Deep sea has "fever"

Temperature increase detected in southern Atlantic

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The coldest water that exists at the bottom of the deep sea in the South Atlantic Ocean is getting warmer and warmer. This has now shown a new study of German and Russian scientists. It is still unclear whether this trend has its origin in the Antarctic and how it will affect the global ocean circulation in the long term, the researchers in the international journal "Geophysical Research Letters".

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The measurement of the temperature at key points of the oceans, it could also be called "fever fairs" in the ocean, is an important task of oceanographers. This allows them to detect possible changes in the flows relatively quickly. One of these sites is located east of Rio de Janeiro, in the so-called "Vema Channel", a canyon between the Argentine and Brazilian Basins. The canal at 4500m water depth is only 15 kilometers wide, but unimaginable three million cubic meters of water per second are transported there on the ground to the north. That's 20 times more than the Amazon leads into the Atlantic.

Temperatures rise systematically

The water, also called Antarctic bottom water, comes from the south polar latitudes, where it is formed in the Weddell Sea during the winter. Unlike many surface currents that are driven by the wind, differences in density act as a drive here. The narrow channel allows the flow to swell to about 25 centimeters per second. "At first glance, that does not seem like much, but at these depths it is almost like a storm in the atmosphere, " explains Walter Zenk from the Leibniz Institute of Marine Sciences (IFM-GEOMAR).

The Kiel oceanographer wrote the study together with his colleague Eugene Morozov from the Shirshov Institute of Oceanology in Moscow. "What's remarkable about the data collected by us and our colleagues in over 35 years is that the temperature at these depths is systematically increasing, from less than 0.18 degrees in the 70s to over 0.22 degrees in May 2007, " Zenk continues, "This may sound negligible, but has a significant impact on the density of the transported water, and density differences are responsible for the inter-deepwater basin interchange." display

Blame climate change?

Is it possible to measure so accurately? "Yes, " confirms Zenk, "our instruments can even measure temperature differences of three thousandths of a degree." Still remains to be clarified where the warming is coming from. Zenk is more careful. "From the available data, we can not say clearly whether this is part of a long natural fluctuation or perhaps even here is the global warming. The latter would be possible, because the body of water is only a few decades "old". This is the time that has passed since sinking from the surface in the Antarctic to the arrival in the Vema Channel.

And the consequences? The Antarctic soil water is part of a global ocean circulation that circulates water masses on a time scale of centuries. If these global upheavals change, this also has a long-term effect on our climate. So, bottom water in the Vema Channel is a small but important piece of the mosaic in this global game. Walter Zenk and his colleagues will continue to measure "fever" to shed some light on the depths of the deep sea and its secrets.

(idw - Leibniz Institute of Marine Sciences, 30.07.2007 - DLO)