USAP-DC

A great deal of uncertainty remains over how changes in high-latitude freshwater forcing will impact the stability of global ocean circulation, and in particular the strength of the Atlantic Meridional Overturning Circulation (AMOC) in the next 100-300 years, especially in realistic models. Indeed, it is still not understood whether increased Southern Ocean freshwater forcing will act to intensify the AMOC and warm the Northern Hemisphere or weaken it and trigger a cooling. The requirement to accurately assess climate sensitivity to freshwater forcing is heightened by increasing evidence that the marine-based West Antarctic Ice Sheet (WAIS) is vulnerable to rapid retreat and collapse on multidecadal-to-centennial timescales. Observations collected over the last 30 years indicate that WAIS is losing ice at an accelerated rate and may signal that the ice sheet has already begun a rapid and irreversible collapse. In addition, future simulations of the Antarctic ice sheet by members of our Project Team show the potential for far more rapid Antarctic ice sheet retreat in the future than previously simulated, suggesting that the discharge of enormous fluxes of icebergs and freshwater to the Southern Ocean should be considered a possibility in the near-future. Here, we performed a suite of coupled numerical climate model simulations to more accurately determine the sensitivity of global ocean circulation to freshwater and iceberg discharge from the Antarctic Ice Sheet (AIS) in the future under IPCC RCP scenarios 4.5 and 8.5. In our model, the input of freshwater and ice was provided by a dynamic ice sheet-shelf model that predicts a full collapse of the WAIS in the next ~100 years. Significantly, we find that accounting for Antarctic discharge raises subsurface ocean temperatures by >1°C at the ice sheet grounding line, relative to model simulations that are unable to capture this discharge. In contrast, we find that the increased meltwater causes a dramatic expansion of sea ice and a 2° - 10°C cooling of the surface air and surface ocean temperatures over the Southern Ocean that would have the potential to stabilize/reduce projected future ice sheet melt rates. Our work thus highlights that the future stability of the Antarctic ice sheet will likely be governed by whether any surface cooling can counteract any increased rates of subsurface melt.

Person	Role
Pollard, David	Investigator and contact
Condron, Alan	Investigator
DeConto, Robert	Investigator

Antarctic Integrated System Science	Award # 1443394
Antarctic Integrated System Science	Award # 1443347

USAP-1443394_1

None in the Database

Repository	Title (link)	Format(s)	Status
USAP-DC	Antarctic Ice Sheet simulations for role of freshwater in future warming scenarios	None	exists
USAP-DC	Simulated changes in Southern Ocean salinity	None	exists
USAP-DC	Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming	None	exists

1. DeConto, R.M. and D. Pollard. 2016. Contribution of Antarctica to past and future sea-level rise. Nature, 531, 591-597. (doi:10.1038/nature17145)
2. Pollard, D., R.M. DeConto and R.B. Alley. 2018. A continuum model (PSUMEL1) of ice mélange and its role during retreat of the Antarctic Ice Sheet. Geosci. Model Devel., 11, 5149-5172. (doi:10.5194/gmd-11-5149-2018)
3. Sadai S, Condron A, DeConto R,M., and Pollard D. (2020). Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming. Science Advances, Vol. 6, eaaz1169 (doi:10.1126/sciadv.aaz1169)
4. Ashley, K. E., McKay, R., Etourneau, J., Jimenez-Espejo, F. J., Condron, A., Albot, A., Crosta, X., Riesselman, C., Seki, O., Massé, G., Golledge, N. R., Gasson, E., Lowry, D. P., Barrand, N. E., Johnson, K., Bertler, N., Escutia, C., Dunbar, R., and Bendle, J. A., (2021). Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat, Climate of the Past, 17, 1–19, (doi:10.5194/cp-17-1-2021)
5. DeConto R.M., Pollard, D., Alley, R.B., Velicogna, I., Gasson, E., Gomez, N., Sadai. S., Condron, A., Gilford, D.M., Ashe, E., L., Li, D., and Kopp, R.E. (2021). The Paris Climate Agreement and future sea-level rise from Antarctica, Nature, 593, 83–89. (doi:10.1038/s41586-021-03427-0)
6. Ashley, K. E., Bendle, J. A., McKay, R., Etourneau, J., Jimenez-Espejo, F. J., Condron, A., … Dunbar, R. (2020). Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat. (doi:10.5194/cp-2020-3)
7. Sadai, S., Spector, R. A., DeConto, R., & Gomez, N. (2022). The Paris Agreement and Climate Justice: Inequitable Impacts of Sea Level Rise Associated With Temperature Targets. Earth’s Future, 10(12). Portico. (doi:10.1029/2022ef002940)