Researchers have found a large reduction in the amount of the coldest deep ocean water, called Antarctic Bottom Water, all around the Southern Ocean using data collected from 1980 to 2011. These findings, in a study now online, will likely stimulate new research on the causes of this change.

It was found that Antarctic Bottom Water has been disappearing at an average rate of about eight million metric tons per second over the past few decades, equivalent to about fifty times the average flow of the Mississippi River or about a quarter of the flow of the Gulf Stream in the Florida Straits.

A layer of Antarctic Bottom Water colder than 0ºC (colors, with darkest blue areas having the thickest layer, and white none) covers the ocean floor around Antarctica (center, shaded grey). Rates at which this layer is thinning during the study period (red numbers in meters per decade) are shown for for each deep basin (outlined by thin grey lines). These rates are estimated using data from repeated oceanographic expeditions (ship tracks shown by thick black lines). Note that seawater at the ocean surface stays liquid even at temperatures approaching -2ºC because of its high salt content. (Credit: NOAA)

Antarctic Bottom Water is formed in a few peculiar  locations around Antarctica, where seawater is cooled by the overlying air and made saltier by ice formation. The dense water then sinks to the sea floor and spreads northward, filling most of the deep ocean around the world as it slowly mixes with warmer waters above it.

The world’s deep ocean currents play a critical role in transporting heat and carbon around the planet, thus regulating our climate.Previous studies have shown that the bottom water has been warming and freshening over the past few decades, now these new results suggest that significantly less amount of this bottom water has been formed during that time .

Changes in the temperature, salinity, dissolved oxygen, and dissolved carbon dioxide of this prominent water mass have important ramifications for Earth’s climate, including contributions to sea level rise and the rate of Earth’s heat uptake.

Source:Sciencedaily

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