The linked (open access) Fogwill et. al. (2015) reference first notes that in order to achieve the observed sea levels during recent past interglacial periods (particularly the Eemian) as yet unidentified mechanisms must have contributed to the accelerated collapse of major portions of the WAIS. The reference then assumes various collapse scenarios for the WAIS and uses a regional climate model to study the sensitivity of the Southern Ocean to the assumed scenarios in order to study one of several likely feedback mechanisms that could contribute to accelerated WAIS collapse. The attached image shows the projected decrease in AABW formation and the increase in CDW (400 to 700m deep) temperature associated with these scenarios. Of particular, concern is that the projections indicate that the scenarios result in the advection of the warmer CDW to key marine glaciers (notable those in the ASE), which results in a positive feedback for sustained WAIS collapse. The authors acknowledge that their findings are likely conservative (ESLD) as they do not consider continued GHG emissions nor possible high values for ECS/ESS, nor the positive feedbacks cited by Hansen et. al. (2015). The reference concludes by calling for the development of more advanced climate models (such as ACME [both initial and final]) to further investigate the many and complex issues associated with this matter:
C. J. Fogwill, S. J. Phipps, C. S. M. Turney & N. R. Golledge (2015), "Sensitivity of the Southern Ocean to enhanced regional Antarctic ice sheet meltwater input", Earth's Future, Volume 3, Issue 10, Pages 317–329, DOI: 10.1002/2015EF000306
http://onlinelibrary.wiley.com/doi/10.1002/2015EF000306/fullAbstract: "Despite advances in our understanding of the processes driving contemporary sea level rise, the stability of the Antarctic ice sheets and their contribution to sea level under projected future warming remains uncertain due to the influence of strong ice-climate feedbacks. Disentangling these feedbacks is key to reducing uncertainty. Here we present a series of climate system model simulations that explore the potential effects of increased West Antarctic Ice Sheet (WAIS) meltwater flux on Southern Ocean dynamics. We project future changes driven by sectors of the WAIS, delivering spatially and temporally variable meltwater flux into the Amundsen, Ross, and Weddell embayments over future centuries. Focusing on the Amundsen Sea sector of the WAIS over the next 200 years, we demonstrate that the enhanced meltwater flux rapidly stratifies surface waters, resulting in a significant decrease in the rate of Antarctic Bottom Water (AABW) formation. This triggers rapid pervasive ocean warming (>1°C) at depth due to advection from the original site(s) of meltwater input. The greatest warming is predicted along sectors of the ice sheet that are highly sensitized to ocean forcing, creating a feedback loop that could enhance basal ice shelf melting and grounding line retreat. Given that we do not include the effects of rising CO2—predicted to further reduce AABW formation—our experiments highlight the urgent need to develop a new generation of fully coupled ice sheet climate models, which include feedback mechanisms such as this, to reduce uncertainty in climate and sea level projections."
Extract: "One major uncertainty, however, is how the marine-based West Antarctic Ice Sheet (WAIS) will respond to future climate change, and particularly how it may contribute to future global mean sea level (GMSL) [Lenton et al., 2008; Pritchard et al., 2012; Vaughan et al., 2013; Golledge et al., 2015]. In part, this question arises from analogy with past interglacial periods when, despite only small apparent increases in mean atmospheric and ocean temperatures, GMSL is predicted to have been far higher than present [Dutton et al., 2015; Dutton and Lambeck, 2012; Kopp et al., 2009]. To achieve these levels, undefined mechanisms must have been at work that substantially increased the net contribution of the Earth's ice sheets to global sea level [Fogwill et al., 2014].
One such mechanism could have been through ice-ocean feedbacks that arose as a consequence of enhanced meltwater discharge to the Southern Ocean. This has been highlighted in recent studies investigating the apparent coupling between Antarctic ice sheet change and atmospheric temperatures during past interglacials [Holden et al., 2010]. In conclusion, this detailed study of the Last Interglacial demonstrated that feedbacks from WAIS retreat were required to simulate the magnitude of the observed warming within Antarctic ice core records.
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To summarize, the changes in the properties of AABW triggered by increasing freshwater input in the Southern Ocean surrounding Antarctica have critical implications for the dynamics of the Antarctic ice sheet. Intriguingly, several recent studies provide growing evidence of rapid contemporary changes in the properties of AABW [Jacobs et al., 2002; Rhein et al., 2013; van Wijk and Rintoul, 2014]. Observations suggest that the AABW layer is warming, freshening, and contracting in volume [Jacobs et al., 2002], although the drivers of these changes are not yet clear. Our simulations and the mechanism described above suggests that contemporary Southern Ocean freshening may already be occurring as a result of increasing delivery of meltwater from Antarctic ice, with the possibility that a marked reduction in the rate of AABW production may be imminent [Purkey and Johnson, 2013; Rhein et al., 2013], triggering further warming at depth in the Southern Ocean. When combined with uncertainties regarding potential increases in ocean temperatures due to shifting winds and/or changing ocean circulation patterns, the potential for marked changes in ocean ice sheet dynamics over the next century is high [Fogwill et al., 2014; Hellmer et al., 2012; Miles et al., 2013; Spence et al., 2014]. Our experiments provide a unique insight into potential future changes in the Southern Ocean that have important implications for the stability of the Antarctic ice sheets. This study examines just one of a number of strong feedback mechanisms operating at the ocean ice sheet interface that question current sea level rise projections; clearly, modeling studies will need to integrate these feedbacks to gain a more realistic picture of future change."
See also:
Sullivan, C. (2016), Antarctic meltwater makes the ocean warmer and fresher, Eos, 97, doi:10.1029/2016EO044811. Published on 1 February 2016.
https://eos.org/research-spotlights/antarctic-meltwater-makes-the-ocean-warmer-and-fresherExtract: "It’s well known that anthropogenic warming will affect global climate and sea levels far into the future. At the edges of ice sheets and glaciers, water, air, and ice all come together in a complex union that carries implications for predicting climate in the future. As global temperatures rise, ice sheets and glaciers melt, dumping their meltwater into the ocean. The future of some areas, such as the West Antarctic Ice Sheet (WAIS), remains a wildcard when it comes to predicting how the oceans might change.
The WAIS spans much of West Antarctica and holds 2.2 million square kilometers of ice. To try and piece together how the ice sheet might change in the future, Fogwill et al. used climate models to examine the meltwater’s potential effects, focusing on three specific Antarctic regions: the Amundsen, Ross, and Weddell embayments. The scientists’ experiments considered numerous scenarios, ranging from only portions of the ice sheet disappearing to complete melting.
Fresh water flowing off the ice sheet reduces the salinity and density of the ocean’s surface water. With lower-density water sitting on top, the ocean’s vertical layers become more distinct and don’t mix as much. The researchers also found that the formation rate of Antarctic Bottom Water—a layer of dense cool water that pools near the ocean floor—decreased by 25%–50% within decades when compared to a preindustrial control. In all scenarios, the results show that waters ranging from 400 to 700 meters in depth will warm rapidly within the first 200 years, with warming at depth fluctuating between 0.5°C and >1°C, depending on the scenario.
The scientists demonstrated that an increase in fresh meltwater from the WAIS decreases ocean salinity and increases water temperatures in critical locations around the edge of the Antarctic ice sheet, including areas of the East Antarctic Ice Sheet (EAIS). In addition, by investigating specific sites along the ice sheet’s edges, the researchers showed that the location of melting is just as critical to ocean dynamics as the volume of meltwater flowing into the ocean, with sites such as the Amundsen Sea, an area of rapid contemporary WAIS change, being critical.
These effects extend beyond the Southern Ocean. Although the impact is strongest there, all across the Southern Hemisphere, salinity and water temperature are changing. In these models, however, the scientists didn’t include rising atmospheric carbon dioxide levels, which could accelerate the rate of ice sheet melting. Given that, the estimations provided could be conservative."