The western South Atlantic's coldest, deepest layer, called the Antarctic Bottom Water, originates in the waters surrounding Antarctica. In the subtropics, most of this current joins water in the Brazil Basin through the Vema Channel, a narrow gorge on the seafloor about 1000 kilometers (600 miles) southeast of Rio de Janeiro.
Zenk and other researchers have made measurements of water temperatures and other parameters of the flow through the Vema Channel during the past 35 years. In this new analysis, he and Morozov find that temperatures in this channel were fairly level before 1992, but that the next 15 years were marked by a warming trend that raised temperatures about 0.0028ºC (0.005 ºF) each year.
Although this trend is seen, the flow's properties through the Vema Channel were highly variable. Nonetheless, the authors use this long record to conjecture that the Antarctic Bottom Water also has undergone slight freshening.
They note that additional long-term studies on deep circulation and water mass properties may help reveal whether abyssal oceans are warming at locations other than choke points such as the Vema Channel.
Title: Decadal warming of the coldest Antarctic Bottom Water flow through the Vema Channel
Authors: Walter Zenk: The Leibniz Institute of Marine Sciences at the University of Kiel (IFM-GEOMAR), Kiel, Germany;
Eugene Morozov: Shirshov Institute of Oceanology, Moscow, Russia.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030340, 2007
Materials provided by American Geophysical Union. Note: Content may be edited for style and length.
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