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Author Topic: EAIS Contributions to SLR by 2100  (Read 80782 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.”
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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.”
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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.”
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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


AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #163 on: November 01, 2017, 08:49:28 PM »
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."
“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 #164 on: November 02, 2017, 09:40:29 PM »
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

In other words, they don’t know.

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."

AbruptSLR

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Re: EAIS Contributions to SLR by 2100
« Reply #165 on: November 03, 2017, 10:16:13 PM »
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

In other words, they don’t know.

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."

While scientists many not know everything about projecting future impacts of climate change on the Totten Glacier and Ice Shelf, your post indicates that you know even less.
“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 #166 on: November 04, 2017, 02:53:04 PM »
The linked reference concludes: "Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."  This is not good news:

Chad A. Greene, Donald D. Blankenship, David E. Gwyther, Alessandro Silvano and
Esmee van Wijk (01 Nov 2017), "Wind causes Totten Ice Shelf melt and acceleration",
Science Advances, Vol. 3, no. 11, e1701681, DOI: 10.1126/sciadv.1701681

http://advances.sciencemag.org/content/3/11/e1701681

In other words, they don’t know.

Abstract: "Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."

While scientists many not know everything about projecting future impacts of climate change on the Totten Glacier and Ice Shelf, your post indicates that you know even less.

And this coming from the person who just parrots others opinions!  Perhaps if you took the time to listen to those with whom you disagree, you may learn something.  “There is none so blind as he you will not see.”

Shared Humanity

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Re: EAIS Contributions to SLR by 2100
« Reply #167 on: November 04, 2017, 04:16:52 PM »


While scientists many not know everything about projecting future impacts of climate change on the Totten Glacier and Ice Shelf, your post indicates that you know even less.

ASLR....

I've not bothered to read Daniel B's response to this comment as I have him on ignore. He is a troll and a not very bright one at that. I consider you one of this site's top resident experts, a source of links to research that can help any visitor gain an appreciation of the challenges we face with regards to climate change. Responding to this clown is a waste of your time.

Shared Humanity

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Re: EAIS Contributions to SLR by 2100
« Reply #168 on: November 04, 2017, 06:52:52 PM »
Oh....and please keep on doing the work that you do.

oren

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Re: EAIS Contributions to SLR by 2100
« Reply #169 on: November 05, 2017, 12:32:32 AM »
Daniel B., I just have had enough with you. I've seen some posts from you that I disliked as they all seemed biased in one direction and sometimes derailing the discussions. But I did give you the benefit of the doubt until today. Quotingthe whole post by ASLR, one of the most respected posters on the site, just to stick an unexplained slur in the middle, and then when rebuked you resort to an ad hominem attack, there can be no other verdict but that you are an intentional troll. Best begone.

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #170 on: November 05, 2017, 02:14:56 AM »
Perhaps use a killfile, rather than posting insults ? And perhaps we discuss the paper forawhile ?

Recall that the antarctic circumpolar wind drives the antarctic circumpolar current toward the east in deep ocean, while over the continental shelf further south a westward wind drives the Antarctic coastal current from east toward the west. This result is surprising in that westward wind stress over the shelf would naively, from Ekman pumping arguments, be supposed to depress thermocline and circumpolar deep water exchange, and hence ice melt beneath Totten. They find that when you look closely at local wind patterns that may not be the case.

"Over the continental shelf, westward winds are expected to induce southward transport of surface water, depress isotherms, and could therefore prevent mCDW from surmounting the continental shelf (28, 29), yet we provide evidence that competing processes prevail."

They use ice shelf velocity (from MOSDIS) as a proxy for bottom melt and ERA interim reanalysis for wind. They calculate upwelling due to Ekman pumping from the surface wind velocity.  They use data from February 2001 to September 2014. They find the the Totten ice shelf accelerates 19 months after upwelling increases in certain areas around the mouth of Totten.

What of the future ? Models indicate that the Antarctic Circumpolar winds and antarctic coastal currents eastward strengthen. But the effect on westward coastal winds and coastal current is not clear.

"Projections show an intensification of the wind-driven Antarctic Circumpolar Current and an increase in upwelling, particularly along the East Antarctic continental slope (36, 38, 39). It is possible that westward winds along the coast could weaken in conjunction with a southward migration of the divergence zone (39), in which case mCDW delivery to TIS could be tempered by a weakened coastal current; however, projections of coastal westward winds near TIS are few, and their relationships to SAM or atmospheric greenhouse gas have not been validated."

They continue:

"Wind patterns over the Southern Ocean are expected to evolve throughout the 21st century, and a shifting regime of upwelling could precipitate a marked response in Totten Glacier, unlocking the door to at least 3.5 m of eustatic sealevel potential (13) in the vast ice basin it drains."

But it not clear exactly what those shifting regimes of upwelling will be, since there are no climate models yet that have the skill or resolution for local regions around Totten over small timescales. So I think the last sentence of the abstract is too strong.

"Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations."

They should have stopped after the comma, since it is not clearly projected that surface coastal winds will increase. All that is projected clearly is that the Antarctic circumpolar winds and current will increase.

I think this is an ingenious paper, and I don't have major quibbles with linking ice shelf velocity to bottom melt, but i think that the calculation from surface wind stress to upwelling is not so well supported and must await longer time series measurements of ocean upwelling over a larger area. (They do have float data from a single float for 2015 and have shown some correlation but that is just for that year along that float track using the -0.4C isotherm depth as as proxy for upwelling.)  Projections for the future must likewise await models with finer temporal and spatial resolution and accuracy. That said, I dont see how the strengthened ACC in the deep ocean forcing more CDW upward wont find a way to the bottom of Totten and the rest, but that's just me.

sidd
« Last Edit: November 05, 2017, 08:02:55 AM by sidd »

Daniel B.

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Re: EAIS Contributions to SLR by 2100
« Reply #171 on: November 05, 2017, 02:42:45 AM »
Daniel B., I just have had enough with you. I've seen some posts from you that I disliked as they all seemed biased in one direction and sometimes derailing the discussions. But I did give you the benefit of the doubt until today. Quotingthe whole post by ASLR, one of the most respected posters on the site, just to stick an unexplained slur in the middle, and then when rebuked you resort to an ad hominem attack, there can be no other verdict but that you are an intentional troll. Best begone.

Funny how you ignored Abrupts slur and as hominem, but took offense when I responded back.  I guess it just goes to show your own bias.  Perhaps you are the troll.

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Re: EAIS Contributions to SLR by 2100
« Reply #172 on: November 05, 2017, 02:56:30 AM »
Sidd,
That was precisely the issue that I had with this paper.  Too much conjecture, based on uncertainty.  Logically, it makes sense that greater upwelling will negatively affect the stability of the Trotten.  However, they seemed to lack any hard data to support their conclusions.

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Re: EAIS Contributions to SLR by 2100
« Reply #173 on: November 05, 2017, 03:23:27 AM »
Projections for the future must likewise await models with finer temporal and spatial resolution and accuracy. That said, I dont see how the strengthened ACC in the deep ocean forcing more CDW upward wont find a way to the bottom of Totten and the rest, but that's just me.

sidd

sidd,

So long as scientific papers cite all of their assumptions and limitations, they do not need to await the development of better models before presenting their results; otherwise, science will not make much progress.  The reason for publishing uncertain results is both to help guide future models and to provide some degree of warning before Totten reaches a tipping point where global warming will not matter, but the marine glacier will be lost due gravity.

That said, of course more data and better models are a good idea, but an even better idea would be to stop anthropogenic radiative forcing and then to take atmospheric CO2 concentrations back to 350ppm per James Hansen's advice.

Best,
ASLR
« Last Edit: November 05, 2017, 03:42:43 AM by AbruptSLR »
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Re: EAIS Contributions to SLR by 2100
« Reply #174 on: November 05, 2017, 03:46:27 AM »
The linked SciAm article provides some more insights into the Greene et al (2017) paper:

Title: "How Wind Might Nudge a Sleeping Giant in Antarctica"

https://www.scientificamerican.com/article/how-wind-might-nudge-a-sleeping-giant-in-antarctica/

Extract: "Climate projections suggest that the upwelling of warm water may increase over the next century, Greene noted.

"Upwelling is driven not purely by the broad-scale magnitude of wind, but by the gradient in wind—how strong the wind is at one latitude versus how strong it is at a different latitude," he explained. "And CO2 in the atmosphere is modeled to increase the wind gradient around Antarctica, and then therefore increase upwelling around Antarctica."

What that actually means for the future of the sleeping giant is unclear for now. How the flow of ice could change in real time is closely tied to the region's underwater topography, which affects how quickly the glacier retreats as the ice shelf melts. These are issues scientists are still investigating.

"In all reality, Totten isn't going to destabilize in our lifetimes and then dump that 11 feet of sea-level rise into the ocean," Greene said. In fact, the increasingly unstable glaciers of West Antarctica remain a far bigger near-term concern among scientists for now."
« Last Edit: November 05, 2017, 09:37:50 AM by AbruptSLR »
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Re: EAIS Contributions to SLR by 2100
« Reply #175 on: November 05, 2017, 07:52:31 AM »
...
I think this is an ingenious paper, and I don't have major quibbles with linking ice shelf velocity to bottom melt, but i think that the calculation from surface wind stress to upwelling is not so well supported and must await longer time series measurements of ocean upwelling over a larger area. (They do have float data from a single float for 2015 and have shown some correlation but that is just for that year along that float track using the -0.4C isotherm depth as as proxy for upwelling.)  Projections for the future must likewise await models with finer temporal and spatial resolution and accuracy. That said, I dont see how the strengthened ACC in the deep ocean forcing more CDW upward wont find a way to the bottom of Totten and the rest, but that's just me.

sidd
Thank you sidd for the well-explained criticism of the paper.

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Re: EAIS Contributions to SLR by 2100
« Reply #176 on: November 05, 2017, 09:43:23 AM »
Sidd,
That was precisely the issue that I had with this paper.  Too much conjecture, based on uncertainty.  Logically, it makes sense that greater upwelling will negatively affect the stability of the Trotten.  However, they seemed to lack any hard data to support their conclusions.

The linked reference provides direct evidence that ocean currents are currently driving rapid basal ice melt for 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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Re: EAIS Contributions to SLR by 2100
« Reply #177 on: November 05, 2017, 04:46:43 PM »
There you go....quoting him so I have to read his comment.

Thanks for the link to research indicating a mechanism exists at Totten that has been found to operate at most, if not all, marine terminating glaciers.

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Re: EAIS Contributions to SLR by 2100
« Reply #178 on: November 05, 2017, 08:08:31 PM »
Abrupt SLR, as a long time lurker who reads most of your posts, I think it is a good time to thank you for your contribution to this Forum.  Yes, we do not understand all the details about Totten Glacier, however there are some pretty good indications of where it is headed.  Please ignore the troll(s) and continue your informative posts.

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Re: EAIS Contributions to SLR by 2100
« Reply #179 on: November 06, 2017, 01:23:30 AM »
Abrupt SLR, as a long time lurker who reads most of your posts, I think it is a good time to thank you for your contribution to this Forum.  Yes, we do not understand all the details about Totten Glacier, however there are some pretty good indications of where it is headed.  Please ignore the troll(s) and continue your informative posts.

Thank you.  Maybe a good many of my posts primarily present new climate change data (including projections from imperfect models), but to paraphrase a great author, it is not possible to make brick without clay.
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Re: EAIS Contributions to SLR by 2100
« Reply #180 on: November 06, 2017, 10:45:09 PM »
... multi-meter sea level rise this Century is not out of the question

https://robertscribbler.com/2017/11/06/sleeping-ice-giants-stir-east-antarcticas-totten-glacier-accelerates-toward-southern-ocean/#comment-128987

Sleeping Ice Giants Stir — East Antarctica’s Totten Glacier Accelerates Toward Southern Ocean
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

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Re: EAIS Contributions to SLR by 2100
« Reply #181 on: November 07, 2017, 05:10:56 PM »

Sleeping Ice Giants Stir — East Antarctica’s Totten Glacier Accelerates Toward Southern Ocean


wili,

Thanks for the link to the Scribbler article on Totten.  I post two images from that article (the first showing the general area of Totten and the second showing the upwelling zone in 2002 which fluctuates with the winds), in order to provide context for my repost of the third image that shows the location of an un-named gyre offshore of Totten that clearly interacts with the upwelling zone.  Specifically, such gyre can entrain CDW and advect it into the upwelling zone that lifts the relatively warm CDW up onto the continental shelf where it can be guided to the grounding line for Totten based on bottom bathymetry.

Best,
ASLR
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Re: EAIS Contributions to SLR by 2100
« Reply #182 on: December 13, 2017, 10:33:15 PM »
Marine glaciers in the Aurora subglacial basin are less stable than consensus science previously thought:

Gulick et al. (2017), "Initiation and long-term instability of the East Antarctic Ice Sheet", Nature, nature.com/articles/doi:10.1038/nature25026

http://www.nature.com/articles/nature25026

Abstract: "Antarctica’s continental-scale ice sheets have evolved over the past 50 million years. However, the dearth of ice-proximal geological records limits our understanding of past East Antarctic Ice Sheet (EAIS) behaviour and thus our ability to evaluate its response to ongoing environmental change. The EAIS is marine-terminating and grounded below sea level within the Aurora subglacial basin, indicating that this catchment, which drains ice to the Sabrina Coast, may be sensitive to climate perturbations. Here we show, using marine geological and geophysical data from the continental shelf seaward of the Aurora subglacial basin, that marine-terminating glaciers existed at the Sabrina Coast by the early to middle Eocene epoch. This finding implies the existence of substantial ice volume in the Aurora subglacial basin before continental-scale ice sheets were established about 34 million years ago. Subsequently, ice advanced across and retreated from the Sabrina Coast continental shelf at least 11 times during the Oligocene and Miocene epochs. Tunnel valleys associated with half of these glaciations indicate that a surface-meltwater-rich sub-polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming. Cooling since the late Miocene resulted in an expanded polar EAIS and a limited glacial response to Pliocene warmth in the Aurora subglacial basin catchment. Geological records from the Sabrina Coast shelf indicate that, in addition to ocean temperature, atmospheric temperature and surface-derived meltwater influenced East Antarctic ice mass balance under warmer-than-present climate conditions. Our results imply a dynamic EAIS response with continued anthropogenic warming and suggest that the EAIS contribution to future global sea-level projections may be under-estimated."

See also:

Title: "East Antarctic Ice Sheet has history of instability"

https://phys.org/news/2017-12-east-antarctic-ice-sheet-history.html

Extract: "The new results came from geophysical and geological data collected during the first-ever oceanographic survey of East Antarctica's Sabrina Coast. The glaciers in this region may be particularly susceptible to climate change because they flow from the Aurora Basin, a region of East Antarctica that mostly lies below sea level.

Co-lead author Sean Gulick, a research professor at the University of Texas Institute for Geophysics (UTIG) and the UT Department of Geological Sciences (DGS), said the study found that glaciers from the Aurora Basin have been stable only for the past few million years.
"It turns out that for much of the East Antarctic Ice Sheet's history, it was not the commonly perceived large stable ice sheet with only minor changes in size over millions of years," he said. "Rather, we have evidence for a very dynamic ice sheet that grew and shrank significantly between glacial and interglacial periods. There were also often long intervals of open water along the Sabrina Coast, with limited glacial influence.""

&

https://news.nationalgeographic.com/2017/12/east-antarctic-ice-retreat-global-warming/

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sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #183 on: December 14, 2017, 12:35:00 AM »
The last sentence of the Gulick paper reminds me of Mercer's warning about the 0C isotherm.

"Our findings suggest that ice in the ASB catchment may respond dramatically to anthropogenic climate forcing if regional atmospheric warming results in surface meltwater production."

sidd

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Re: EAIS Contributions to SLR by 2100
« Reply #184 on: December 17, 2017, 06:13:15 PM »
Here is more evidence that portions of the East Antarctic marine glaciers near Law Dome are starting to 'wake-up' due to a combination of increasing ocean heat content (in the CDW) and upwelling due to changes in the westerly winds.  I note that once such activity removes the associated 'ice plugs' (that currently guard the Aurora subglacial basin) the rate of ice mass loss will largely depend on the unknown rates for ice cliff failures and hydrofracturing. I also note that one of the images in the linked pdf highlights Agulhas Leakage that is already occurring as the Antarctic ozone hole has already contracted the Antarctic Circumpolar Current southwards:

Catherine C. Walker, Alex S. Gardner & Johan Nilsson (2017 AGU presentation), "The sleeping giant wakes its neighbors? Observations of recent glacier change near Law Dome, East Antarctica in response to a changing ocean"

https://fallmeeting.agu.org/2017/files/2017/12/Melting-Cryosphere-Wednesday-8AM-slides.pdf

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Re: EAIS Contributions to SLR by 2100
« Reply #185 on: December 19, 2017, 04:23:27 AM »
Hmmm.
I have to wonder how many of these tunnels are still uncharted and at what rate inflow might be increasing. That 220,000 cubic meters per second for just one channel discovered, as serious as it sounds may be just be a drop in the bucket compared to totals when you look at that "neighbors" png for example ASLR.
And If this is a self reinforcing feedback where once these currents have bored past the sill ridges into the inland deepening basin, increased exposed ice surface area can increase the velocity both of the incoming denser warm water, and the freshened by melt outgoing surface layer then trouble it surely is. Particularly if as mentioned surface melt becomes common on the top of the ice. If, as we have seen in Greenland the soggy aquifer that persists below the frozen crust of winter then a massive change in the thermal gradient down through the ice sheet is the result. With average surface temperatures annually well below freezing then a stable situation exists with geothermal heat holding the base at melting point and colder temperature as you rise towards the surface. With temps pinned at melting point at the top and bottom, inevitably the whole thickness of the sheet will ease toward melting point, and structural stability of the bottom becomes highly questionable.
Policy: The diversion of NZ aluminum production to build giant space-mirrors to melt the icecaps and destroy the foolish greed-worshiping cities of man. Thereby returning man to the sea, which he should never have left in the first place.
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Re: EAIS Contributions to SLR by 2100
« Reply #186 on: December 20, 2017, 05:00:59 PM »
You will notice that in the attached image from the conservative DeConto & Pollard (2016) analysis, that in panel "c" the "T" stands for Totten Glacier collapsing (due to cliff failures and hydrofracturing) before 2100, with RCP 8.5 radiative forcing:

Caption: "Figure 4 | Future ice-sheet simulations and Antarctic contributions to GMSL from 1950 to 2500 driven by a high-resolution atmospheric model and 1° NCAR CCSM4 ocean temperatures. a, Equivalent CO₂ forcing applied to the simulations, following the RCP emission scenarios in ref. 36, except limited to 8 × PAL (preindustrial atmospheric level, where 1 PAL = 280 p.p.m.v.). b, Antarctic contribution to GMSL. c, Rate of sea-level rise and approximate timing of major retreat and thinning in the Antarctic Peninsula (AP), Amundsen Sea Embayment (ASE) outlet glaciers, AS–BS, Amundsen Sea–Bellingshausen Sea; the Totten (T), Siple Coast (SC) and Weddell Sea (WS) grounding zones, the deep Thwaites Glacier basin (TG), interior WAIS, the Recovery Glacier, and the deep EAIS basins (Wilkes and Aurora). d, Antarctic contribution to GMSL over the next 100 years for RCP8.5 with and without a +3 °C adjustment in ocean model temperatures in the Amundsen and Bellingshausen seas as shown in Extended Data Fig. 5d. e–g, Ice-sheet snapshots at 2500 in the RCP2.6 (e), RCP4.5 (f) and RCP8.5 (g) scenarios. Ice-free land surfaces are shown in brown. h, Close-ups of the Amundsen Sea sector of WAIS in RCP8.5 with bias-corrected ocean model temperatures."
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Re: EAIS Contributions to SLR by 2100
« Reply #187 on: January 30, 2018, 11:34:53 PM »
The linked reference discusses some of the complexities associated with modeling fracture and calving on the Totten Ice Shelf:

Cook, S., Åström, J., Zwinger, T., Galton-Fenzi, B. K., Greenbaum, J. S., and Coleman, R.: 2018, Modelled fracture and calving on the Totten Ice Shelf, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-3

https://www.the-cryosphere-discuss.net/tc-2018-3/

Abstract. The Totten Ice Shelf (IS) has a large drainage basin, much of which is grounded below sea level, leaving the glacier vulnerable to retreat through the Marine Ice Shelf Instability mechanism. The ice shelf has also been shown to be sensitive to changes in calving rate, as a very small retreat of the calving front from its current position is predicted to cause a change in flow at the grounding line. Therefore understanding the processes behind calving on the Totten IS is key to predicting its future sea level rise contribution. Here we use the Helsinki Discrete Element Model (HiDEM) to show that calving on the Totten IS is controlled not only by locally produced fractures at the calving front, but is also influenced by basal fractures which are likely produced at the grounding line. Our model results show that regrounding points may be key areas of basal crevasse production, and can produce basal crevasses in both an along and across flow orientation. As well as affecting calving, along flow basal crevasses at the grounding line may be a possible precursor to basal channels. We use two additional models to examine the evolution of basal fractures as they advect downstream, demonstrating that both strain and ocean melt have the potential to deform narrow fractures into the broad basal features observed near the calving front. The wide range of factors which influence fracture patterns and calving on this glacier will be a challenge for predicting its future mass loss.
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