01 Nov 2021

01 Nov 2021

Review status: this preprint is currently under review for the journal TC.

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

Lennert Bastiaan Stap1, Constantijn J. Berends1, Meike D. W. Scherrenberg1, Roderik S. W. van de Wal1,2, and Edward G. W. Gasson3 Lennert Bastiaan Stap et al.
  • 1Institute for Marine and Atmospheric research Utrecht, Utrecht University, 3584 CC Utrecht, the Netherlands
  • 2Faculty of Geosciences, Department of Physical Geography, Utrecht University, Utrecht, the Netherlands
  • 3College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom

Abstract. Benthic δ18O 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 CO2 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 CO2 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 CO2 and ice volume (V). Together, these ice-sheet-atmosphere interactions decrease the amplitude of AIS variability caused by 40-kyr forcing CO2 cycles by 21 % in transient simulations. Thereby, they also diminish the contribution of AIS variability to benthic δ18O 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 CO2-V relation, and amplifies 40-kyr AIS variability by 19 % using LGM basal melt rates, and by 5 % in our reference setting.

Lennert Bastiaan Stap et al.

Status: open (until 27 Dec 2021)

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Lennert Bastiaan Stap et al.

Model code and software

IMAU-ICE v1.1.1-MIO C. J. Berends, and L. B. Stap

Lennert Bastiaan Stap et al.


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Short summary
To gain understanding of how the Antarctic ice sheet responded to CO2 changes during warm climate conditions, we simulate its variability during the Miocene. We include feedbacks between the ice sheet and atmosphere in our model and find that these reduce the amplitude of ice volume variations. Erosion-induced changes of the bedrock below the ice sheet also have a damping effect. In contrast, land-based ice grows thicker when floating ice shelves are formed, amplifying ice volume variability.