With the help of the Meteor’s data, the researchers in Hamburg can accurately quantify the temperature changes: Since the time of the expedition, the surface of the Atlantic has grown nearly one degree Celsius warmer, and the total volume of the water in the Atlantic is now 0.12 degrees warmer. “That may sound like a tiny number, but when you consider the enormous volume of water involved, it means that overall the amount of heat has risen considerably over the past 88 years,” explains Gouretski.
The water has primarily grown warmer in the uppermost 2,000 meters, where it has also become saltier. At the same time, under the 2,000-meter mark it has cooled slightly, which leads researchers to believe that the ocean water has substantially expanded, as a result of which the sea level has risen by roughly four centimeters since the beginning of the 20th century. On the basis of their analyses of Meteor’s observations and further historical data, they surmise that the warming of the Atlantic didn’t set in until the early 20th century; before that time, our climate system hadn’t yet reacted to man-made changes, e.g. in the course of the Industrial Revolution.
In the Meteor expedition in the 1920s, the scientists took samples from an area covering roughly 60 million square kilometers, which amounts to 16 percent of the entire ocean. In order to do so, the ship sailed coast-to-coast thirteen times, from the southern reaches to the tropical latitudes of the North Atlantic. It was also the first major expedition to consistently measure the ocean from the surface down to the seabed. In the process, they gathered observational data that remained unmatched in its scope until the 1990s. “But the amount of work involved was no laughing matter,” explains Gouretski. “Whereas today we can electronically control our equipment with the push of a button, they had a fairly hard time gathering data on the small steamer, especially in stormy weather.”
Gouretski and his colleagues from the Max Planck Institute for Meteorology recently published the analysis of the historical data in the academic journal Geophysical Research Letters. The article was selected as a Research Spotlight by the American Geophysical Union.
Viktor Gouretski, Johann H. Jungclaus and Helmuth Haak, 2013, Geophysical Research Letters: Revisiting the Meteor 1925-27 hydrographic dataset reveals centennial full-depth changes in the Atlantic Ocean
Fritz Spiess et al., 1932: Wissenschaftliche Ergebnisse der Deutschen Atlantischen Expedition auf dem Forschungs- und Vermessungsschiff METEOR
Dr. Viktor Gouretski
Integrated Climate Data Center
Cluster of Integrated Climate System Analysis and Prediction CliSAP
CEN, University of Hamburg
Tel.: +49 (0)40 42838-7582