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Ocean's coldest water disappearing.

A new study published in Journal of Climate suggests that the volume of the coldest deep-ocean water, known as Antarctic bottom water (ABW), has decreased rapidly in recent decades.

ABW is formed as seawater's density increases when the temperature drops (caused by overlying cold air) and salinity rises (due to ice formation). This dense water sinks and flows to deep-ocean regions, where it mixes with warmer waters, a process crucial to the regulation of ocean temperatures and global climate.

Scientists from the National Oceanic and Atmospheric Administration and the University of Washington examined oceanographic surveys carried out from 1980 to 2011 and found that the volume of ABW decreased at a rate of about eight million tonnes per second, the equivalent to 50 times the average flow of the Mississippi River.

'In every oceanographic survey repeated around the Southern Ocean since about the 1980s, ABW has been shrinking at a similar mean rate, giving us confidence that this surprisingly large contraction is robust,' said the study's lead author, Sarah Purkey of the University of Washington.

The authors argue that the Southern Ocean deserves more attention than it receives, as it plays a key role in shaping Earth's climate. It's understood that ABW has been warming and freshening in recent decades, but this study highlights the fact that less of this water has been created when compared to previous decades.

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Title Annotation:Climate Watch
Author:Rustad, Harley
Publication:Geographical
Article Type:Brief article
Geographic Code:8ANTA
Date:May 1, 2012
Words:229
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