images are valuable for extending the time span of the velocity time series. This greater time span is particularly important for inferring flow velocity variations that occur within the span of one season, and it may help to close observation gaps that occurred before 1999, when Landsat 7 was launched. Moreover, in regions of extensive cloud coverage, collecting Landsat scenes over a longer time span increases the chance of obtaining cloud-free data.

Enhanced Data Processing Provides a Clearer Picture
For 302 glaciers all around Greenland, we have processed more than 100,000 flow velocity fields from 1972 to 2012. We have extended this processing to include velocity fields for about 50 major glaciers up to 2015 so far.

By adding a quality flag that indicates the reliability of the data, we reduced the number of existing velocity fields with extensive outliers. We used an outlier detection strategy that compared the differences between each observed velocity product and a theoretically derived velocity field to compile the statistical parameters for our evaluation. Altogether, we have made more than 40,000 flow velocity fields accessible so far, and we continue to add new velocity fields as we process more data.

Rosenau et al. [2015] described a number of steps included in the processing procedure. We have improved the correction for tilt and terrain effects (orthorectification) using the Global Digital Elevation Map Version 2 (GDEM V2) from NASA’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The improved orthorectification step, in particular, facilitates the usage of overlapping scenes from orbits that are not repeat passes. The ability to include these additional scenes provides a much higher effective sampling rate than would be provided by repeat-pass sampling, which is limited to the repeat orbit of 16 days (Landsat 4 to 8 ) or 18 days (Landsat 1 to 3).

In 2003, a small pair of mirrors (the scan line corrector) aboard Landsat 7 failed, introducing data gaps as well as small shifts between the scan lines. We applied a destriping correction to mitigate the impact on the resulting velocity fields. In addition, we removed outliers using an adaptive, recursive filter approach. The combination of all these improvements leads to higher accuracy of the inferred velocity fields.

Long-Term and Seasonal Trends in Flow Velocity
The long time span covered by the Landsat scenes allows us to determine long-term flow velocity trends. The high temporal resolution lets us analyze seasonal flow velocity variations of numerous outlet glaciers. However, the pattern of temporal and spatial distributions of the flow velocity changes is not uniform (Figure 1). The monitoring system provides a powerful tool to examine the flow velocity pattern throughout time and space, and we have detected an acceleration pattern for a number of outlet glaciers.
More at the link: https://eos.org/project-updates/using-landsat-to-take-the-long-view-on-greenlands-glaciers
and at Technische Universität Dresden’s site here: https://data1.geo.tu-dresden.de/flow_velocity/

Shared Humanity

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Re: What's new in Greenland?
« Reply #205 on: January 20, 2017, 01:24:17 AM »
Wasn't sure where to post this photo of a melt lake on Greenland but decided to post it here. The photo came, not from a science study but as more of an art project. The link to more photos is here.

https://www.theguardian.com/artanddesign/2017/jan/19/what-should-be-pristine-white-is-littered-with-blue-timo-liebers-arctic-photography

This one interested me because of what it suggests about these melt lakes. The fragmented floes look like something you would see in the CAB during the height of the melt season and suggests that this lake does not freeze completely in the winter. I wonder how many melt lakes are like this?

Milret2

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Re: What's new in Greenland?
« Reply #206 on: February 11, 2017, 07:49:58 AM »
I just found this in today's Washington Post, am not entirely sure where the best place to put it is, and am not sure I know how to link so feel free to move it if I link properly but in a poor area and let me know if the link is bad.

A project started by NASA five years ago is starting to pay off. It is called OMG for "Oceans are Melting Greenland" and it is basically trying to see what temperature differentials are doing to underwater glacier masses at various levels. So far ... does not look very good but not enough data has been observed and I doubt that the current administration will allow much more to be collected.

Will try to leave a link here >>http://wapo.st/2lyasOz?tid=ss_mail<<

oren

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Re: What's new in Greenland?
« Reply #207 on: February 11, 2017, 11:58:48 AM »
I just found this in today's Washington Post, am not entirely sure where the best place to put it is, and am not sure I know how to link so feel free to move it if I link properly but in a poor area and let me know if the link is bad.

A project started by NASA five years ago is starting to pay off. It is called OMG for "Oceans are Melting Greenland" and it is basically trying to see what temperature differentials are doing to underwater glacier masses at various levels. So far ... does not look very good but not enough data has been observed and I doubt that the current administration will allow much more to be collected.

Will try to leave a link here >>http://wapo.st/2lyasOz?tid=ss_mail<<

The link worked for me with a slight modification http://wapo.st/2lyasOz

Tor Bejnar

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Re: What's new in Greenland?
« Reply #208 on: February 11, 2017, 04:04:48 PM »
Alas, it wasn't started 5 years ago - it started 2 years ago.  It was planned to be a 5-year study.
Here’s a figure that the scientists have produced, showing the overall flow of waters around the ice island:

...
“It’s too early” to run the model, said Mathieu Morlighem, a researcher at the University of California and the lead author of one of the papers presenting the accumulating data. “I think you need to wait another year or two, maybe more. It was not possible at all before OMG.”

Still, the recently published findings mark a start. Morlighem’s study, for instance, looked at the depth and shape of the seafloor near the fronts of and beneath numerous Greenland glaciers. The research shows that numerous glaciers extend deeper beneath the surface of the ocean than previously thought.

For instance, Store Glacier in northwestern Greenland (at around 70 degrees North latitude in the image above) starts at 400 meters (around 1,300 feet) deep where its front touches the ocean, and then plunges to depths as high as 1,000 meters deep (3,280 feet) farther inland — making it quite vulnerable to the ocean. Prior research, however, had suggested the glacier was much shallower.

The same was true of numerous other glaciers, which also appear more vulnerable than previously thought.

“OMG is transforming our knowledge of which glaciers are vulnerable to more warming or not,” Morlighem said. “So I wouldn’t say we have been surprised; it’s more, we had no idea, for many of these fjords, what they were looking like.”

Overall, the data are also showing that Greenland’s west coast is far more vulnerable, in general, than its east, Morlighem said.

The second study, meanwhile, examines ocean circulation around the Greenland coast and finds, strikingly, that between 68 degrees North latitude along the coast and 77 degrees North (see above), the deepest warm layer of Atlantic water cools from 3.5 degrees Celsius down to 2.5 degrees Celsius. Moreover, it does so in part because the water busily melts away at a large and deep glacier called Upernavik at 73 degrees North, which touches the ocean in 675 meter (over 2,000 foot) deep waters. The cold meltwater from the glacier spills into the ocean and, through mixing, cools the warm Atlantic water somewhat.

“The glaciers there are actively losing enough ice, and enough fresh water, that it’s important for the oceanography, and how the water changes as it goes up the west coast of Greenland,” says Willis. That in itself is proof that Greenland is melting quite a lot.

The big picture is that NASA’s new data suggest — that’s right — new vulnerabilities.

“Overall, together I think these papers suggest that the glaciers as a whole are more vulnerable than we thought they were,” Willis said. He says that, of course, with the aforementioned caveat that NASA is not ready yet to feed the data into a model that actually shows how this could play out over the decades of our future.
...
Arctic ice is healthy for children and other living things.

Carex

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Re: What's new in Greenland?
« Reply #209 on: February 12, 2017, 01:50:33 PM »
Is their coastal topography available as a map, or has it been incorporated into any other bedrock/till models??

johnm33

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Re: What's new in Greenland?
« Reply #210 on: February 13, 2017, 01:14:14 AM »

Carex

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Re: What's new in Greenland?
« Reply #211 on: February 13, 2017, 01:24:02 PM »
Since the OMG study is mapping glacier mouths and according to press reports finding more deep channels underlying more west coast glaciers, I was wondering if they had produced/or are planing to produce an updated coastal topography/bathymetric map.  It seems like it would be a first step on which to present the rest of their work.   

Susan Anderson

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Re: What's new in Greenland?
« Reply #212 on: February 13, 2017, 07:33:44 PM »
Here's an article linked from the OMG article, apologies if someone else has already posted it:
http://www.tos.org/oceanography/assets/docs/29-4_morlighem.pdf

Authors/official citation (above link provides full content):
Morlighem, M., E. Rignot, and J.K. Willis. 2016. Improving bed topography mapping of Greenland glaciers using NASA’s Oceans Melting Greenland (OMG) data. Oceanography 29(4):62–71, https://doi.org/10.5670/oceanog.2016.99.


sidd

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Re: What's new in Greenland?
« Reply #213 on: February 17, 2017, 07:45:17 PM »
doi: 10.1002/2016PA003014

Interesting paper about meltwater from Greenland reaching as far south as Bermuda during the Eemian (120-130Kyr BP)

"Shells from Rocky Bay and Grape Bay populate two distinct temperature ranges. Temperatures in Rocky Bay are 16 to 27°C, ~2°C lower than modern on average, whereas temperatures recorded by Grape Bay shells are 8 to 20°C, averaging ~10°C colder than modern "

"This second sea level rise event likely included contributions from both the Greenland and West Antarctic Ice Sheets [Dutton et al., 2015]. The southern portion of the Greenland Ice Sheet in particular underwent substantial melting between ~122 and ~119 ka [Colville et al., 2011; NEEM Community Members, 2013]. Given the location of Bermuda in the North Atlantic and the time constraints on deposition, it is possible, and perhaps likely, that the meltwater pulse recorded by Grape Bay shells came from rapid melting of the Greenland Ice Sheet."

"This possibility makes our results particularly relevant for the future of the North Atlantic. It appears that substantial and rapid melting occurred after thousands of years of sustained interglacial climate, when global ice volume was even smaller than today [Dutton and Lambeck, 2012]."

The possibility of MWP1A scale sea level rise is sometimes discounted since the volume of available ice to melt is smaller today. In that context, that last sentence is the killer, " ... when global ice volume was even smaller than today ... "

sidd

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Re: What's new in Greenland?
« Reply #214 on: April 01, 2017, 10:10:35 PM »
A new study just out about marginal Glaciers and Ice Caps (GICs) in Greenland, in which the authors managed to:

identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt−1, or ∼14% of the Greenland total.”


See more at: http://www.nature.com/articles/ncomms14730

sqwazw

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Re: What's new in Greenland?
« Reply #215 on: April 04, 2017, 04:23:22 AM »
NSIDC's greenland-today is back online for 2017. No action yet.

http://nsidc.org/greenland-today/

gerontocrat

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Re: What's new in Greenland?
« Reply #216 on: April 13, 2017, 02:56:55 PM »
NSIDC's greenland-today is back online for 2017. No action yet.

http://nsidc.org/greenland-today/


There has been a tiny bit of action. Look very carefully on Cumulative  Melt Days Jan 1 - Apr 11 at bottom SW corner and there are 2 light blue pixels !!!

DrTskoul

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Re: What's new in Greenland?
« Reply #217 on: April 13, 2017, 03:00:50 PM »
NSIDC's greenland-today is back online for 2017. No action yet.

http://nsidc.org/greenland-today/


There has been a tiny bit of action. Look very carefully on Cumulative  Melt Days Jan 1 - Apr 11 at bottom SW corner and there are 2 light blue pixels !!!



Yay... you pass the eye test...
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― Richard P. Feynman

Cate

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Re: What's new in Greenland?
« Reply #218 on: April 21, 2017, 04:59:39 PM »
NASA OMG blog by science communicator Laura Faye Tenebaum on Greenland: "A vast melting desert."

".....Over my headset, I can hear the pilots discussing the flight path with the instrument engineers. Out the window, I can see Greenland’s northernmost glaciers below us; white upon white upon white. They sure appear stable, still, enduring. But they’re not. They’re melting..."

https://climate.nasa.gov/blog/2578/a-vast-melting-desert/

Good read.