The world’s oceans absorb more than 90 percent of the heat that is generated by emissions of greenhouse gas in the atmosphere. They are essential to slow down climate change. In the south, the Atlantic Ocean flows into the Weddell Sea, where gigantic amounts of water are then cooled.

Oceanographers from the Alfred Wegener Institute for Polar – and Marine Research (AWI) found out by means of a long-term data analysis that the deep sea of ​​the Weddell Sea has warmed rapidly in relation to the ocean within three decades. The heat moves through changes in wind and currents in the Southern Ocean from the Antarctic Circumpolar Current – the most powerful cold ocean current in the world – into the deep sea of ​​the Weddel Sea.

Node of ocean circulation The Weddel Sea is the largest of more than a dozen arctic marginal seas of the southern ocean and a crucial crank of the global ocean circulation. When the amounts of water form sea ice, they collect with salt in the so-called overturning movement. Due to their heaviness, they sink into the depths as cold bottom water and pull there as a deep current into the ocean basins.

If the water becomes warmer, it loses density, becomes lighter and rises up in the water column. The greatest change can be measured in the Antarctic bottom water. With far-reaching consequences: Although the Southern Ocean makes up only 15 percent of the world’s ocean surface, it is responsible for around three quarters of the heat storage. Warmed up five times faster than the deep world ocean AWI oceanographers have been drawing since 30 years of temperature and salinity. With a so-called CTD probe (English for “Conductivity”, “Temperature”, “Death”), water temperatures and corresponding changes can now be recorded with an accuracy of one ten-thousandth of a degree Celsius. The evaluation of the long-term data showed that the temperature in the Weddell Sea only rises at a depth of 70 meters. “Our data show a clear division of the water column in the Weddell Sea. While the water in the upper 700 meters has hardly warmed up at all, we see in an area-wide temperature increase from 0, 15 to 0, 0024 degrees Celsius per year “, says AWI oceanographer Volker Strass.

Anyone who considers this to be insignificant deviations is wrong. Compared to the atmosphere, the ocean has a thousand times higher heat capacity, which means that the heat absorption is significantly more significant. The oceanographers come to a disturbing conclusion: “If one calculates the rate of warming in watts per square meter from the rise in temperature, it can be seen that the Weddell Sea in the past 30 years at depths of more than 2000 meters has absorbed five times more heat than the world ocean on average. ” In the short term, the further warming of the Weddel Sea would affect large ice shelves that extend to the sea. In the longer term, this would have direct consequences for sea level rise and the global conveyor belt, the ocean currents of all five seas. (bsc)