Were the Cook and Ninnis glaciers stable in the Pleistocene?

The thick and cold East Antarctic Ice Sheet (EAIS) is apparently stable and melts only slightly due to atmospheric warming. However, it is predicted that the EAIS sectors, whose base is below sea level, will partially shrink or retreat over the next three centuries, mainly due to ocean warming. One of these sectors is located in George V Land (GVL), where ice flow and ice mass loss have increased in recent decades. The intrusion of warm Circumantarctic Deep Water (CDW) was observed between 1996 and 2019 in the mid-continental shelf of GVL off the Ninnis Glacier, but did not reach the subglacial sea cave. Whether and when this phenomenon will progress and lead to ice melt and dynamic changes in the GVL sector remains to be proven.

We present a new geomorphologic map and sedimentary paleoceanographic archives obtained from the GVL continental margin in front of the Cook and Ninnis glaciers by the Cook glacier-Ocean Antarctic Past Stability (COLLAPSE) project funded by the Italian Antarctic Research Program (PNRA), providing evidence for their fluctuations and instability during the Pleistocene. Our results show that the Cook and Ninnis glaciers responded to increased continental shelf warming with partial melting and calving.

Our analysis reconstructs the erosion and deposition processes on the continental slope and sheds light on the dynamics of the EAIS and its interaction with the bottom current during warmer periods with increased CDW rise on the slope. The Pleistocene was the coldest period of the last 100 million years on Earth, during which the Antarctic ice sheet remained roughly stable even during the interglacials. The global sea level change was mainly caused by the volume fluctuations of the Northern Hemisphere ice sheet. Our results show that the marine EAIS sector of the GVL responded to ocean warming and thus contributed to global sea level changes, although major ice mass loss occurred before MIS 9, possibly as a consequence of prolonged warm climate periods such as MIS11.