USAP-DC

Overview: Several recent studies indicate continuing and increasing ice loss from the Amundsen Sea region of West Antarctica (chiefly Pine Island and Thwaites glaciers). This loss is initiated by thinning of the floating ice shelves by basal melting driven by circulation of relatively warm ocean water under the ice shelves. This thinning triggers ice-dynamics related feedbacks, which leads to loss of ice from the grounded ice sheet. Models suggest that, even though long-term committed ice loss might be governed by ice dynamics, the magnitude of ocean-driven melting at the base of the ice shelves plays a critical role in controlling the rate of ice loss. These conclusions, however, are based on simple parameterized models for melt rate that do not take into account how ocean circulation will change in future as large-scale climate forcing changes, and as the ice shelves thin and retreat through both excess melting and accelerated ice flow. Given that present global climate models struggle to resolve the modern ocean state close to the ice shelves around Antarctica, their projections of future impacts on basal melting and time scale of ice loss have large uncertainties. This project is aimed at reducing these uncertainties though two approaches: (i) assessing, for a given ocean state, how the melt rates will change as ice-shelf cavities evolve through melting and grounding-line retreat, and (ii) improving understanding of the sensitivity of melt rates beneath the Pine Island and Thwaites ice shelves to changes in ocean state on the Amundsen Sea continental shelf. These studies will provide more realistic bounds on ice loss and sea level rise, and lay the groundwork for development of future fully-coupled ice sheet-ocean simulations. Intellectual Merit: Rather than pursue a strategy of using fully coupled models, this project adopts a simpler semi-coupled approach to understand the sensitivity of ice-shelf melting to future forcing. Specifically, the project focuses on using regional ocean circulation models to understand current and future patterns of melting in ice-shelf cavities. The project’s preliminary stage will focus on developing high-resolution ice-shelf cavity-circulation models driven by modern observed regional ocean state and validated with current patterns of melt inferred from satellite observations. Next, an ice-flow model will be used to estimate the future grounding line at various stages of retreat. Using these results, an iterative process with the ocean-circulation and ice-flow models will be applied to determine melt rates at each stage of grounding line retreat. These results will help assess whether more physically constrained melt-rate estimates substantially alter the hypothesis that unstable collapse of the Amundsen Sea sector of West Antarctica is underway. Further, by multiple simulations with modified open-ocean boundary conditions, this study will provide a better understanding of the sensitivity of melt to future changes in regional forcing. For example, what is the sensitivity of melt to changes in Circumpolar Deep Water temperature and to changes in the thermocline height driven be changes in wind forcing? Finally, several semi-coupled ice-ocean simulations will be used to investigate the influence of the ocean-circulation driven distribution of melt over the next several decades. These simulations will provide a much-improved understanding of the linkages between far-field ocean forcing, cavity circulation and melting, and ice-sheet response. Broader Impacts: Planning within the current large range of uncertainty in future sea level change leads to high social and economic costs for governments and businesses worldwide. Thus, our project to reduce sea-level rise uncertainty has strong societal as well as scientific interest. The findings and methods will be applicable to ice shelf cavities in other parts of Antarctica and northern Greenland, and will set the stage for future studies with fully coupled models as computational resources improve. This interdisciplinary work combines expertise of glaciologists and oceanographers, and will contribute to the education of new researchers in this field, with participation of graduate students and postdocs. Through several outreach activities, team members will help make the public aware of the dramatic changes occurring in Antarctica along with the likely consequences. This proposal does not require fieldwork in the Antarctic.

Person	Role
Joughin, Ian	Investigator and contact
Dutrieux, Pierre	Co-Investigator
Padman, Laurence	Investigator
Springer, Scott	Co-Investigator

Antarctic Glaciology	Award # 1643285
Antarctic Integrated System Science	Award # 1643285
Antarctic Ocean and Atmospheric Sciences	Award # 1643285
Antarctic Glaciology	Award # 1643174
Antarctic Integrated System Science	Award # 1643174
Antarctic Ocean and Atmospheric Sciences	Award # 1643174

USAP-1643285_1

None in the Database

Repository	Title (link)	Format(s)	Status
Uni. Washington ResearchWorks Archive	Data associated with Ice-Shelf Retreat Drives Recent Pine Island Glacier Speedup and Ocean-Induced Melt Volume Directly Paces Ice Loss from Pine Island Glacier	Excel	exists
GitHub	Beta Version of Plume Model	None	exists
GitHub	icepack	None	exists
GitHub	Pine Island Basin Scale Model	None	exists

1. Selley, H. L., Hogg, A. E., Cornford, S., Dutrieux, P., Shepherd, A., Wuite, J., Floricioiu, D., Kusk, A., Nagler, T., Gilbert, L., Slater, T., & Kim, T.-W. (2021). Widespread increase in dynamic imbalance in the Getz region of Antarctica from 1994 to 2018. Nature Communications, 12(1). https://doi.org/10.1038/s41467-021-21321-1 (doi:10.1038/s41467-021-21321-1)
2. Davis, P. E. D., Jenkins, A., Nicholls, K. W., Brennan, P. V., Abrahamsen, E. P., Heywood, K. J., Dutrieux, P., Cho, K., & Kim, T. (2018). Variability in Basal Melting Beneath Pine Island Ice Shelf on Weekly to Monthly Timescales. Journal of Geophysical Research: Oceans, 123(11), 8655–8669. Portico. https://doi.org/10.1029/2018jc014464 (doi:10.1029/2018jc014464)
3. Shapero, D. R., Badgeley, J. A., Hoffman, A. O., & Joughin, I. R. (2021). icepack: a new glacier flow modeling package in Python, version 1.0. Geoscientific Model Development, 14(7), 4593–4616. https://doi.org/10.5194/gmd-14-4593-2021 (doi:10.5194/gmd-14-4593-2021)
4. Springer, S., Mack, S., Dutrieux, P., Padman, L., Joughin, I., & Shean, D. (2020). Dependence of Pine Island Glacier Ice Shelf Basal Melt Rates on Subgrid-Scale Parameterizations of Mixing. https://doi.org/10.1002/essoar.10503807.1 (doi:https://doi.org/10.1002/essoar.10503807.1)
5. Arnscheidt, Constantin W. and Marshall, John and Dutrieux, Pierre and Rye, Craig D. and Ramadhan, Ali. (2021). On the settling depth of meltwater escaping from beneath Antarctic ice shelves. Journal of Physical Oceanography. . Status = Deposited in NSF-PAR doi:https://doi.org/10.1175/JPO-D-20-0286.1 ; Federal Government's License = Acknowledged. (Completed by Joughin, Ian on 07/28/2022 ) (doi:10.1002/essoar.10503807.1)
6. Jenkins, Adrian and Shoosmith, Deb and Dutrieux, Pierre and Jacobs, Stan and Kim, Tae Wan and Lee, Sang Hoon and Ha, Ho Kyung and Stammerjohn, Sharon. (2018). West Antarctic Ice Sheet retreat in the Amundsen Sea driven by decadal oceanic variability. Nature Geoscience. 11 (10) 733 to 738. (doi: doi:https://doi.org/10.1038/s41561-018-0207-4 )
7. Joughin, Ian and Shapero, Daniel and Smith, Ben and Dutrieux, Pierre and Barham, Mark. (2021). Ice-shelf retreat drives recent Pine Island Glacier speedup. Science Advances. 7 (24) .. (doi:https://doi.org/10.1126/sciadv.abg3080)
8. Joughin, Ian and Shapero, Daniel and Dutrieux, Pierre and Smith, Ben. (2021). Ocean-induced melt volume directly paces ice loss from Pine Island Glacier. Science Advances. 7 (43) (doi: doi:https://doi.org/10.1126/sciadv.abi5738)
9. Kim, Tae‐Wan and Yang, Hee Won and Dutrieux, Pierre and Wåhlin, Anna K. and Jenkins, Adrian and Kim, Yeong Gi and Ha, Ho Kyung and Kim, Chang‐Sin and Cho, Kyoung‐Ho and Park, Taewook and Park, Jisoo and Lee, SangHoon and Cho, Yang‐Ki. (2021). Interannual Variation of Modified Circumpolar Deep Water in the Dotson‐Getz Trough, West Antarctica. Journal of Geophysical Research: Oceans. 126 (12) . (doi:https://doi.org/10.1029/2021JC017491 )
10. Holland, Paul R. and Bracegirdle, Thomas J. and Dutrieux, Pierre and Jenkins, Adrian and Steig, Eric J.. (2019). West Antarctic ice loss influenced by internal climate variability and anthropogenic forcing. Nature Geoscience. 12 (9) 718 to 724. (doi: doi:10.1038/s41561-019-0420-9)
11. Shean, David E. and Joughin, Ian R. and Dutrieux, Pierre and Smith, Benjamin E. and Berthier, Etienne. (2018). Ice shelf basal melt rates from a high-resolution DEM record for Pine Island Glacier, Antarctica. The Cryosphere Discussions. 1 to 39 (doi: doi:10.5194/tc-2018-209)
12. Shapero, D., Badgeley, J., Hoffmann, A., & Joughin, I. (2021). <i>icepack</i>: a new glacier flow modeling package in Python, version 1.0. (doi:10.5194/gmd-2020-419)