Science.-A tectonic shift in the Southern Ocean led to frozen Antarctica

11-24-2021 The edge of an Antarctic ice sheet on the coast of the vast continent, surrounded by the Southern Ocean. Image captured in 2017. RESEARCH AND TECHNOLOGY POLICY UNIVERSITY OF LEICESTER / KATHARINA HOCHMUTH


A sudden cooling event 34 million years ago that contributed to the formation of the Antarctic ice sheets had a tectonic origin.

High-resolution simulations of ocean circulations show that the tectonic opening of the Southern Ocean sea lanes caused a fundamental reorganization of ocean currents, the transport of heat and initiated a strong cooling of the Antarctic surface water of up to 5 degrees Celsius. .

The study, conducted by an international team of researchers from the University of Leicester, the Netherlands, Australia, Germany and Norway, is published in Nature Communications. The results shed new light on a 50-year-old question about how and why the Antarctic ice sheets formed.

Dr Katharina Hochmuth, Research Associate with the International Ocean Discovery Program (IODP) at the University of Leicester and co-author of the study, said in a statement: “In the last week and in the lead up to COP26, we have heard a lot on modeling projections about the future of our planet In this paper, we show that it is crucial to include atmospheric CO2 conditions, as well as appropriate geographies from the past, to successfully model climate change.

“A 600-meter change in the depth of a gateway to the ocean can cause a dramatic drop in coastal temperatures and thus the fate of the Antarctic ice sheet.”

The last land bridges connecting Antarctica to the surrounding continents, Australia and South America, were broken about 34 million years ago. This tectonic event not only left the polar continent isolated by other land masses; it also led to a major reorganization of ocean currents in the Southern Ocean.

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A circumpolar current began to flow, preventing the subpolar gyres from carrying warm surface waters to the Antarctic coast. At the same time, ice sheets began to accumulate in Antarctica and the Earth experienced one of its most fundamental climate change events, moving from warm greenhouse conditions to cold ice conditions.

The authors’ high-resolution ocean simulations show that only a small deepening of the Southern Ocean sea lanes by a few hundred meters led to a dramatic cooling of Antarctic surface waters. Along with declining atmospheric carbon dioxide (CO2) concentrations, this tectonic event played a crucial role in the first Antarctic ice age and in Earth’s transition to an Icehouse world.

The results presented in this study demonstrate the importance of tectonic-driven processes in the changing oceanographic and climatic conditions of the Southern Ocean.

Understanding these ancient climate stages is crucial to validating climate models that predict future climate conditions and understanding how the climate might behave in higher concentrations of atmospheric carbon dioxide (CO2).

Myrtle Frost

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