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Author Topic: EAIS Contributions to SLR by 2100  (Read 74148 times)


AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #151 on: December 16, 2016, 09:30:43 PM »
observations re Totten glacier

For those of you who hesitate to click on links, I provide the following information; which helps to quantify the extent of recent ocean-ice interaction with the Totten Ice Shelf.

Stephen Rich Rintoul, Alessandro Silvano,  Beatriz Pena-Molino,  Esmee van Wijk,  Mark Rosenberg,  Jamin Stevens Greenbaum and Donald D. Blankenship (16 Dec 2016), "Ocean heat drives rapid basal melt of the Totten Ice Shelf", Science Advances, Vol. 2, no. 12, e1601610, DOI: 10.1126/sciadv.1601610

http://advances.sciencemag.org/content/2/12/e1601610

Abstract: "Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s−1 of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level."
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georged

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Re: EAIS Contributions to SLR by 2100
« Reply #152 on: December 17, 2016, 12:18:43 PM »

Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s−1 of warm water enters the cavity through a newly discovered deep channel.

If my math is right, that's 220,000 cumec/s. Which is equivalent to 1000 of this: http://www.greatlaketaupo.com/things-to-do/must-do/huka-falls/

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #153 on: December 17, 2016, 04:38:55 PM »
The linked article is entitled: "East Antarctica is Melting From Above and Below".

http://www.climatecentral.org/news/east-antarctica-melting-climate-change-20986

Extract: "East Antarctica is remote even by Antarctic standards. Harsh winds and ocean currents have largely cut off the region from the rest of the world.

That’s left its massive stores of ice largely intact, especially compared to West Antarctica where a massive meltdown is underway that could raise seas by 10 or more feet in the coming centuries. But as carbon pollution warms the air and the ocean, there are signs that the region’s stability is under threat. Two new studies of different ice shelves — tongues of ice that essentially act as bathtub plugs — have seen major melting that could portend a less stable future for the region."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #154 on: January 03, 2017, 06:28:08 PM »

The linked reference is entitled: "Validation of satellite altimetry by kinematic GNSS in central East Antarctica", and it discusses how radar altimetry was used to improve the accuracy of ice-surface elevations in the central East Antarctica area.

Schröder, L., Richter, A., Fedorov, D. V., Eberlein, L., Brovkov, E. V., Popov, S. V., Knöfel, C., Horwath, M., Dietrich, R., Matveev, A. Y., Scheinert, M., and Lukin, V.: Validation of satellite altimetry by kinematic GNSS in central East Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-282, in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2016-282/

Abstract. Ice-surface elevation profiles of more than 30.000 km in total length are derived from kinematic GNSS observations on sledge convoy vehicles along traverses between Vostok station and the East Antarctic coast. The profiles have accuracies between 4 and 9 cm. They are used to validate elevation datasets from both radar and laser satellite altimetry as well as four digital elevation models. A crossover analysis with three different Envisat radar altimetry datasets yields a clear preference for the relocation method over the direct method of slope correction and for threshold retrackers over functional fit algorithms. The validation of Cryosat-2 low-resolution mode and SARIn mode datasets documents the progress made from baseline B to C elevation products. ICESat laser altimetry data are demonstrated to be accurate to a few decimeters over wide range of surface slopes. A crossover adjustment above subglacial Lake Vostok combining ICESat elevation data with our GNSS profiles yields a new set of ICESat laser campaign biases and provides new, independent evidence for the stability of the ice-surface elevation above the lake. The evaluation of digital elevation models reveals the importance of radar altimetry for the reduction of interpolation errors.
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AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #155 on: January 16, 2017, 06:11:38 PM »
The linked article is entitled: "Epic Antarctic voyage maps seafloor to predict ocean rise as glacier the size of California melts".  It will be interesting to eventually read about what the research team finds-out about the long-term melting patterns for Totten.

https://www.theguardian.com/world/2017/jan/15/totten-glacier-antarctic-voyage-to-map-seafloor-hobart-invstigator

Extract: "In East Antarctica, 3,000km south of the West Australian town of Albany, an ice shelf the size of California is melting from below.

The concerning trend was confirmed by Australian scientists in December, who reported that warming ocean temperatures were causing the rapid melt of the end of the Totten glacier, which is holding back enough ice to create a global sea rise of between 3.5 metres and six metres.

On Saturday, a team of international scientists left Hobart aboard the Australian research ship Investigator to map the seafloor ahead of the glacier to trace its history back to the last ice age, in the hopes of predicting its future melting patterns."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

solartim27

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Re: EAIS Contributions to SLR by 2100
« Reply #156 on: January 21, 2017, 05:12:10 AM »
This post got me thinking of Amery, and I found an old Sentinel from Nov 2015 to compare. 
Some calving of the Amery ice shelf in Prydz Bay, near the 'loose tooth'.
Not the best match for the gif, I tried to align the blue masking layer, darker image is 2017.   The big rift change makes me think we may be getting another huge berg floating about soon (it's all relative, 2018 or 19 time frame?).
http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20170115T151915_FB58_S_1.final.jpg (62 MB)

S1A_EW_GRDM_1SSH_20151109T152805_82F0_S_1.final.jpg
FNORD

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #157 on: January 23, 2017, 07:39:44 PM »
The linked reference indicates that East Antarctic ice shelves are more vulnerable than previously thought, with continued anthropogenic global warming:
 
Martin Siegert (2017), "Glaciology: Vulnerable Antarctic ice shelves", Nature Climate Change, Volume: 7, Pages: 11–12, doi:10.1038/nclimate3189

http://www.nature.com/nclimate/journal/v7/n1/full/nclimate3189.html

Summary: "The decay of floating ice shelves around Antarctica speeds up ice flow from the continent and contributes to increased sea-level rise. Now, meltwater attributed to warm winds has been discovered on an East Antarctic ice shelf, suggesting greater vulnerability than previously thought."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #158 on: August 15, 2017, 12:52:06 AM »
The linked article discussed modeling work at UAF that indicates that certain marine glaciers in East Antarctica are less stable than previously thought, and draws particular attention to Totten:

Title: "High-Performance Computing Tracking Earth’s Most Massive Ice Shelves"

https://edgylabs.com/high-performance-computing-ice-shelves/

Extract: "Glaciers are an indispensable climatic indicator for scientists and meteorologists, giving them insight into past climatic events and helping them to make projections in the future.

For over a decade, climatologists at the University of Alaska Fairbanks (UAF) have been working on ice sheet modeling to track ice sheet progress.

UAF created their own open-source Parallel Ice Sheet Model (PISM).

East Antarctica is the world’s largest ice sheet, roughly the size of the U.S. Until recently, the glaciers of East Antarctica, unlike those of the 10-times smaller West Antarctica, were thought to be more stable, because they’re isolated and very cold.

However, a new study by an international group of climatologists suggests otherwise.

It turns out that Totten, the largest glacier in East Antarctica, is melting and retreating at an alarming rate. This glacier alone threatens to raise sea levels."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Daniel B.

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Re: EAIS Contributions to SLR by 2100
« Reply #159 on: August 15, 2017, 03:38:28 PM »
That conclusion stands in contrast from others:

https://www.the-cryosphere-discuss.net/tc-2017-75/tc-2017-75.pdf

"However, the much larger Totten Glacier and the tributaries of the Moscow University Ice Shelf that drain a large fraction of the East Antarctic Ice Sheet show localized areas of ice speed variations but little change in discharge. This result is consistent with recent findings of Li et al. (2016) showing that the Totten Glacier increase in velocity between 2001 and 2007, likely in response to elevated ocean temperature, but has been relatively stable since.

The finding of Li, et. al. can be found here:

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069173/abstract

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #160 on: August 15, 2017, 05:07:26 PM »
The linked reference discusses estimates of representative terrestrial heat flow in central East Antarctica.  Such knowledge is important to help determine the stability of the associated glaciers.  However, such values are not appropriate for use when modeling the stability of large East Antarctic marine glaciers like Totten (which likely has higher rates of geothermal heat flux):

Goodge, J. W.: Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-134, in review, 2017.

https://www.the-cryosphere-discuss.net/tc-2017-134/

Abstract. Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic ice sheets, yet heat flow across Antarctica is poorly known. Previous estimates of terrestrial heat flow come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in ice boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for ice-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East Antarctica coupled to either subglacial sediment or bedrock. Bedrock outcrop is limited to coastal margins and rare inland exposures, yet valuable estimates of heat flow in central East Antarctica can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th and K concentrations in a suite of Proterozoic (1.2–2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East Antarctica indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 μW m-3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33–84 mW m-2 and an average of 48.0 ± 13.6 mW m-2. Estimates of heat production obtained for this suite of glacially-sourced granitoids therefore indicate that the interior of the East Antarctic ice sheet is underlain in part by Proterozoic continental lithosphere with average surface heat flow, providing constraints on both geodynamic history and ice-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central East Antarctica resembles that in the Proterozoic Arunta and Tenant Creek inliers of Australia, but is dissimilar to other areas characterized by anomalously high heat flow in the Central Australian Heat Flow Province. Age variation within the sample suite indicates that central East Antarctic lithosphere is heterogeneous, yet the average heat production and heat flow of four age subgroups cluster around the group mean, indicating minor variation in thermal contribution to the overlying ice sheet from upper crustal heat production. Despite their minor differences, ice-sheet models may favor a geologically realistic model of crustal heat flow represented by such a distribution of ages and geothermal characteristics.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Daniel B.

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Re: EAIS Contributions to SLR by 2100
« Reply #161 on: August 16, 2017, 03:42:54 PM »
We could argue all day about which estimates are most important in determining the stability of the Trotten glacier.  We will not know the answer, until the change in ice mass reveals itself.  This will help in modeling other glaciers on the EAIS.  Trotted is just a small part of the total ice sheet, and may or may not be indicative of the larger.

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #162 on: August 18, 2017, 12:33:05 AM »
Impressive work on the Law glacier by Bader et al.  indicating long term stability at least on that side of the polar plateau. The optimistic headline in the phys.org article overstates the case. An error in the article is publication date, which was apparently in February.

https://phys.org/news/2017-08-validates-east-antarctic-ice-sheet.html

doi:10.1016/j.quascirev.2016.12.005

--
Abstract: Till in an extensive blue ice moraine in the central Transantarctic Mountains at Mt. Achernar shows
relatively continuous deposition by East Antarctic derived ice throughout the last glacial cycle. The most
recently exposed material along the active margin of the Law Glacier (Zone 1) has hummocky topog-
raphy that transitions into to a relatively flat region (Zone 2), followed by a series of ~2 m high
continuous, parallel/sub-parallel ridges and troughs (Zones 3e5). The entire moraine is ice-cored. Past
surface changes of <40 m are indicated by a lateral moraine at the base of Mt. Achernar and substantial
topographic relief across Zone 3.

Pebble lithology and detrital zircon geochronology were analyzed on samples along a 6.5 km transect
across the moraine which formed from sub- and englacial debris. Beacon and Ferrar Supergroup rocks
comprise most rock types on the moraine surface. Overall, pebbles in Zones 1, 4 and 5 are dominated by
igneous rocks of the Ferrar dolerite, whereas Zones 2 and 3 have ~40% more Beacon Supergroup sedi-
mentary rocks. Zone 4 is characterized by distinctly colored lithologic bands, 5e20 m wide, that alternate
between dominant Beacon and Ferrar rock types. When combined with surface exposure ages, we
conclude that Zones 2 and 3 contain sediment accumulated through the last glacial maximum (LGM). In
contrast to pebble data, the U-Pb zircon data from till across all zones show little variability and are
consistent with a Beacon Supergroup source, as samples show significant populations from the Prote-
rozoic, ~550-600 Ma and ~950-1270 Ma, as well as the late Archean ~2700-2770 Ma. The Mackellar,
Fairchild, and lower Buckley Formations are interpreted as dominant sources of the detrital zircons. The
zircon data lack the spatio-temporal variability indicated by the pebble fraction because the local Ferrar dolerite is not zircon bearing, highlighting the broader importance of using multiple techniques when interpreting provenance changes over time.

Rather than reflecting major changes in ice flow path over time, the provenance changes are inter-
preted to indicate relative stability of the East Antarctic ice sheet, as the Law Glacier tapped into and
eroded successively lower stratigraphic units of the Beacon Supergroup. This has important implications
for interpreting offshore provenance records.
--

Very nice. Unfortunately paywalled. I attach figs 3b,c and part of 9 to give a flavor. They conclude:

" ... that is, provenance changes can be explained solely by Law Glacier tapping into successively lower stratigraphic units of the Beacon Supergroup, rather than indicating significant changes within East Antarctic ice sheet catchment boundaries. This has important implications for interpreting long temporal record from cores, such as ANDRILL. For instance, provenance analysis of a core collected downstream of an outlet glacier, such as the Law/Lennox-King Glacier system ... "

sidd