New Deep-Ocean Profiling Floats Reveal Rapid Decrease in Antarctic Bottom Water

Dr. Taiyo Kobayashi of the Research and Development Center for Global Change at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has examined recent changes in the Antarctic Bottom Water (AABW) off the Adélie/George V Land coast.

His study of the data, obtained by new deep-ocean profiling floats, has revealed that the thickness of the AABW off the coast has been rapidly decreasing since 2011.

This is the first study to identify changes in water masses and/or ocean circulation using deep-ocean profiling floats.

In the coastal regions near Adélie/George V Land, dense water has been formed as a result of a large amount of sea ice formation at the Mertz Glacier Polynya. The water descends into the deep ocean and forms the AABW by mixing with surrounding waters. Recently however, the mechanism of sea ice formation in the region has changed drastically due to the calving of the Mertz Glacier Tongue in 2010. It is likely that this event changed the properties of the AABW off the Adélie/George V Land coast; however, the details have yet to be clarified due to a lack of available data.

To examine changes in the AABW off the Adélie/George V Land coast, JAMSTEC’s research vessel Mirai deployed the “Deep NINJA” deep-ocean profiling float in December 2012. Dr. Kobayashi analyzed 20-months of observation data obtained by these floats along with other historical hydrographic data. He discovered that the thickness of the AABW has been decreasing by 57 m per year since 2011, which is four to five times faster than its average of 12 m per year since the 1990s.

According to Dr. Kobayashi: “Our new deep-ocean profiling float, the Deep NINJA, allowed us to examine the changes in the AABW off the Adélie/George V Land even under the sea ice during the Antarctic winter. The reduced supply of AABW could affect not only the waters surrounding the region, but also ocean circulation, material cycles, and global climates. Therefore, the long-term monitoring and analysis of changes in the AABW is important to estimate its impacts on the climate.”

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