Nature Communications: Antarctica is covered with ice due to the sinking of the ocean floor global cooling 34 million years ago, which led to the emergence of a thick ice sheet in Antarctica. According to a study published in the journal Nature Communications, the main role in this process was played not only by a decrease in the concentration of carbon dioxide in the Earth's atmosphere, but also by tectonic changes that affected the circulation of seawater in the Southern Ocean.
Traditionally, it is believed that the change from hot greenhouse conditions to a cold climate in the early Cenozoic (from 52 to 34 million years ago) was due to a critical decrease in carbon dioxide in the atmosphere. Known as the Eocene-Oligocene Transition (EOT), these fundamental changes, which determined the state of the Earth's current climate, led to a decrease in the average surface temperature of the entire planet, the expansion of continental glaciers in Antarctica and the emergence of an isolated Antarctic sea ice ecosystem.
However, scientists are debating what role the subsidence of the seabed could have played in the EOT, which opened up the Drake Passage between Antarctica and South America in the Southern Ocean and the Tasmanian Passage, the sea between Australia and Antarctica. Because of this, a circumpolar Antarctic current arose, enveloping Antarctica and passing through all meridians. This current could act as a thermal insulator to keep the Antarctic from warming up. However, modern oceanic models do not confirm that heat transfer to the shores of Antarctica took place at all; therefore, the current should not have influenced the cooling of the South Pole in any way.
In the new work, the researchers developed a higher resolution ocean model than previous models that faithfully reproduced the seabed topography in ancient times, and demonstrated that tectonics did play an important role in the reorganization of heat transport in the Southern Ocean. If at least one sea passage (Tasmanian or Drake Passage) had a depth of less than 300 meters, the sea gyres would transfer warm waters to the shores of Antarctica. When the bottom sank deeper than 300 meters, the gyres sharply weakened, which caused a cooling of surface waters by 2-5 degrees Celsius.
Scientists note that the drop in carbon dioxide levels was probably a decisive factor in the growth of the Antarctic ice sheet. Nevertheless, tectonic processes also influenced the climate of the Southern Ocean and could set threshold values for CO2 concentration below which glaciation of the continent took place. Thus, tectonics must be taken into account in future studies of climate sensitivity to greenhouse gases, the authors conclude.