A thermometer for the oceans

The average sea temperature is an essential parameter of the global climate - but it is very difficult to measure. At least until now, because an international team of researchers including Empa scientists have now developed a novel method using the concentration of noble gases in the eternal ice. This allows conclusions to be drawn on the changes in sea temperature from the last ice age to the present day, as the researchers report in the current issue of "Nature". The oceans are the largest global heat reservoir. As a result of man-made global warming, the temperature in the global climate system increases; around 90% of the extra heat is absorbed by the oceans. This means that the average sea temperature can tell us a lot about the state of our climate, both today and in the past. However, it is difficult to determine an accurate average value across all sea depths and regions of the world. The results of previous measurement methods heavily depend on location, season or sea depth, which can lead to distorted results. As part of the WAIS Divide Ice Core Project, an international research team led by Bernhard Bereiter from the Scripps Institution of Oceanography - now working at Empa and the University of Bern - has developed a method of measuring ocean temperatures over the last 24'000 years with high accuracy. These measurements have now been published in "Nature". "Our study clearly shows that the basic idea - the connection between the concentration of noble gases in the atmosphere and the average ocean temperature - is correct and that the method works," said Bereiter. Air bubbles in an ice core from the Antarctic: the ice is up to 24'000 years old. Image: Bernhard Bereiter / Scripps Institution of Oceanography / Empa / University of Berne Eternal ice as contemporary witness