Competing influences of the ocean, atmosphere and solid earth on transient Miocene Antarctic ice sheet variability

• Main Authors: Stap, Lennert Bastiaan, Berends, Constantijn J., Scherrenberg, Meike D. W., Wal, Roderik S. W., Gasson, Edward G. W.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Antarctic; The Antarctic; Antarc*; Ice Sheet; Ice Shelf
• Online Access: https://doi.org/10.5194/tc-2021-309; https://tc.copernicus.org/preprints/tc-2021-309/

Benthic δ 18 O levels vary strongly during the warmer-than-modern early- and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS). So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO 2 levels and orbital settings. Earlier transient simulations lacked ice-sheet-atmosphere interactions, and used a present-day rather than Miocene Antarctic bedrock topography. Here, we quantify the effect of ice-sheet-atmosphere interactions, running IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS. Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO 2 levels (between 280 and 840 ppm) as well as ice sheet configurations (between no ice and a large ice sheet). We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography. We find that the positive albedo-temperature feedback, partly compensated by the negative ice-volume-precipitation feedback, increases hysteresis in the relation between CO 2 and ice volume (V). Together, these ice-sheet-atmosphere interactions decrease the amplitude of AIS variability caused by 40-kyr forcing CO 2 cycles by 21 % in transient simulations. Thereby, they also diminish the contribution of AIS variability to benthic δ 18 O fluctuations. Furthermore, we show that under equal atmospheric and oceanic forcing, the amplitude of 40-kyr transient AIS variability becomes 10 % smaller during the early- and mid-Miocene, due to the evolving bedrock topography. Lastly, we quantify the influence of ice shelf formation around the Antarctic margins, by comparing simulations with Last Glacial Maximum (LGM) basal melt conditions, to ones in which ice shelf growth is prevented. Ice shelf formation increases hysteresis in the CO 2 -V relation, and amplifies 40-kyr AIS variability by 19 % using LGM basal melt rates, and by 5 % in our reference setting.