USAP-DC

This award supports a project to study the physical processes that synchronize glacial-scale variability between the Northern Hemisphere ice sheets and the Antarctic ice-sheet. Using a coupled numerical ice-sheet earth-system model, the research team will explore the cryospheric responses to past changes in greenhouse gas concentrations and variations in earth's orbit and tilt. First capturing the sensitivity of each individual ice-sheet to these forcings and then determining their joint variability induced by changes in sea level, ocean temperatures and atmospheric circulation, the researchers will quantify the relative roles of local versus remote effects on long-term ice volume variability. The numerical experiments will provide deeper physical insights into the underlying dynamics of past Antarctic ice-volume changes and their contribution to global sea level. Output from the transient earth system model simulations will be directly compared with ice-core data from previous and ongoing drilling efforts, such as West Antarctic Ice Sheet (WAIS) Divide. Specific questions that will be addressed include: 1) Did the high-latitude Southern Hemispheric atmospheric and oceanic climate, relevant to Antarctic ice sheet forcing, respond to local insolation variations, CO2, Northern Hemispheric changes, or a combination thereof?; 2) How did WAIS and East Antarctic Ice Sheet (EAIS) vary through the Last Glacial Termination and into the Holocene (21 ka- present)?; 3) Did the WAIS (or EAIS) contribute to rapid sea-level fluctuations during this period, such as Meltwater Pulse 1A? 4) Did WAIS collapse fully at Stage 5e (~ 125 ka), and what was its timing relative to the maximum Greenland retreat?; and 5) How did the synchronized behavior of Northern Hemisphere and Southern Hemisphere ice-sheet variations affect the strength of North Atlantic Deep Water and Antarctic Bottom Water formation and the respective overturning cells? The transient earth-system model simulations conducted as part of this project will be closely compared with paleo-climate reconstructions from ice cores, sediment cores and terrestrial data. This will generate an integrated understanding of the hemispheric contributions of deglacial climate change, the origin of meltwater pulses, and potential thresholds in the coupled ice-sheet climate system in response to different types of forcings. A well-informed long-term societal response to sea level rise requires a detailed understanding of ice-sheet sensitivities to external forcing. The proposed research will strongly contribute to this task through numerical modeling and paleo-data analysis. The research team will make the resulting model simulations available on the web-based data server at the Asia Pacific Data Research Center (APDRC) to enable further analysis by the scientific community. As part of this project a female graduate student and a postdoctoral researcher will receive training in earth-system and ice-sheet modeling and paleo-climate dynamics. This award has no field work in Antarctica.

Person	Role
Timmermann, Axel	Investigator

Antarctic Glaciology

Award # 1341311

USAP-1341311_1

None in the Database

Repository	Title (link)	Format(s)	Status
IBS Center for Climate Physics ICCP	784 ka transient Antarctic ice-sheet model simulation data	None	exist

1. Freeman, E., Skinner, L. C., Tisserand, A., Dokken, T., Timmermann, A., Menviel, L., & Friedrich, T. (2015). An Atlantic–Pacific ventilation seesaw across the last deglaciation. Earth and Planetary Science Letters, 424, 237–244. (doi:10.1016/j.epsl.2015.05.032)
2. Weldeab, S., Friedrich, T., Timmermann, A., & Schneider, R. R. (2016). Strong middepth warming and weak radiocarbon imprints in the equatorial Atlantic during Heinrich 1 and Younger Dryas. Paleoceanography, 31(8), 1070–1082. (doi:10.1002/2016pa002957)
3. Tigchelaar, M., Timmermann, A., Friedrich, T., Heinemann, M., & Pollard, D. (2019). Nonlinear response of the Antarctic Ice Sheet to late Quaternary sea level and climate forcing. The Cryosphere, 13(10), 2615–2631. (doi:10.5194/tc-13-2615-2019)
4. Tigchelaar, M., Timmermann, A., Pollard, D., Friedrich, T., & Heinemann, M. (2018). Local insolation changes enhance Antarctic interglacials: Insights from an 800,000-year ice sheet simulation with transient climate forcing. Earth and Planetary Science Letters, 495, 69–78. (doi:10.1016/j.epsl.2018.05.004)
5. Tigchelaar, M., & Timmermann, A. (2015). Mechanisms rectifying the annual mean response of tropical Atlantic rainfall to precessional forcing. Climate Dynamics, 47(1-2), 271–293. (doi:10.1007/s00382-015-2835-3)
6. Tigchelaar, M., Timmermann, A., Friedrich, T., Heinemann, M., & Pollard, D. (2019). Nonlinear response of the Antarctic ice sheet to Quaternary sea level and climate forcing. (doi:10.5194/tc-2019-83)
7. Stockhecke, M., Timmermann, A., Kipfer, R., Haug, G. H., Kwiecien, O., Friedrich, T., … Anselmetti, F. S. (2016). Millennial to orbital-scale variations of drought intensity in the Eastern Mediterranean. Quaternary Science Reviews, 133, 77–95. (doi:10.1016/j.quascirev.2015.12.016)