Past continental shelf evolution increased Antarctic ice sheet sensitivity to climatic conditions

Florence Colleoni,Nigel Wardell,Philip J Bart,Enea Montoli,Laura De Santis,Stefano Prato,Elisabetta Olivo,Andrea Bergamasco,Edward G W Gasson,Chiara Sauli,Christopher C Sorlien

doi:10.1038/s41598-018-29718-7

Abstract

Over the past 34 Million years, the Antarctic continental shelf has gradually deepened due to ice sheet loading, thermal subsidence, and erosion from repeated glaciations. The deepening that is recorded in the sedimentary deposits around the Antarctic margin indicates that after the mid-Miocene Climate Optimum (≈15 Ma), Antarctic Ice Sheet (AIS) dynamical response to climate conditions changed. We explore end-members for maximum AIS extent, based on ice-sheet simulations of a late-Pleistocene and a mid-Miocene glaciation. Fundamental dynamical differences emerge as a consequence of atmospheric forcing, eustatic sea level and continental shelf evolution. We show that the AIS contributed to the amplification of its own sensitivity to ocean forcing by gradually expanding and eroding the continental shelf, that probably changed its tipping points through time. The lack of past topographic and bathymetric reconstructions implies that so far, we still have an incomplete understanding of AIS fast response to past warm climate conditions, which is crucial to constrain its future evolution.

Highlights

Over the past 34 Million years, the Antarctic continental shelf has gradually deepened due to ice sheet loading, thermal subsidence, and erosion from repeated glaciations
Our results show that the gradual deepening of the outer continental shelf from Eocene-Oligocene Antarctic reconstruction6 (EOT) to RBEDMAP2 induces an overall gradual decrease in ice volume along with increasing calving and sub-ice-shelf melting
Our simulations clearly show that the evolution of the deepening and expansion of the continental margins influences the dynamical states of the Antarctic Ice Sheet (AIS), independently from the atmospheric forcing (Fig. 3)

Summary

Introduction

Over the past 34 Million years, the Antarctic continental shelf has gradually deepened due to ice sheet loading, thermal subsidence, and erosion from repeated glaciations. The first mid-Miocene topography, SHALLOW_MIO, assumes that most of the deepening of WAIS and of East Antarctica (EAIS) marine basins, including the filling and expansion of the outer-most margins, occurs after the MCO (upper bound of the mid-Miocene glacial erosional event) It still has very shallow bathymetry (most of West Antarctica is emerged) and relatively-smaller continental shelves at 15 Ma (Fig. 1c). SHALLOW_MIO is considered as an earlier stage of continental shelf expansion relatively to DEEP_MIO We use these four topographies (EOT, SHALLOW_ MIO, DEEP_MIO, and RBEDMAP2) as boundary conditions for ice sheet simulations to test the impact of the gradual deepening and expansion of the continental shelf on the AIS dynamics and its response to mid-Miocene and late-Pleistocene glacial climate conditions as well as to different sub-ice-shelf melting and calving conditions

Methods

Results

Conclusion