In the waters south of Australia from the Antarctic Sea, the tendency of high temperature and low oxygen concentration spreading to the bottom layer and the tendency of low temperature and high oxygen concentration spreading to the mesopelagic zone were confirmed.It was found in a joint research by Tokyo Kaiyo University, Hokkaido University, National Institute of Polar Research, and Shanghai Marine University.
In recent years, low salinity has become widespread mainly in the Antarctic Ocean due to the promotion of melting of glaciers and ice sheets, and it is thought that the cooled seawater, which is the source of Antarctic bottom water, has become less dense.It has been pointed out that the lowering of the density reduces the subduction of cold seawater, resulting in higher temperatures, especially in the bottom layer of the Antarctic Ocean.This also suggests a weakening of the deep general circulation around the globe starting from the subduction of the Antarctic bottom water, and it is feared that it may affect the global heat and mass transport associated with the deep general circulation.
By analyzing the observation results that Tokyokaiyo University's "Umitaka Maru" has continued to carry out since 2010 and past ocean observation data from countries around the world, the actual state of such changes in the ocean was captured. Not only is the tendency for higher temperature and lower oxygen concentration to be stronger in the bottom layer deeper than 4000 m, but also the tendency for lower temperature and higher oxygen concentration to be stronger in the mesopelagic zone from 1000 m to 4000 m in the Antarctic Ocean to the south of Australia. It is said that it was accepted.In other words, a "transformation" of the deep general circulation was found in which a large amount of low-temperature, high-oxygen-concentrated seawater that could not sink into the bottom layer spread in a large amount in the shallower mesopelagic zone.The tendency of low-temperature and high-oxygen concentrations in the mesopelagic zone to extend to the waters south of Australia also indicates that the effects of weakening subduction of Antarctic bottom water are spreading beyond the Antarctic Ocean.
If the Antarctic Ocean continues to undergo low-salt differentiation and shallow subduction, the transport of heat and carbon will change significantly due to changes in the deep general circulation, which may lead to unpredictable climate change. ..A research group led by Assistant Professor Keisuke Shimada of Tokyokaiyo University says that it is necessary to continue to maintain the Umitaka Maru's observations of the Antarctic Ocean and keep an eye on the dynamics of change.
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