"Waterfalls" in the sea more stable than expected

Deep currents in the North Atlantic were also preserved during the Ice Age

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It is considered the most important circulator of global ocean currents: the North Atlantic. If it fails, it will have catastrophic consequences, especially for Europe's climate. Now researchers in "Science" report that this pump has remained stable even in the last ice age contrary to previous assumptions.

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The North Atlantic is a key location in the global system of ocean currents. The incoming saline Gulf Stream water is cooled and thereby increases in density. After all, it's so hard it's rushing deep and flowing equatorially as part of a global circulation pump. Climatologists have been discussing for some time whether and how the deep water pump works under changed climatic conditions.

In a review article for the current issue of the journal "Science", 18 authors from all over the world, including the Bremen geoscientist Stefan Mulitza from MARUM_Research Center Ocean Rims, summarize the current state of research. They come to the conclusion that the waterfalls in the sea - contrary to previous assumptions - during the last ice age were similar to today. However, the deep water then formed further south. The research results serve to develop models for future climate scenarios and to provide more secure forecasts for our climate future.

Hollywood movie scenario realistic?

The Gulf Stream is drying up and a new ice age is breaking over the northern hemisphere in weeks. As far as the scenario of the disaster film "The Day after Tomorrow". Although the time periods in the film are anything but realistic, some of the general statements are true. Not so long ago, climate scientists actually assumed that during the last ice age the Gulf Stream, or more precisely the deep circulation in the North Atlantic, was greatly weakened. This also seemed logical, as the Gulf Stream and its foothills transported as much heat into the North Atlantic as a million large power plants. display

"The research of recent years has shown that even during the last ice age similar depth of deep water in the North Atlantic was formed as today. However, this body of water only circulates to depths of about 2, 000 meters, while today it reaches much lower levels, "explains Dr. Stefan Mulitza from MARUM_Research Center Ocean Borders. "However, the water was colder altogether and thus probably less heat transport. Deep water formation also took place further south, with the result that the warm currents did not reach as far north as they do today. "

Goal: Improve forecasting models

The assumption that the deep circulation during the Ice Age was greatly attenuated was based primarily on the observation that nutrient-rich Antarctic waters were present at a depth that is today characterized by nutrient-poor North Atlantic deep water. "With new indicators, in particular the ratio of the uranium decay products Protactinium and Thorium, we can say today how long certain water masses have been in the North Atlantic, " says Stefan Mulitza. "This makes it possible to determine retroactively how high the rates of water transport were."

The study presented here is only the prelude to a project in which the existing climate models with the facts now collected to be tested for their reliability. For this purpose, a workshop is planned in April 2008. "The current climate models show a wide range of Atlantic circulation patterns during the last Ice Age, when fed with CO2 levels and ice cover during the last ice age. From a stronger to a weaker rate of change in the Atlantic, all variants are represented, "says Stefan Mulitza. "Modeling the circulation correctly during the last Ice Age increases our confidence in their predictions of future climate evolution.

(Kirsten Achenbach / MARUM_Forschungszentrum Ozeanr nder, 11.04.2007 - NPO)