Antarctic Tectonics

[AbruptSLR]

Most of what I have posted focuses on ice and the risk of ice mass loss contributing to abrupt sea level rise, ASLR; however, some of my posts have made it clear that any significant loss of ice mass will engage the underlying continental crust/upper mantle (lithosphere/asthenosphere); for reasons including: Glacial Isostatic Adjustment (GIA); volcanism; seismicity; rift valleys; and bed characteristics.  Therefore, I have opened this new thread to briefly examine selected aspects of the relatively unique/peculiar Antarctic tectonics/geology.

To begin this thread I start with some aspects of the Gondwana breakup, with the attached four images coming from Sears 2006:

The first image shows the southern supercontinent Gondwana about 183million year ago at the point of the initial breakup of the supercontinent.

The second image highlights the Euler geometry of hexagons and pentagons bounded by the supercontinent rupture lines that define the lines of minimum energy required to break apart the supercontinent.

The third image shows the correspondence of tectonic hotspots from the time of breakup to the modern geometry.

The fourth image shows the direction of migration of other tectonic plates from Antarctica, together with the modern seafloor, plate margins and historical hotspot locations.

[AbruptSLR]

The post is intended to provide more generic background on Antarctic tectonics, with the first two images in this post coming from:

http://www.largeigneousprovinces.org/apr13

The links between large igneous provinces, and continental break-up: evidence reviewed from Antarctica
by: Bryan C Storey,  Alan P M Vaughan and Teal R Riley; April 2013
Gateway Antarctica, Private Bag 4800, University of Canterbury, Christchurch, New Zealand; bryan.storey@canterbury.ac.nz

The first attached image shows:  Middle Jurassic Gondwana reconstruction showing three large igneous provinces (after Storey & Kyle 1997); Ferrar, Karoo and Chon Aike, and the location of the Weddell Sea Triple Junction (WSTJ) after Elliot & Fleming 2000.  DML, Dronning Maud Land; FI, Falkland Islands

The second attached image shows:  Antarctic map showing the Transantarctic Mountains as the rift shoulder of the West Antarctic Rift System (WARS), the related Cenozoic alkaline magmatic province (WARS volcanoes), the outline of the Middle Jurassic Ferrar magmatic province and the outline of the mid Cretaceous alkaline magmatism in Marie Byrd Land.

The third attached image shows the modern tectonic plate margins and faults.

[AbruptSLR]

To provide further orientation:

The first attached image shows the Earth's internal structure per the USGS with the  Mohorovicic Discontinuity, shown as a red line.  The Mohorovicic Discontinuity, or "Moho", is the boundary between the crust and the mantle.

The second image shows a map of Antarctica with the relief of the crust thickness below it's ice as indicated by seismic data. Abbreviations: DML, Dronning Maud Land; GSM, Gamburtsev Subglacial Mountains.  CREDIT: Baranov, A., Morelli, A., The Moho depth map of the Antarctica region, Tectonophysics (2013).

The third image focuses on the depth to the MOHO (which can be used to calculate the crust thickness), showing new, more refined, findings. CREDIT: Baranov, A., Morelli, A., The Moho depth map of the Antarctica region, Tectonophysics (2013).  It is important to note that in general the thinner the crust the more geothermal heat is available to melt the base of the overlying ice sheet/glacier.

Findings from the Colorado University at Boulder, CUB, shear velocity model is shown in the fourth image, from:

http://ciei.colorado.edu/~nshapiro/MODEL/

This CUB model uses a large data set of the surface wave fundamental model phase and group velocity measurements, and the findings show the distinct difference between East and West Antarctica.

[AbruptSLR]

Focusing more on the West Antarctic:

The first image provides a schematic of the West Antarctic Rift and its relationship to the Transantarctic Mountains.

The second image provides an overview of the West Antarctic Rift System, WARS.
The third and fourth images and summary in this post are from:

"Tectonic implications for uplift of the Transantarctic Mountains
By: J. F. Lawrence, J. W. van Wijk, and N. W. Driscoll

U.S. Geological Survey and The National Academies; USGS OFR-2007-xxxx, Extended Abstract.yyy, 1-4

A pdf of this paper can be found at:

http://www.lanl.gov/orgs/ees/ees11/geophysics/staff/vanwijk/Jolante_1.pdf

 Summary The Transantarctic Mountains are a non-compressional mountain belt located on the tectonic boundary between cratonic East Antarctica and non-cratonic West Antarctica. Formation of this mountain belt and a possible relation with the West Antarctic Rift system are still debated. Here we suggest a new explanation for uplift of the mountains, formation of a small crustal root, depression of the hinterland Wilkes Basin and formation of the West Antarctic Rift system. Using thermo-mechanical models to study deformation of the tectonic boundary, we find that convergence of crustal material at the craton edge during extension results in formation of a small crustal root and uplift of the surface. Crustal material accumulates at the craton edge during extension because the cratonic lithosphere is too strong to deform. This explains the location of the mountains. We further suggest that the West Antarctic Rift system formed at the side of the craton because this is the weakest location in the region. The hinterland Wilkes Subglacial Basin is a flexural depression; thermo-mechanical models show that rifting does not occur in the hinterland as the craton is simply too strong. Our models thus suggest that uplift of the Transantarctic Mountains is related to formation of the West Antarctic Rift system and flexural depression of the Wilkes Basin."

The caption for third attached image is: Subglacial topography and bathymetry map of Antarctica (Lytte et al., 2000). The black dotted lines are the inferred boundary of the West Antarctic Rift System from Rocchi et al. (2002). Right panels show the lithosphere structure prior to the extensional phase used in the thermo-mechanical model, with the cold craton of East Antartcia and warmer non-cratonic lithosphere of West Antarctica.

The fourth image shows the modeled internal structure of the lithosphere in West Antarctica, showing a major source of heat from the upper mantle.

[AbruptSLR]

As discussed in the WAIS Divide Core thread, Mt. Erebus has played a key role in the WAIS past and if it is activated again (possibly by the loss of sufficient WAIS ice mass) it could play an important part in the WAIS's future.

From the following summary and image are from:

 http://erebus.nmt.edu/index.php/volcanology/51-volcanological-evolution

"Prior to the early 1990's, much was known about the geochemical evolution of lavas from Mt. Erebus. Clearly, the stratigraphically oldest lavas were of a primitive basanitic composition, while the current activity is a more chemically evolved tephriphonolite. However, only a few age dates existed for the whole of Mt. Erebus and these were limited to imprecise conventional K/Ar dates. Beginning in 1993, Dr. Philip Kyle and two of his students (Chris Harpel and Richard Esser) began utilizing the more advanced, high precision 40Ar/39Ar dating technique to determine the ages of many of the exposed lava flows on Mt. Erebus. Prior to the use of 40Ar/39Ar geochronology on Mt. Erebus, what little age data existed suggested that the volcano was several million years old, including the young-looking summit area. We now know that the entire volcano is just slightly older than 1 million years old and that the summit is significantly younger than 100,000 years old.

By combining the new geochronologic data with the existing database of geochemical data, we can better confirm an evolutionary model for the development of Mt. Erebus. Below are the summarized results from several researchers working on the evolution of the volcano.

Mt. Erebus is one of several volcanoes in the McMurdo Volcanic Group which itself consists of Late Cenozoic intraplate alkaline volcanoes."

The caption for the attached figure is:  Cross-section of the crust and upper mantle below Ross Island, Antarctica. A "hot spot" or mantle plume is theorized as the mechanism to account for the origin of Mt. Erebus and Ross Island

[ggelsrinc]

I've been looking for a volcanic/ice sheet connection for years, because many things hinted at it, but the evidence was hidden below the ice sheets. Fortunately, we live during a time when some of those ice sheets have melted away.

Unusual patterns in the lava also point to eruptions under, over and alongside glaciers, which could help scientists pinpoint the size of Alaska's mountain glaciers during past climate swings.

While the volcanoes in Canada and Alaska have erupted for more than 10 million years, emerging data suggests that the last 3 million years of glaciers growing and retreating in Alaska and British Columbia also prompted many small volcanoes to erupt, because the changing ice mass flexed the Earth. This activated the fractures and made room for more magma to rise.

East of Ketchikan, a basalt flow lapped onto a 42,000-year-old beach, preserving shells, pinecones, pine needles and pollen. Barnacle plates sitting on top of the lava are about 13,000 years old, Baichtal said. The whole package now sits about 260 feet (80 meters) above sea level, hinting at how much Earth's crust has bobbed up since the last ice age.

Source: http://science.nbcnews.com/_news/2013/06/03/18726557-12-new-volcanoes-found-in-southeast-alaska?lite

Sea level rise since 13,000 years ago is about 80 meters, but those barnacles on top of the lava are now 80 meters above sea level, which means isostatic rebound was about 160 meters since they lived in the sea. That Northern Cordilleran Volcanic Province mentioned in the article is a good distance from a subduction zone and covers a large area. The picture I've been given of glaciers that terminate on ice shelfs is they can lose the ice shelfs and anchor, speed up quickly losing mass, but eventually slow down as friction and the slope changes. I thought about assistance from isostatic rebound, but figured it was too slow. That article made me wonder could the isostatic rebound get additional assistance from volcanism (whether volcanos or hot springs) to melt glaciers and ice sheets faster than the pure mechanical model with additional positive feedbacks, like ash?

Your sketch of a volcano near an ice sheet around a subduction zone and interest in ASLR reminded me of that article and I know WAIS was also involved in the Eemian SLR. I think I'll look around for volcanic and hot spring associations with other ice sheets that have melted away. I'm particularly interested if a nearby subduction zone is a requirement. That Mt Erebus sketch looks to put the active area from a subduction zone towards EAIS. Areas on Earth experiencing ice sheets should have had many periods of flex producing fractures below as ice sheets came and went. Antarctica changed many times since glaciation started. The Northern Cordilleran Volcanic Province was well glaciated with ice sheets not so long ago, it wasn't just mountain glaciers like today, so the first quote is misleading. 

[AbruptSLR]

ggelsrinc,

Thanks for the background on Alaskan volcanic activity.  I would like to pointout that while the basics are the same, the particulars of the West Antarctic are different than many other areas of the world for reasons including:
- The crust is very thin in many parts of the West Antarctic which allows more geothermal heat to help melt the bottoms of the ice sheets faster than in many other places.
- The tongue of asthenosphere penetrating up through the lower lithosphere means that the magama, ash and gas emissions in the West Antarctic Rift System, WARS, are typically different than in other parts of the world (eg a lack of sufate emission means less cooling and more warming associated with eruptions).
- The apparent subduction zone is different that in other parts of the world because of the thick East Antarctic crust.
- The rate of glacial isostatic adjustment (rebound) is much higher in the Byrd Subglacial Basin than in most any other part of the world, implying that more warm asthenosphere material is welling up as ice mass loss occurs in this ice sheet drainage basin, which will increase the geothermal basal melting, promote more volcanism, and more earthquakes.

I agree that researchers should consider all of these consideration in the RCM and LCM projections for ice mass loss; but I will not that the WARS is potentially considerably more impactive on ice mass loss than would be the typical case for volcanism in other parts of the world.  Therefore, we should look to places like Alaska to learn, but RCM and LCM models of WAIS but be calibrated for the local conditions (and not for other less severe conditions).

Best,
ASLR

[AbruptSLR]

The following summary and attached image are from:

Inland thinning of West Antarctic Ice Sheet steered along subglacial rifts
Robert G. Bingham, Fausto Ferraccioli, Edward C. King, Robert D. Larter, Hamish D. Pritchard, Andrew M. Smith & David G. Vaughan
Nature, Volume: 487, pp 468–471, 26 July 2012; doi:10.1038/nature11292

"Current ice loss from the West Antarctic Ice Sheet (WAIS) accounts for about ten per cent of observed global sea-level rise1. Losses are dominated by dynamic thinning, in which forcings by oceanic or atmospheric perturbations to the ice margin lead to an accelerated thinning of ice along the coastline. Although central to improving projections of future ice-sheet contributions to global sea-level rise, the incorporation of dynamic thinning into models has been restricted by lack of knowledge of basal topography and subglacial geology so that the rate and ultimate extent of potential WAIS retreat remains difficult to quantify. Here we report the discovery of a subglacial basin under Ferrigno Ice Stream up to 1.5 kilometres deep that connects the ice-sheet interior to the Bellingshausen Sea margin, and whose existence profoundly affects ice loss. We use a suite of ice-penetrating radar, magnetic and gravity measurements to propose a rift origin for the basin in association with the wider development of the West Antarctic rift system. The Ferrigno rift, overdeepened by glacial erosion, is a conduit which fed a major palaeo-ice stream on the adjacent continental shelf during glacial maxima. The palaeo-ice stream, in turn, eroded the ‘Belgica’ trough, which today routes warm open-ocean water back to the ice front to reinforce dynamic thinning. We show that dynamic thinning from both the Bellingshausen and Amundsen Sea region is being steered back to the ice-sheet interior along rift basins. We conclude that rift basins that cut across the WAIS margin can rapidly transmit coastally perturbed change inland, thereby promoting ice-sheet instability."

The attached image indicates that the Ferrigno rift (formed due to West Antarctic Tectonics) accommodates the Ferringo Ice Stream; which could retreat due to ocean warming, which in turn would direct warm CDW into the heart of the WAIS.

[AbruptSLR]

The following quote, and three attached images, regarding Post Glacial Rebound, PGR (or Glacial Isostatic Adjustment, GIA) are from:

http://grace.jpl.nasa.gov/data/pgr/

A, G., J. Wahr, and S. Zhong (2013) "Computations of the viscoelastic response of a 3-D compressible Earth to surface loading: an application to Glacial Isostatic Adjustment in Antarctica and Canada", Geophys. J. Int., 192, 557–572, doi: 10.1093/gji/ggs030

"POST GLACIAL REBOUND DISCUSSION
WHAT IS OFFERED HERE

In order to compute mass trends from GRACE and interpret them as changes in the water content of hydrologic basins, or ocean bottom pressure, or ice sheet mass, one must remove the effect of Glacial Isostatic Adjustment (GIA or PGR) of the lithosphere and mantle.
The GRACE-derived grids described elsewhere in this website have had a reasonable PGR model of secular trends removed, in terms of mass changes expressed as cm of equivalent water thickness per year. Grids of that correction are offered here for users who wish to undo the correction and apply their own PGR model to the GRACE data. By 'popular demand' we also offer grids of the rates of lithospheric uplift and of geoid change with the same PGR model. The model used is that of A, G., J. Wahr, and S. Zhong, 2013. See also Chambers et al, 2010.

WHAT IS POST GLACIAL REBOUND?

Ice ages are periods of long-term reduction in the temperature of Earth's climate, resulting in an expansion of the continental and polar ice sheets and mountain glaciers (see Wikipedia article on ice ages for more details). They are related to but not fully explained by the three Milankovich cycles describing the eccentricity, precession (about the same as the Earth-Sun distance on June 21st), and tilt of the Earth relative to the ecliptic (http://www-istp.gsfc.nasa.gov/stargaze/Sprecess.htm). The most recent global deglaciation event, which marked the end of the most recent 100 kyr ice age cycle of the late Quaternary period began only 21,000 calendar years ago (Peltier, 2004), just before the Milankovitch cycle, and was essentially complete by 6000 years ago, but relative sea level have continued to change, essentially everywhere on the earth's surface, due to this cause. This continuing variation of land and sea levels exists as a consequence of the earth's delayed viscoelastic response to the redistribution of mass on its surface that accompanied deglaciation. In regions that were previously glaciated, such as Canada and Northwestern Europe, relative sea level continues to fall at a rate that is primarily determined by the ongoing post-glacial rebound of the crust and which may exceed 1 cm/yr (in the southeast Hudson Bay region of Canada, this rate is near 1.1 cm/yr). Even at sites that are well removed from the centres of glaciation, however, the rates of relative sea level change that exist as a consequence of ongoing glacial isostatic adjustment are nonnegligible. (e.g., Peltier, 1999).

HOW DOES PGR AFFECT THE EARTH GRAVITATIONAL FIELDS?

The redistribution of lithospheric masses, 'rebounding' from the glacial loading of the last ice age, produces long term ('secular') trends in the Earth's gravity field. These signals literally appear as trends when viewed over 5 to 10 year time periods.

IS PGR AN ERROR IN GRACE DATA?

No, it is not an error, it is a signal of great scientific interest in itself. But if one is studying a hydrologic basin, and wants to know whether or not an apparent trend of decreasing water content measured by GRACE indeed indicates that the basin is drying out, then it is necessary to remove some estimate of the PGR trend. This is precisely what, for example, Velicogna and Wahr (2006) had to do to estimate trends of Antarctica ice loss.

WHICH PGR SOLUTION SHOULD I REMOVE FROM THE DATA?

If you download the data from this site, NO PGR CORRECTION IS NEEDED. We have selected for you a reasonable one, and removed it from the data. We offer the PGR water equivalent grids for those who would like to add back the PGR model in order to substract their preferred model.

WHY ARE THERE THREE TYPES OF PGR GRIDS ?

PGR causes a change in the gravity field, so it can be expressed as a rate of change in the geoid, It can also be expressed as changes in the surface mass distribution that would cause the changes in gravity if the mass were concentrated at the surface, in mm/yr of equivalent water thickness, just as the GRACE grids. . Since PGR causes a physical deformation of the lithosphre, it can be expressed as trends in lithospheric height also in mm/yr. While the units are the same, the physical quantiities they represent is quite different.

IS THIS THE BEST PGR MODEL?

PGR is an area of active research. In fact, GRACE is providing additional constraints to retrieve PGR.
The two main ingredients in any PGR model are
the ice (deglaciation) history
the viscosity profile of the mantle

The A et al (2013) model here has a compressible Earth, and uses the ICE-5G deglaciation history and VM2 viscosity profile, and the same PREM-based elastic structure as Peltier (2004). The model includes polar wander feedback (computed as described in Mitrovica et al, 2005), uses the self-consistent sea level equation to distribute meltwater into the ocean, and includes degree-one terms when computing the uplift rate. (though the degree-one terms are zero for the geoid rate, since the computations are done in a center-of-mass frame). The difference between these results and the previous version presented here (by Paulson et al, 2007, which was available here until Jan 15, 2013), is that (1) these results are compressible, and (2) they use an elastic structure and a viscosity profile that vary continuously with radius throughout the mantle (they use exactly the same radial dependency that Peltier (2004) uses), rather than having them organized into a few homogeneous layers.
As newer versions of the deglaciation history become available, especially for Antarctica, we plan to update these GIA model outputs.

WHAT IS THE UNCERTAINTY IN THIS PGR MODELPGR MODEL?

The uncertainty is about +/- 20%.
The 20% value is somewhat ad-hoc, and comes from looking at results for various viscosity values and alternative deglaciation models for Antarctica and Greenland. This +/-20% probably over-estimates the uncertainty in northern Canada, where the deglaciation history is reasonably well-known; and it probably underestimates the uncertainty in Antarctica and Greenland, where the ice history is not as well-known. Plus, if you happen to be looking at a region where the model is close to zero because it is a transition region from large positive values to large negative values, then +/-20% of near-zero values is likely to underestimate the uncertaint

WHY ARE THERE THREE SMOOTHINGS

The results were smoothed using Gaussian smoothers with the same radii as our ocean and our land GRACE grids, as well as an unfiltered version. The mass estimates are provided on a 1 x 1 degree grid, centered at the half-degree.
The following three figures depict the GIA mass variability in terms of equivalent water thickness, using the 3 filters we offer, two of which are the same as used in our ocean grids and our land grids, respectively, and third one being the unfiltered sum. Images of the effect of GIA in terms of litospheric deformation or
These PGR rates in mm/yr of equivalent water HAVE ALREADY BEEN REMOVED (SUBTRACTED) from mass rates in mm/yr of equivalent water retrieved from GRACE to obtain corrected trends. If you are happy with the specific model described above, you need do nothing. If you prefer to use another model, then you must first add back the PGR model we applied with the same filter."


I would like to highlight the following quote from the above: As newer versions of the deglaciation history become available, especially for Antarctica, we plan to update these GIA model outputs.
This implies that NASA knows that the GIA/PGR corrections applied to the GRACE data may not currently be accountly fully for all of the high rebound being measured in the ASE area.

[AbruptSLR]

I am re-posting the following from the "Surge" thread, reminding all that the GRACE satellite SLR contributions previously reported by NASA are probably 40% too low for at least the ASE area and probably for all of the WAIS due to treating the GIA correction for the WAIS like any other part of the earth when, as I have indicated in my prior posts in this thread, West Antarctica has a relatively unique tectonic history and current condition:


An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica
by: A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich
http://dx.doi.org/10.1016/j.gloplacha.2012.08.001

"Abstract
The present study focuses on the Amundsen Sea sector which is the most dynamical region of the Antarctic Ice Sheet (AIS). Based on basin estimates of mass changes observed by the Gravity Recovery and Climate Experiment (GRACE) and volume changes observed by the Ice, Cloud and Land Elevation Satellite (ICESat), the mean mass change induced by Glacial Isostatic Adjustment (GIA) is derived. This mean GIA-induced mass change is found to be 34.1 ± 11.9 Gt/yr, which is significantly larger than the predictions of current GIA models. We show that the corresponding mean elevation change of 23.3 ± 7.7 mm/yr in the Amundsen Sea sector is in good agreement with the uplift rates obtained from observations at three GPS sites. Utilising ICESat observations, the observed uplift rates were corrected for elastic deformations due to present-day ice-mass changes. Based on the GRACE-derived mass change estimate and the inferred GIA correction, we inferred a present-day ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector. This is equivalent to a global eustatic sea-level rise of 0.27 ± 0.04 mm/yr. Compared to the results relying on GIA model predictions, this corresponds to an increase of the ice-mass loss or sea-level rise, respectively, of about 40%."

[Bruce Steele]

ASLR, I was wondering if the 40% increase in SLR would change any of the predictions you did for the Calif. Ocean Protection Council ? Maybe you could post a link so I could read your report as I will be testifying before a Calif. House select committee on sea level rise next month. They want to hear from a fisherman. I was asked to supply support documents so any suggestions would be helpful. I think they want me to keep it relevant to the fishing industry which makes my job kinda tough. Biological ramifications are difficult to predict but I expect cliff erosion will sand in some nearshore reef structure and natural shorelines will be reduced as SLR comes up against existing infrastructure like roads and rail lines. Additional ideas would be helpful. Sorry if I am off topic , somehow I usually am. 

[AbruptSLR]

Bruce,

First, no I do not think that this 40% increase in GRACE measured SLR contribution from the ASE area ice sheets would have a meaningful impact on my prior assessments at this point in time.  Unfortunately, I cannot post a link to help you with your testimony to the Calif. House select committee on sea level rise (change) next month.  At this time, the best that I can do is to refer you to the old abbreviated list of references that I posted in the "Critique" thread here:

http://forum.arctic-sea-ice.net/index.php/topic,70.0.html

and to slightly augment that list with the following (year old) additional references:

[1]   Alvarez-Solas, J., Robinson, A., and Ritz, C. (2012),  “Can recent ice discharges following the Larsen-B ice-shelf collapse be used to infer the driving mechanisms of millennial-scale variations of the Laurentide ice sheet?”, The Cryosphere, 6, 687–693, 2012, www.the-cryosphere.net/6/687/2012/ doi:10.5194/tc-6-687-2012.
[2]   Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.
[3]   Church, J. A., and White, N.J. (2011), “Sea-Level Rise from the Late 19th to the Early 21st Century.” Surveys in Geophysics, March 2011, doi: 10.1007/s10712-011-9119-1.
[4]   Church, J. A., N. J. White, L. F. Konikow, C. M. Domingues, J. G. Cogley, E. Rignot, J. M. Gregory, M. R. van den Broeke, A. J. Monaghan, and I. Velicogna (2011), Revisiting the Earth's sea-level and energy budgets from 1961 to 2008, Geophys. Res. Lett., 38, L18601, doi: 10.1029/2011GL048794.
[5]   Fretwell, P. et al. (2012), Bedmap2: improved ice bed, surface and thickness datasets for Antarctica", The Cryosphere Discuss., 6, 4305–4361, doi:10.5194/tcd-6-4305-2012.
[6]   Grinsted, A., (2012), "An estimate of global glacier volume", The Cryosphere Discuss., 6, 3647–3666, doi: 10.5194/tcd-6-3647-2012.
[7]   Hanson, S., Nicholls, R., Ranger, N., Hallegatte, S, Corfee-Morlot, J., Herweijer, C. and Chateau, J., "A global ranking of port cities with high exposure to climate extremes", Climatic Change, (2011) 104:89-111, doi: 10.1007/s10584-010-9977-4.
[8]   Hay, C.C., Morrow, E., Kopp, R.E., and Mitrovica, J.X., 2012, "Estimating the sources of global sea level rise with data assimilation techniques", Proceedings of the National Academy of Sciences, April 2012.
[9]   Hiroko Sugioka, Yoshio Fukao and Toshihiko Kanazawa, (2010), "Evidence for infragravity wave-tide resonance in deep oceans" Nature Communications, Volume: 1, number: 84, doi:10.1038/ncomms1083, 05 October 2010.
[10]   Holland, P.R., Corr, H.F.J., Vaughan, D.G., Arthern, R.J., Jenkins, A., and Tedesco, M., (2011), "The air content of Larsen ice shelf", Geophys. Res. Lett., 38, L10503, doi: 10.1029/2011GL047245.
[11]   Javrejeva, S., J.C. Moore and A. Grinsted, (2011), "Sea level projections to AD 2500 with a new generation of climate change scenarios", Global and Planetary Change, 21 September 2011 / doi: 1016/j.gloplacha.2011.09.006
[12]   Kelly, D.L. and Tan, Z., (2011), "Leaning, Growth and Climate Feedbacks" 2011 Camp Resources XVIII, University of Miami, August 15, 2011.
[13]   Khazendar, A., Rignot, E. and Larour, E. (2011), Acceleration and spatial rheology of Larsen C Ice Shelf, Antarctic Peninsula, Geophys. Res. Lett., 38, L09502, doi:10.1029/2011GL046775.
[14]   McGuire, B, (2012), Waking The Giant: How a Changing Climate Triggers Earthquakes, Tsunamis and Volcanoes, Oxford University Press, 320p.
[15]   Radić, V.,  Hock, R., (2011); "Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise", Nature Geoscience, Vol. 4, pp 91-94, doi:10.1038/ngeo1052
[16]   Rignot, E., Mouginot, J., and Scheuchl, B., (2011), "Ice Flow of the Antarctic Ice Sheet" Science, Vol 333, 9 Sept. 2011, pp 1427-1430.
[17]   Rignot, E., I. Velicogna, M. R. van den Broeke, A. Monaghan, and J. Lenaerts (2011), “Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise.” Geophysical Research Letters 38 (5) (March). doi:10.1029/2011GL046583.
[18]   Song, T.Y.; and F. Colberg, (2011), " Deep ocean warming assessed from altimeters, Gravity Recovery and Climate Experiment, in situ measurements, and a non-Boussinesq ocean general circulation model"  Journal of Geophysical Research, VOL. 116, C02020, 16 PP., 2011 doi:10.1029/2010JC006601.
[19]   Stearns, L.A., Smith, B.E., and Hamilton, G.S., (2008), "Increased flow speed on a large East Antarctic outlet glacier caused by subglacial floods", Nature Geoscience 1, 827 - 831, doi:10.1038/ngeo356.
[20]   Thomas, R., Frederick, E., Li, J., Krabill, W., Manizade, S., Paden, J., Sonntag, J., Swift, R., and Yungel, J., (2011), "Accelerating ice loss from the fastest Greenland and Antarctic glaciers," Geophysical Research Letters, Vol. 38, L10502, doi: 10.1029/2011GL047304.
[21]   Vermeer, M., and S. Rahmstorf. (2009a), “Global sea level linked to global temperature.” Proceedings of the National Academy of Sciences 106 (51) (December): 21527-21532. doi:10.1073/pnas.0907765106.
[22]   Vermeer, M. and Rahnstorf, S., (2009b) "Global Sea Level Linked to Global Temperature"

Beyond that many of my post contain more recent references that you may (or may not) wish to add to this list.  Good luck with your testimony!

Best,
ASLR

[AbruptSLR]

Bruce,
To clarify the implications of the GIA one cannot only look at the WAIS but one also needs to look at the EAIS.  This matter is not settled but the following abstract provides additional discussion:

Antarctic Contribution to Sea-level Rise Observed by GRACE with Improved GIA CorrectionBy: Erik R. Ivins, Thomas S. James, John Wahr, Ernst J. O. Schrama, Felix W. Landerer, Karen M. Simon, 2013

"Measurement of continent-wide glacial isostatic adjustment (GIA) is needed to interpret satellite-based trends for the grounded ice mass change of the Antarctic ice sheet (AIS). This is especially true for trends determined from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. Three data sets have matured to the point where they can be used to shrink the range of possible GIA models for Antarctica: the glacial geological record has expanded to include exposure ages using Be; Al measurements that constrain past thickness of the ice sheet, modelled ice core records now better constrain the temporal variation in past rates of snow accumulation, and Global Positioning System (GPS) vertical rate trends from across the continent are now available. The volume changes associated with Antarctic ice loading and unloading during the past 21 thousand years (21 ka) are smaller than previously thought, generating model present-day uplift rates that are consistent with GPS observations. We construct an ice sheet history that is designed to predict maximum volume changes, and in particular, maximum Holocene change. This ice sheet model drives a forward model prediction of GIA gravity signal that in turn, should give maximum GIA response predictions. The apparent surface mass change component of GIA is re-evaluated to be +55 +/- 13 Gt/yr by considering a revised ice history model and a parameter search for vertical motion predictions that best- fit the GPS observations at 18 high-quality stations. Although the GIA model spans a wide range of possible earth rheological structure values, the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity, nor for a preferred lithospheric thickness. GRACE monthly solutions from CSR-RL04 release time series from Jan. 2003 through the beginning of Jan. 2012, uncorrected for GIA, yield an ice mass rate of +2.9 +/- 34 Gt/yr. A new rough upper bound to the GIA correction is about 60-65 Gt/yr. The new correction increases the solved-for ice mass imbalance of Antarctica to -57 +/-34 Gt/yr. The revised GIA correction is smaller than past GRACE estimates by about 50 to 90 Gt/yr. The new upper bound to sea-level rise from AIS mass loss averaged over the time span 2003.0 - 2012.0 is about 0.16 +/- 0.09 mm/yr."

[Bruce Steele]

ASLR, I read and do my best to try and understand the processes driving acidification foremost so that is why I focus so much on ocean currents and water mass formation processes. Global warming, arctic sea ice melt, and all the changes taking place in antartica will change how earth's carbon cycle functions. So for me understanding the processes that are driving the changes  is a very important part in my efforts to explain this subject to other people. Although I have had the pleasure of knowing some very bright and dedicated scientists I don't have the ability to get past pay walls so my education is limited to open access papers and abstracts. When I get really stuck I can ask someone with a degree one or two questions but their time is limited and their loyalty is to their students ,as it should be. I do appreciate all the effort you put into educating people like me . I think there are plenty of people with degrees that could learn a lot from you also but there is a big difference between the support that the academic community gets from each other and someone like me that has ( other than my wife) no backup.     On a personal note I went to commercial dive school when I was 17 and I was making a living as a commercial diver before I could legally buy a beer. I have never had a real job with a boss and the constraints and expectations to conform.  I can pretty much do and say what I please and I have publicly and sometimes rather effectively carried the acidification message.  Politics , walking the hill , agitating , and sometimes annoying my fellow fishermen is a self appointed task. I plan to campaign until the clock runs out, I can be very frank and forceful but this subject is difficult to say the least. I do not enjoy inflicting pain but the whole subject and the consequences for many lifeforms will be painful.    I very much appreciate the effort that you put into educating people who really want to understand how our planet works . Personal somewhat heroic efforts are the order of the day , Neven and everyone on this site deserves kudos.   Enough... Thanks again 

[AbruptSLR]

I thought that I would post the following summary and images from www.antarcticglaciers.org:

"Subglacial volcanoes
by Prof. John Smellie.
In common with other environments, volcanoes also erupt beneath ice sheets and glaciers. Examples are well known from currently and formerly glaciated regions of the world, particularly Iceland, British Columbia and Antarctica. Subglacial volcanoes are distinctive and have been given their own title: “glaciovolcanism”. Glaciovolcanism is defined as “the interactions of magma with ice in all its forms, including snow, firn and any meltwater”. It is a very young science with a history of sporadic research extending back less than a century but interest in the topic has expanded dramatically since about 2000. As well as providing invaluable information on the construction of volcanoes in a uniquely hostile and inaccessible environment, important when predicting the consequences of modern glaciovolcanic eruptions (e.g. Eyjafjallajokull in Iceland, 2010), studies on subglacial volcanoes have also been developed into what is probably now the most powerful methodology for deriving multiple critical parameters of past ice sheets, mainly the Antarctic Ice Sheet.
Subglacial volcanoes as an ice sheet proxy
Studies of past ice sheets using glaciovolcanic outcrops are still in their infancy. They are best developed for examples in Antarctica, where the two largest investigations have now been completed. Because ice is not preserved in the geological record (it melts), it is not intuitively obvious how subglacial volcano sequences can preserve a detailed record of that ice. However, the following information can be derived routinely from glaciovolcanic sequences:
1.   Was ice formerly present?
2.   Ice thickness.
3.   Ice basal thermal regime (see Glacial Processes).
4.   Ice surface elevation.
5.   Ice sheet structure.
These questions are important because answering them will help us understand past ice-sheet responses to environmental change – and this will help us to predict future change better.
Because the volcanic sequences are typically quite thick (hundreds of metres) and contain resistant rocks such as lavas, they are able to persist through multiple overriding events by ice, unlike many much thinner (typically just metres) glacial sediments. However, volcanic eruptions commonly occur at intervals of several tens to hundreds of thousands of years. Thus, the volcanic record is coarse in resolution, comparable with terrestrial glacial sediments but generally worse than in marine sediments.
Glaciovolcanism in Antarctica
Antarctica is the largest glaciovolcanic province in the world. There are many volcanoes and they occur all the way from the sub-Antarctic South Sandwich Islands, through the Antarctic Peninsula and Marie Byrd Land, and into East Antarctica, a distance of about 5000 km. Eruptions coincided with the development of the Antarctic Ice Sheet. The volcanoes are overwhelmingly basaltic and there are few examples of more evolved magmatic compositions [6,7]. They range from very large stratovolcanoes with summit elevations up to 4000 m above sea level and basal diameters of 40 to 60 km, to volcanic fields composed multiple small centres [6,9]. The individual volcanoes are often extremely beautiful but the extensive cover of snow and ice and the remote locations can make accessing them quite challenging

Unlike lower-latitude volcanoes which are typically obscured extensively by vegetation, volcanic outcrops in Antarctica are characteristically very clean and beautifully exposed. In places such as northern Victoria Land, cliff sections up to 2 km high extend 10 or 20 km laterally [8]. However, many volcanoes have minimal exposure or have been extensively removed by multiple overriding ice sheets, particularly in the Antarctic Peninsula. A curiosity of subglacially erupted volcanoes is that, because they are formed of alternating thick sections of lavas and fragmental rocks and are therefore technically stratovolcanoes, the frequent development of lava-fed deltas (see below) has resulted in volcano profiles with slopes less than 15° that are normally associated with (lava-dominated) shield volcanoes. Both terms have been used to describe Antarctic volcanoes."

The first attached image is a cartoon showing a small volcano erupting under an ice sheet, the major rock types formed, meltwater lake and principal meltwater escape routes.

The second attached file shows cartoons illustrating the two generic types of glaciovolcanic sequences that are found in the Antarctic Peninsula. The sequences are very different and were created during eruptions under different ice thicknesses. A. Lava-fed delta sequence. B. Sheet-like sequence.

[AbruptSLR]

In my previous posts about the following research; I did not have current reference citations, which I provide below; and the abstract has changed slightly so I am reposting that abstract; which that the new corrected ice mass balance for Antarctica are now higher than reported before the correction:

Antarctic contribution to sea level rise observed by GRACE with improved GIA correction
By: Erik R. Ivins; Thomas S. James; John Wahr; Ernst J. O. Schrama; Felix W. Landerer; and Karen M. Simon;14 JUNE 2013; Journal of Geophysical Research Solid Earth; DOI: 10.1002/jgrb.50208

Abstract:
"Antarctic volume changes during the past 21 thousand years are smaller than previously thought, and here we construct an ice sheet history that drives a forward model prediction of the glacial isostatic adjustment (GIA) gravity signal. The new model, in turn, should give predictions that are constrained with recent uplift data. The impact of the GIA signal on a Gravity Recovery and Climate Experiment (GRACE) Antarctic mass balance estimate depends on the specific GRACE analysis method used. For the method described in this paper, the GIA contribution to the apparent surface mass change is re-evaluated to be +55±13 Gt/yr by considering a revised ice history model and a parameter search for vertical motion predictions that best fit the GPS observations at 18 high-quality stations. Although the GIA model spans a range of possible Earth rheological structure values, the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity nor for a preferred lithospheric thickness. GRACE monthly solutions from the Center for Space Research Release 04 (CSR-RL04) release time series from January 2003 to the beginning of January 2012, uncorrected for GIA, yield an ice mass rate of +2.9± 29 Gt/yr. The new GIA correction increases the solved-for ice mass imbalance of Antarctica to −57±34 Gt/yr. The revised GIA correction is smaller than past GRACE estimates by about 50 to 90 Gt/yr. The new upper bound to the sea level rise from the Antarctic ice sheet, averaged over the time span 2003.0–2012.0, is about 0.16±0.09 mm/yr."

[AbruptSLR]

The following paper finds that ice mass loss estimates for GRACE observations for the Antarctic are highly dependent upon the GIA correction used (which the authors state to be uncertain).  That said the latest GIA data makes me believe the −147 ± 80 Gt/yr average ice mass loss for AIS from 2003 thru 2012, cited below:

Time-variable gravity observations of ice sheet mass balance: Precision and limitations of the GRACE satellite data
by: I. Velicogna, and J. Wahr; Article first published online: 27 JUN 2013; Geophysical Research Letters, DOI: 10.1002/grl.50527

Abstract:
"Time-variable gravity data from the Gravity Recovery and Climate Experiment (GRACE) mission have been available since 2002 to estimate the mass balance of the Greenland and Antarctic Ice Sheets. We analyze current progress and uncertainties in GRACE estimates of ice sheet mass balance. We discuss the impacts of errors associated with spherical harmonic truncation, spatial averaging, temporal sampling, and leakage from other time-dependent signals (e.g., glacial isostatic adjustment (GIA)). The largest sources of error for Antarctica are the GIA correction, the omission of l=1 terms, nontidal changes in ocean mass, and measurement errors. For Greenland, the errors come mostly from the uncertainty in the scaling factor. Using Release 5.0 (RL05) GRACE fields for January 2003 through November 2012, we find a mass change of −258 ± 41 Gt/yr for Greenland, with an acceleration of −31 ± 6 Gt/yr2, and a loss that migrated clockwise around the ice sheet margin to progressively affect the entire periphery. For Antarctica, we report changes of −83 ± 49 and −147 ± 80 Gt/yr for two GIA models, with an acceleration of −12 ± 9 Gt/yr2and a dominance from the southeast pacific sector of West Antarctica and the Antarctic Peninsula."

[AbruptSLR]

The following two extracts about GIA (post-glacial rebound), and attached image, are taken from Wikipedia:

Extract 1: "Post-glacial rebound (sometimes called continental rebound, glacial isostasy, glacial isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy. It affects northern Europe (especially Scotland, Estonia, Fennoscandia, and northern Denmark), Siberia, Canada, the Great Lakes of Canada and the United States, the coastal region of the US state of Maine, parts of Patagonia, and Antarctica."

Extract 2: "Recent global warming has caused mountain glaciers and the ice sheets in Greenland and Antarctica to melt and global sea level to rise. Therefore, monitoring sea level rise and the mass balance of ice sheets and glaciers allows us to understand more about global warming.
Recent rise in sea levels has been monitored by tide gauges and Satellite Altimetry (e.g. TOPEX/Poseidon). In addition to the addition of melted ice water from glaciers and ice sheets, recent sea level changes are also affected by the thermal expansion of sea water due to global warming, sea level change due to deglaciation of the last Ice Age (postglacial sea level change), deformation of the land and ocean floor and other factors. Thus, to understand global warming from sea level change, one must be able to separate all these factors, especially postglacial rebound, since it is one of the leading factors.
Mass changes of ice sheets can be monitored by measuring changes in the ice surface height, the deformation of the ground below and the changes in the gravity field over the ice sheet. Thus ICESat, GPS and GRACE satellite mission are useful for such purpose. However, glacial isostatic adjustment of the ice sheets affect ground deformation and the gravity field today. Thus understanding glacial isostatic adjustment is important in monitoring recent global warming.
One of the possible impacts of global warming-triggered rebound may be more volcanic activity in previously ice-capped areas such as Iceland and Greenland. It may also trigger intraplate earthquakes near the ice margins of Greenland and Antarctica."

Extract 1 presents a "traditional" view of GIA being due to post-glacial rebound due to ice mass loss since the last glacial maximum, LGM (or Eemian); while the second extract illustrates that the authors fully understand that this "traditional" view of GIA needs to be refined when addressing areas with significant current ice mass loss from ice sheets (or glaciers/icecap), such as WAIS.  The attached figure (from Pauls 2007), shows the "traditional" GIA concept, as explained by the figure caption:

"A model of present-day mass change due to post-glacial rebound and the reloading of the ocean basins with seawater.  Blue and purple areas indicate rising due to the removal of the ice sheets. Yellow and red areas indicate falling as mantle material moved away from these areas in order to supply the rising areas, and because of the collapse of the forebulges around the ice sheets."

As can be seen in the attached image, under the "traditional" GIA theory (per Pauls 2007): (a) in the West Antarctic, large areas of the BSB and of the Weddell Sea coastal glacial basins are still rebounding upward [as magma flows under these sections of crust largely from the adjoining seafloor which is dropping in elevation]; and (b) in the East Antarctic the situation is a bit more complex (although less dynamic) as some areas of continental crust are re-bounding while others are fall, as are all East Antarctic continental shelves.  As noted above, in areas of rapid current ice mass loss/gain this "traditional" GIA theory must be modified to account for these local changes, and thus as note in my Reply # 9 to this thread, NASA has released the relevant GRACE data so that researchers can make their own corrections to the "traditional" GIA data.  Reasons that individual researchers must make their own corrections is because, until more field data is collected, there are differing points of view [see also information in my Replies #15 and 16] as to what local corrections need to be made when considering such matters as: (a) atmospheric river snow fall events; (b) wind driven snow scouring; and (c) the rates at which magma migration occurs [particularly in the West Antarctic which has a very thin and cracked crust, as discussed throughout this thread].

[AbruptSLR]

Per seismic experts at Argentina's Orcadas base (see attached image for the location of the base):

"At 1103 local time (1403 GMT) on Monday, the seismological station ... registered an earthquake measuring 7.3 on the Richter scale in the area near the base, with an epicenter 10 kilometers (six miles) deep," Argentina's Antarctic management said in a statement.
The 7.3 magnitude quake generated large waves but caused no injuries, the team said.
The earthquake did not cause any damage to the base or cause any injuries to the staff, it said, adding there were no reports of damage or injuries at other bases on the Antarctic Peninsula."

The real questions are:
(a) whether a small tsunami from this offshore earthquake may disrupt either the sea ice, or the FRIS, in the Weddell Sea area; and
(b) whether there will be an increasing trend of such large earthquakes triggered by the loss of ice mass from the WAIS (in the image in the immediate preceeding post note the seafloor deformation due to the post-glacial rebound effect).

[SteveMDFP]

Per seismic experts at Argentina's Orcadas base (see attached image for the location of the base):

"At 1103 local time (1403 GMT) on Monday, the seismological station ... registered an earthquake measuring 7.3 on the Richter scale in the area near the base, with an epicenter 10 kilometers (six miles) deep," Argentina's Antarctic management said in a statement.
The 7.3 magnitude quake generated large waves but caused no injuries, the team said.
The earthquake did not cause any damage to the base or cause any injuries to the staff, it said, adding there were no reports of damage or injuries at other bases on the Antarctic Peninsula."

The real questions are:
(a) whether a small tsunami from this offshore earthquake may disrupt either the sea ice, or the FRIS, in the Weddell Sea area; and
(b) whether there will be an increasing trend of such large earthquakes triggered by the loss of ice mass from the WAIS (in the image in the immediate preceeding post note the seafloor deformation due to the post-glacial rebound effect).

USGS rated this quake at 5.7. 
http://earthquake.usgs.gov/earthquakes/eventpage/usb000ifgq#summary

[AbruptSLR]

As a follow-on to my Reply #17, the following references/abstracts indicate the number of variables involved in GIA corrections for Antarctica; thus explaining why there are differences of opinion on what corrections to make, and also why NASA would allow researchers to make their own corrections to the GRACE data:


A deglacial model for Antarctica: geological constraints and glaciological modelling as a basis for a new model of Antarctic glacial isostatic adjustment
Pippa L. Whitehouse, Michael J. Bentley, Anne M. Le Brocq; 2012

Abstract
We present a new reconstruction of the Antarctic Ice Sheets between 20 ka BP and the present day. Our reconstruction is derived using a numerical model to generate a physically-consistent ice surface across the whole of the continent. We define the extent of the ice sheet at five time slices; 20, 15, 10, 5 and 0 ka BP, assuming an equilibrium state for the 20 ka BP time slice, and a transient state for the deglacial time slices. The evolution of the ice sheet within the numerical model is driven by variations in temperature, accumulation rate, and relative sea level. In order to reconstruct the concave profile of the ice sheet in marine-grounded regions, such as the Ross and Weddell Seas, we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams. We find a strong dependence upon the basal sliding parameters, and also the position of the grounding line. We use an extensive data base of geological and glaciological data to constrain our ice-sheet reconstruction. Grounding-line extent is prescribed from marine geological data and we test ice-sheet thickness against onshore geological data at 62 sites. Of the five time slices considered, our 20 ka BP reconstruction is the best constrained by data and has an RMS misfit of 147.6 m when compared to observations of ice thickness change between 20 ka BP and the present day. Across all time slices there are large regions of the ice-sheet which are poorly constrained, especially after 20 ka BP. We estimate the spatial distribution of uncertainty in our ice-sheet reconstruction, and note that the solutions are least reliable in regions of complex topography. We predict that the Antarctic Ice Sheets contributed 9 ± 1.5 m of eustatic sea level to the global ocean between 20 ka BP and the present, and our reconstruction with minimum misfit contributes ∼8 m eustatic sea level during this period. These values, which we argue are an upper bound, are lower than many previous estimates. The reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models

A new glacial isostatic adjustment model for Antarctica: calibrated and tested using observations of relative sea-level change and present-day uplift rates Pippa L. Whitehouse, Michael J. Bentley, Glenn A. Milne, Matt A. King and Ian D. Thomas; 2012

We present a glacial isostatic adjustment (GIA) model for Antarctica. This is driven by a new deglaciation history that has been developed using a numerical ice-sheet model, and is constrained to fit observations of past ice extent. We test the sensitivity of the GIA model to uncertainties in the deglaciation history, and seek earth model parameters that minimize the misfit of model predictions to relative sea-level observations from Antarctica. We find that the relative sea-level predictions are fairly insensitive to changes in lithospheric thickness and lower mantle viscosity, but show high sensitivity to changes in upper mantle viscosity and constrain this value (95 per cent confidence) to lie in the range 0.8–2.0 × 1021 Pa s. Significant misfits at several sites may be due to errors in the deglaciation history, or unmodelled effects of lateral variations in Earth structure. When we compare our GIA model predictions with elastic-corrected GPS uplift rates we find that the predicted rates are biased high (weighted mean bias = 1.8 mm yr−1) and there is a weighted root-mean-square (WRMS) error of 2.9 mm yr−1. In particular, our model systematically over-predicts uplift rates in the Antarctica Peninsula, and we attempt to address this by adjusting the Late Holocene loading history in this region, within the bounds of uncertainty of the deglaciation model. Using this adjusted model the weighted mean bias improves from 1.8 to 1.2 mm yr−1, and the WRMS error is reduced to 2.3 mm yr−1, compared with 4.9 mm yr−1 for ICE-5G v1.2 and 5.0 mm yr−1 for IJ05. Finally, we place spatially variable error bars on our GIA uplift rate predictions, taking into account uncertainties in both the deglaciation history and modelled Earth viscosity structure. This work provides a new GIA correction for the GRACE data in Antarctica, thus permitting more accurate constraints to be placed on current ice-mass change.

[AbruptSLR]

I provide this reference & abstract for those interested in GIA in Antarctica and its implications on GRACE ice mass loss calculations:

http://gji.oxfordjournals.org/content/192/2/557

Computations of the viscoelastic response of a 3-D compressible Earth to surface loading: an application to Glacial Isostatic Adjustment in Antarctica and Canada
by: Geruo A, John Wahr and Shijie Zhong, February 2013, Geophysical Journal International

"We develop a 3-D finite-element model to study the viscoelastic response of a compressible Earth to surface loads. The effects of centre of mass motion, polar wander feedback, and self-consistent ocean loading are implemented. To assess the model's accuracy, we benchmark the numerical results against a semi-analytic solution for spherically symmetric structure. We force our model with the ICE-5G global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment (GIA) observables, including relative sea-level (RSL) measurements in Canada, and present-day time-variable gravity and uplift rates in Antarctica. Canadian RSL observations have been used to determine the Earth's globally averaged viscosity profile. Antarctic GPS uplift rates have been used to constrain Antarctic GIA models. And GIA time-variable gravity and uplift signals are error sources for GRACE and altimeter estimates of present-day Antarctic ice mass loss, and must be modelled and removed from those estimates. Computing GIA results for a 3-D viscosity profile derived from a realistic seismic tomography model, and comparing with results computed for 1-D averages of that 3-D profile, we conclude that: (1) a GIA viscosity model based on Canadian relative sea-level data is more likely to represent a Canadian average than a true global average; (2) the effects of 3-D viscosity structure on GRACE estimates of present-day Antarctic mass loss are probably smaller than the difference between GIA models based on different Antarctic deglaciation histories and (3) the effects of 3-D viscosity structure on Antarctic GPS observations of present-day uplift rate can be significant, and can complicate efforts to use GPS observations to constrain 1-D GIA models."

[sidd]

Fig 3 in Velicogna(2013) is scary

[AbruptSLR]

Sidd,

I agree that the indicated rate of acceleration of ice mass loss (particularly from the WAIS) is scary; particularly when you realize that since about 2000 we been in an El Nino hiatus period (associated with a negative PDO index); and that when the PDO index turn positive the rate of acceleration is bound to increase; perhaps sufficiently to clear the Thwaites Gateway, that could then lead to the Thwaites Effect that I have discussed that could result in such a highly non-linear rate of ice mass loss from the WAIS that Hansen's projections of SLR could come true.

Best,
ASLR

[sidd]

I especially dont like greenland NEGIS waking up, and EAIS stirring, (If you compare the 2nd and third frames of each which show the change from the period 2003-2006 and 2007-2012)

Amery seems to be quieter in the later period, we see the recent increased  snow effects in the atlantic sector, but i dont like totten-cook-moscow u glaciers losing mass faster.  We shall see, probably quicker than I imagine.

[AbruptSLR]

Sidd,

While I am no expert on Greenland, I have read some articles implying that as the GIS marine terminating glacier's GL retreat out of the water, that their rate of ice mass loss will slow; while surface melting/runoff is expected to be more of a long-term problem for the GIS.

Regarding the stirring of the EAIS, I also don't like look of the Totten-Cook-Moscow U. glaciers either.

Best,
ASLR

[AbruptSLR]

While the attached figure of computer projected geothermal basal heat for Antarctica is several years old, and thus the missing scale is now out of date (so I am not including it); nevertheless, I that the pattern of warmer and cooler geothermal basal conditions is instructive of future glacial areas that may become activated for ice mass loss, given a sufficient push from any adjoining present or future warm CDW.

[sidd]

This not the thread for GIS, but I will say that NEGIS bed is very, very, deep, there will be no land refuge there for a while.

[AbruptSLR]

While I could have just as reasonably posted the following in either the "Paleo-evidence" thread, or the "Collapse" thread; it seems most appropriate to note in the "Antarctic Tectonics" thread that the following reference provides paleo-evidence of significant seismic activity induced by ice mass loss during prior interglacial periods; and that we can expect similiar tectonic activity as ice mass loss accelerates this century:

Hampel A, Hetzel R, Maniatis G.,  2010, Response of faults to climate-driven changes in ice and water volumes on Earth's surface, Philos Transact A Math Phys Eng Sci. 2010 May 28;368(1919):2501-17.

Abstract
"Numerical models including one or more faults in a rheologically stratified lithosphere show that climate-induced variations in ice and water volumes on Earth's surface considerably affect the slip evolution of both thrust and normal faults. In general, the slip rate and hence the seismicity of a fault decreases during loading and increases during unloading. Here, we present several case studies to show that a postglacial slip rate increase occurred on faults worldwide in regions where ice caps and lakes decayed at the end of the last glaciation. Of note is that the postglacial amplification of seismicity was not restricted to the areas beneath the large Laurentide and Fennoscandian ice sheets but also occurred in regions affected by smaller ice caps or lakes, e.g. the Basin-and-Range Province. Our results do not only have important consequences for the interpretation of palaeoseismological records from faults in these regions but also for the evaluation of the future seismicity in regions currently affected by deglaciation like Greenland and Antarctica: shrinkage of the modern ice sheets owing to global warming may ultimately lead to an increase in earthquake frequency in these regions."

[AbruptSLR]

The following weblink provides access to a free pdf about monitoring Antarctic tectonic plate motion using GPS measurement, and provides recent data about the measured data:

http://www.sersc.org/journals/IJCA/vol6_no2/20.pdf

Tectonic Motion Monitoring of Antarctica Using GPS Measurements; Joon-Kyu Park, Min-Gyu Kim and Jong-Sin Lee; International Journal of Control and Automation Vol. 6, No. 2, April, 2013

[AbruptSLR]

The linked reference illustrates the vital importance of making high quality GIA corrections to GRACE observations of ice mass loss from the EAIS and particularly from the WAIS.  The link provides a free pdf of the paper:

http://www.the-cryosphere-discuss.net/7/3497/2013/tcd-7-3497-2013.html

Gunter, B. C., Didova, O., Riva, R. E. M., Ligtenberg, S. R. M., Lenaerts, J. T. M., King, M. A., van den Broeke, M. R., and Urban, T.: Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change, The Cryosphere Discuss., 7, 3497-3541, doi:10.5194/tcd-7-3497-2013, 2013.

"Abstract. This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating reprocessed data sets over a longer period of time, and now include a firn densification model to account for firn compaction and surface processes. A range of different GRACE gravity models were evaluated, as well as a new ICESat surface height trend map computed using an overlapping footprint approach. When the GIA models created from the combination approach were compared to in-situ GPS ground station displacements, the vertical rates estimated showed consistently better agreement than existing GIA models. In addition, the new empirically derived GIA rates suggest the presence of strong uplift in the Amundsen Sea and Philippi/Denman sectors, as well as subsidence in large parts of East Antarctica. The total GIA mass change estimates for the entire Antarctic ice sheet ranged from 53 to 100 Gt yr⁻¹, depending on the GRACE solution used, and with an estimated uncertainty of ±40 Gt yr⁻¹. Over the time frame February 2003–October 2009, the corresponding ice mass change showed an average value of −100 ± 44 Gt yr⁻¹ (EA: 5 ± 38, WA: −105 ± 22), consistent with other recent estimates in the literature, with the mass loss mostly concentrated in West Antarctica. The refined approach presented in this study shows the contribution that such data combinations can make towards improving estimates of present day GIA and ice mass change, particularly with respect to determining more reliable uncertainties."

[AbruptSLR]

The linked reference provides valuable data and insight into the short-, and long-,term relationships between sea level and the solid Earth:


http://gsabulletin.gsapubs.org/content/125/7-8/1027.abstract

The solid Earth’s influence on sea level;
by: Clinton P. Conrad; 2013, GSA Bulletin;  doi: 10.1130/B30764.1 v. 125 no. 7-8 p. 1027-1052



"Abstract
Because it lies at the intersection of Earth’s solid, liquid, and gaseous components, sea level links the dynamics of the fluid part of the planet with those of the solid part of the planet. Here, I review the past quarter century of sea-level research and show that the solid components of Earth exert a controlling influence on the amplitudes and patterns of sea-level change across time scales ranging from years to billions of years. On the shortest time scales (10⁰–10² yr), elastic deformation causes the ground surface to uplift instantaneously near deglaciating areas while the sea surface depresses due to diminished gravitational attraction. This produces spatial variations in rates of relative sea-level change (measured relative to the ground surface), with amplitudes of several millimeters per year. These sea-level “fingerprints” are characteristic of (and may help identify) the deglaciation source, and they can have significant societal importance because they will control rates of coastal inundation in the coming century. On time scales of 10³–10⁵ yr, the solid Earth’s time-dependent viscous response to deglaciation also produces spatially varying patterns of relative sea-level change, with centimeters-per-year amplitude, that depend on the time-history of deglaciation. These variations, on average, cause net seafloor subsidence and therefore global sea-level drop. On time scales of 10⁶–10⁸ yr, convection of Earth’s mantle also supports long-wavelength topographic relief that changes as continents migrate and mantle flow patterns evolve. This changing “dynamic topography” causes meters per millions of years of relative sea-level change, even along seemingly “stable” continental margins, which affects all stratigraphic records of Phanerozoic sea level. Nevertheless, several such records indicate sea-level drop of ∼230 m since a mid-Cretaceous highstand, when continental transgressions were occurring worldwide. This global drop results from several factors that combine to expand the “container” volume of the ocean basins. Most importantly, ridge volume decrease since the mid-Cretaceous, caused by an ∼50% slowdown in seafloor spreading rate documented by tectonic reconstructions, explains ∼250 m of sea-level fall. These tectonic changes have been accompanied by a decline in the volume of volcanic edifices on Pacific seafloor, continental convergence above the former Tethys Ocean, and the onset of glaciation, which dropped sea level by ∼40, ∼20, and ∼60 m, respectively. These drops were approximately offset by an increase in the volume of Atlantic sediments and net seafloor uplift by dynamic topography, which each elevated sea level by ∼60 m. Across supercontinental cycles, expected variations in ridge volume, dynamic topography, and continental compression together roughly explain observed sea-level variations throughout Pangean assembly and dispersal. On the longest time scales (10⁹ yr), sea level may change as ocean water is exchanged with reservoirs stored by hydrous minerals within the mantle interior. Mantle cooling during the past few billion years may have accelerated drainage down subduction zones and decreased degassing at mid-ocean ridges, causing enough sea-level drop to impact the Phanerozoic sea-level budget. For all time scales, future advances in the study of sea-level change will result from improved observations of lateral variations in sea-level change, and a better understanding of the solid Earth deformations that cause them."

[AbruptSLR]

The following linked reference discusses research that has direct bearing on many aspects of AIS stability, including on basal geothermal heating beneath the WAIS and on modeling of GIA corrections:

http://geology.gsapubs.org/content/early/2013/08/12/G33409.1

The Mesozoic Victoria Basin: Vanished link between Antarctica and Australia
by: Frank Lisker (corresponding) and Andreas L. Läufer, Dept. of Geosciences, University of Bremen, PF 330 440, 28334 Bremen, Germany. Published online ahead of print on 12 Aug. 2013; http://dx.doi.org/10.1130/G33409.1.

Abstract:
"The Transantarctic Mountains divide the Antarctic continent between the two embayments of Ross Sea and Weddell Sea into East and West Antarctica. With a total length of about 3,500 km and altitudes up to 5 km, they are one of the largest mountain chains in the world. Their origin is traditionally related to episodic uplift since 180 million years ago, with the final, most important uplift episode commencing about 65 million years ago. This concept of a long-lived morphological high constitutes the base of virtually all Gondwana reconstructions and global climate models. This study by Frank Lisker and Andreas L. Läufer demonstrates that crossover age relationships between thermochronological data and stratigraphic information contradict this established interpretation. Instead these data, together with a wealth of independent thermal indicators and geological evidence, require the existence of a vast basin that formed within Gondwana prior to the breakup of the supercontinent. Fast erosion of this "Mesozoic Victoria Basin" about 35 million years ago was isostatically compensated and triggered the uplift of the Transantarctic Mountains. The recognition of the long-lived Mesozoic Victoria Basin has primary consequences for the general understanding of the landscape of Gondwana, the breakup between Antarctica and Australia, the uplift of the Transantarctic Mountains, and global long-term climate evolution and faunal radiation."

[nukefix]

I've been told that models of the lithosphere will improve a lot within a decade as some of the newer GPS-series will become long enough.

[AbruptSLR]

Nukefix,

Thanks for the information.  Obviously, this will be a hot topic for research papers in the coming years as is reflected by the large number of current papers, talks and posters on this topic as illustrated by the following few selected links and information:


http://onlinelibrary.wiley.com/doi/10.1029/AR077p0029/summary

Dalziel, I. W. D. and Lawver, L. A. (2013) The Lithospheric Setting of the West Antarctic Ice Sheet, in The West Antarctic Ice Sheet: Behavior and Environment (eds R. B. Alley and R. A. Bindschadle), American Geophysical Union, Washington, D. C.. doi: 10.1029/AR077p0029


http://iahs-iapso-iaspei2013.com/Abstracts.aspx?252272


3D lithosphere structure of the Antarctic plate and its geodynamical implications on the plate evolution;
by: An, M.; Wiens, D.; Zhao, Y.; Feng, M.; Nyblade, A.; Kanao, M.; Li, Y.; Maggi, A.; Leveque, J; 2013


"Abstract
Seismographs deployed across most of Antarctica since the 4th International Polar Year strongly improved seismic station coverage in the whole continent. Using thousands of fundamental-mode Rayleigh-wave dispersion curves retrieved from the observations of ˜120 seismic stations in Antarctica and surrounding regions, we constructed a 3-D S-velocity model for the lithosphere of the Antarctic plate using a single-step surface-wave tomographic method improved from Feng & An (2010), and then inverted for crust and upper-mantle temperatures using the velocities on the basis of thermoelastic properties of mantle minerals (An & Shi, 2007). A Moho depth map of the continent and a lithosphere-asthenosphere boundary depth map of the entire plate are then retrieved from the velocity and temperature models. The lithosphere of East Antarctica (EANT) is greater than 150 km thick and similar to Precambrian cratons elsewhere, however, the crust beneath the Gamburtsev Subglacial Mountains (GSM) is so thick as to be like a present orogeny. This may imply that the crust/lithosphere beneath the core of EANT have never been transformed after the last orogeny and the ancient orogen structure is still kept today. In contrast, the crust and lithosphere beneath West Antarctica are thin and have been extended during Phanerozoic evolution, and the slab which subducted beneath the Antarctic Peninsula ˜50 My bp cannot be resolved in our models. The oceanic lithosphere of the Antarctic plate is generally thickened as a function of crustal age, and the iso-temperature contour of the lithospheric upper mantle flattens for old regions, in correspondence with the obviously flattening of old seafloor elevations. However, we do not find significant flattening at the lithosphere base if the areas close to the Kerguelen LIP and St. Paul-Amsterdam hotspot are not considered."


http://meetingorganizer.copernicus.org/EGU2013/posters/12534

[AbruptSLR]

The following reference cites evidence of an active volcano that is likely to erupt soon beneath about 1km of ice in the Marie Byrd Land, WAIS, within 30 miles of Mt Sidley (see attached image).  While a sub-glacial eruption in  this area probably would not cause a collapse of the WAIS, such an eruption would probably make a measureable contribution to SLR:

Nature Geoscience, DOI: 10.1038/ngeo1992

http://www.newscientist.com/article/dn24589-seething-volcano-buried-under-antarcticas-ice.html

[AbruptSLR]

The following link references a story about a recent (October of 2013) eruption of Mt Erebus in the Ross Sea.  It is possible that the recent ice mass loss in the WAIS is causing magma to raise, which maybe causing accelerated basal melting, leading to a positive feedback factor between Volcanism and WAIS ice mass loss (see following links):

http://antarcticsun.usap.gov/science/contenthandler.cfm?id=2938

http://www.themalaymailonline.com/features/article/could-volcanoes-be-causing-antarctic-ice-loss

[AbruptSLR]

Now that I am not traveling, I thought that I would post a link, citation and abstract for the newly identified subglacial volcano in Marie Byrd Land.  I also attach an image with a dot showing the location of the new volcano in relation to the Thwaites Drainage Basin, which indicates that any future melt water from the new volcano will drain into the MacAyeal Ice Stream feeding into the Ross Sea (and I note that future melt water may not only come from a subglacial eruption, but also from increasing subglacial geothermal heat in the crust from magma accumulating beneath the volcano):


http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1992.html


"Seismic detection of an active subglacial magmatic complex in Marie Byrd Land, Antarctica"; Amanda C. Lough, Douglas A. Wiens, C. Grace Barcheck, Sridhar Anandakrishnan Richard C. Aster, Donald D. Blankenship, Audrey D. Huerta, Andrew Nyblade, Duncan A. Young & Terry J. Wilson, Nature Geoscience, (2013), doi:10.1038/ngeo1992

Abstract:
"Numerous volcanoes exist in Marie Byrd Land, a highland region of West Antarctica. High heat flow through the crust in this region may influence the stability of the West Antarctic Ice Sheet. Volcanic activity progressed from north to south in the Executive Committee mountain range between the Miocene and Holocene epochs, but there has been no evidence for recent magmatic activit. Here we use a recently deployed seismic network to show that in 2010 and 2011, two swarms of seismic activity occurred at 25–40 km depth beneath subglacial topographic and magnetic highs, located 55 km south of the youngest subaerial volcano in the Executive Committee Range. We interpret the swarm events as deep long-period earthquakes based on their unusual frequency content. Such earthquakes occur beneath active volcanoes, are caused by deep magmatic activity and, in some cases, precede eruptions. We also use radar profiles to identify a prominent ash layer in the ice overlying the seismic swarm. Located at 1,400 m depth, the ash layer is about 8,000 years old and was probably sourced from the nearby Mount Waesche volcano. Together, these observations provide strong evidence for ongoing magmatic activity and demonstrate that volcanism continues to migrate southwards along the Executive Committee Range. Eruptions at this site are unlikely to penetrate the 1.2 to 2-km-thick overlying ice, but would generate large volumes of melt water that could significantly affect ice stream flow."

[TeaPotty]

Hey AbruptSLR,

I read today that there were also eruptions in the 80's, though recent explosions were described as "powerful".

Any idea how strong the activity is now in comparison to the 80's activity?

[AbruptSLR]

TeaPotty,

I am not aware of any definitive papers on this topic, but if you want a paper with a general discussion of the volcanic activity in the West Antaractic then you can look at:

Behrendt, J.C. (2011), "Geophysical evidence of Ice-Magma interactions beneath the West Antarctic Ice Sheet in the West Antarctic Rift System", Proceedings of WAIS workshop.

[AbruptSLR]

The following link leads to an article about new tectonic evidence for West Antarctica, including: (a) indications of a thermal plume in the mantel of Marie Byrd Land; and (b) of an extremely thin crust in the Ross Sea Embayment area.  Such new evidence indicates that the WAIS is more susceptible to basal ice melting than previously thought:

http://www.nbcnews.com/science/giant-blob-hot-rock-hidden-beneath-antarcticas-ice-2D11724262

[AbruptSLR]

The following link leads to an interesting article about research from Ohio State about how East Antarctica is pushing West Antarctica northward at a rate of 1/2 inch per year, which apparently is very fast, and will require substantial corrections to the prior GIA calculations and consequently on the GRACE measured ice mass loss from the WAIS:

http://www.hngn.com/articles/19382/20131211/east-antarctica-sliding-sideways-into-areas-with-most-dramatic-ice-loss.htm

[Shared Humanity]

The following link leads to an interesting article about research from Ohio State about how East Antarctica is pushing West Antarctica northward at a rate of 1/2 inch per year, which apparently is very fast, and will require substantial corrections to the prior GIA calculations and consequently on the GRACE measured ice mass loss from the WAIS:

http://www.hngn.com/articles/19382/20131211/east-antarctica-sliding-sideways-into-areas-with-most-dramatic-ice-loss.htm

I read where the crust between the West Antarctic and East Antarctic is very thin, much like the crust between the Baja peninsula and the rest of Mexico and that this thin crust is where the  earth's mantle is causing new crust to form and causing the two parts of Antarctica to move apart. Given the very thick crust of East Antarctica, couldn't this  movement north be due to this?

[AbruptSLR]

S.H.,

You are right that the West Antarctic crust is very thin with both faults and rift valleys that can both contribute to tectonic plate movement and spreading; nevertheless, these new findings indicate that at the thick East Antarctic crust sinks downward it also pushes the West Antarctic crust laterally (not strictly northward, but largely).  To get the final lateral movement one needs to add-up all of the various sources of West Antarctic crust movement including: (a) rebound of the crust from the last ice age; (b) rebound of the crust due to the current ice mass loss; and (c) motion of the magna in the mantle including upwelling of magma into the recently identified "hot-spot" in Marie Byrd Land, and periodically to various active volanoes.

BR,
ASLR

[Shared Humanity]

Thanks ASLR.

[AbruptSLR]

S.H.,

I forgot to mention that due to the uncertainties of all of these various sources of movement, researchers will be installing more GPS stations around the West Antarctic in order to get a better idea of what changes/movements are happening over time.

Best,
ASLR

[AbruptSLR]

I would like to note that when finding are available from the research cited at the link below, we will know about the risks associated with tectonic activity in Antarctica:

http://antarcticsun.usap.gov/science/contenthandler.cfm?id=2954

[AbruptSLR]

Geologists have produced new map of Antarctica's south Victoria Land and information on how to order this map can be found at the following link:

http://www.voxy.co.nz/national/geologists-produce-new-map-antarcticas-south-victoria-land/5/179876

[AbruptSLR]

The linked article indicates that on October 9th, 2013 Mt Erebus had its largest eruption since 1984:

http://antarcticsun.usap.gov/science/contenthandler.cfm?id=2938

Increasing tectonic activity in West Antarctica could contribute to accelerated ice mass loss in the future.

[AbruptSLR]

While the linked (free access) paper is state of the art (indicating up to 4.5 meters of bed uplift due to GIA for the Pine Island Bay in the next 100-years); I believe that it is likely too conservative scientifically, and that basal melting rates, and earthquakes, will increase ice mass loss faster than the negative feedbacks mentioned in the article:

S. Adhikari, E. Ivins, E. Larour, H. Seroussi, M. Morlighem, and S. Nowicki, (2014), "Future Antarctic bed topography and its implications for ice sheet dynamics", Solid Earth Discuss., 6, 191–228, 2014, www.solid-earth-discuss.net/6/191/2014/; doi:10.5194/sed-6-191-2014

http://www.solid-earth-discuss.net/6/191/2014/sed-6-191-2014-print.pdf

Abstract: "The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) is generally losing its mass since the last glacial maximum (LGM). In a sustained warming climate, the AIS is predicted to retreat at a greater pace primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that the past loading is relatively less important than future loading on the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years 2100 and 2500AD, respectively, and that the East Antarctic Ice Sheet (EAIS) is likely to remain unchanged or subside minimally except around the Amery Ice Shelf.  The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay approaches roughly 45mmyr−1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is associated with the flattening of reverse bed, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote the stability to marine portions of the ice sheet in future."