A joint research group consisting of Hokkaido University, Japan Agency for Marine-Earth Science and Technology, Tokyokaiyo University, and Fisheries Research and Education Agency found that the salt content, which had been declining at an accelerating rate near the bottom of the Antarctic waters south of Australia, reversed sharply in the 2010s. The actual situation that turned to an increase was clarified.The ocean circulation in the deep waters of Antarctica may be strengthening.
Antarctic bottom water is the heaviest water in the ocean that originates along the coast of Antarctica and extends to the bottom of the oceans around the world.It has been pointed out that in the ocean near Antarctica to the south of Australia, the salt content and amount of bottom water decreased from the 1970s to the first half of the 2010s, and the circulation of bottom water may have weakened.It is believed that the background is the increase in freshwater outflow due to the accelerated melting of ice shelves (those that have flowed out from the ice sheet to the sea) in West Antarctica, which is thought to bring about an increase in the average seawater level of the earth.
From December 2018 to March 12, the Fisheries Agency's Kaiyo Maru conducted a wide range of ocean observations from the sea surface to the sea floor in the Antarctic waters.On the other hand, Tokyokaiyo University has been observing the Umitaka Maru on the line along 2019 degrees east longitude to the vicinity of Antarctica for many years.This time, we analyzed the results of high-precision ocean observations by these research vessels together with the results of ocean observations from around the world, and investigated the latest trends in changes in salt content over time.
As a result, the salt content of the bottom layer, which had been declining since the 1970s, reversed in the mid-2010s and rapidly increased in the latter half of the 2010s, and the thickness and amount of bottom water increased.This tendency toward high salinity is stronger near the Ross Sea on the east side and weaker toward the west, indicating that there is a factor of fluctuation on the east side.
This change is believed to be due to the weakening of the Antarctic ice shelves upstream of this area in the early 2010s, indicating a link between the Antarctic ice sheet and the deep sea.In the future, it is necessary to develop an observation network for monitoring the Antarctic Ocean and continue to monitor changes.
Paper information:[Scientific Reports] Reversal of freshening trend of Antarctic Bottom Water in the Australian-Antarctic Basin during 2010s
