Antarctic bottom water layer, the temperature is below zero (dark blue areas indicate very thick, white — a lack of water), cover the bottom of the ocean around Antarctica (center, highlighted in gray). Shows the rate at which this layer waned during the study (meters per decade). Plunge pools separated by thin gray lines. Note: sea water remains liquid even at temperatures close to -2? C, because of the high salt content.
A significant decrease in the number of cold deep water — the so-called Antarctic bottom water — in the Southern Ocean in the years 1980-2000.
Sara Perks at Washington State University, and Gregory Johnson of the National Oceanic and Atmospheric Administration (USA) found that the Antarctic Bottom Water mass decreases at an average rate of about 8 million tons / s, which is about 50 times greater than the average volume flow of Mississippi and four times less Gulf Stream in the Florida Straits.
Antarctic Bottom Water mass is formed in a few places around Antarctica where the sea water is cooled by air and becomes more saline due to the formation of ice. Condense water then sinks to the bottom and flows north, filling part of the ocean's depths greater rigor around the world and slowly mixed with warm overlying layers.
These underlying currents play an important role in transporting heat and carbon, thus regulating the planet's climate. Changes in temperature, salinity, dissolved oxygen and the amount of carbon dioxide has important implications: for example, they affect sea level rise and the rate of absorption of heat the Earth.
Previous studies have shown that in recent decades bottom water warming and freshening. This time, it was found out also that such waters formed less. "We're not sure if this is part of the long-term trend or cycle," — said Mr. Johnson.
Expert also emphasizes that recent studies often focus on currents in the North Atlantic, which is the main indicator of climate change. But the Southern Ocean has undergone significant changes, which also play an important role in the climate cycle.
The analysis uses high-precision temperature measurements carried out on the International Program of oceanographic research ships.
The study is published in the Journal of Climate.
Prepared according to the National Oceanic and Atmospheric Administration of the United States.