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Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long‐term global warming
Author(s) -
Yamamoto A.,
AbeOuchi A.,
Shigemitsu M.,
Oka A.,
Takahashi K.,
Ohgaito R.,
Yamanaka Y.
Publication year - 2015
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2015gb005181
Subject(s) - effects of global warming on oceans , oceanography , biogeochemical cycle , deep sea , environmental science , deep ocean water , thermohaline circulation , seawater , ocean current , ocean heat content , carbon cycle , oxygen , carbon dioxide , global warming , climatology , geology , climate change , chemistry , ecosystem , ecology , biology , organic chemistry , environmental chemistry
Abstract Global warming is expected to decrease ocean oxygen concentrations by less solubility of surface ocean and change in ocean circulation. The associated expansion of the oxygen minimum zone would have adverse impacts on marine organisms and ocean biogeochemical cycles. Oxygen reduction is expected to persist for a thousand years or more, even after atmospheric carbon dioxide stops rising. However, long‐term changes in ocean oxygen and circulation are still unclear. Here we simulate multimillennium changes in ocean circulation and oxygen under doubling and quadrupling of atmospheric carbon dioxide, using a fully coupled atmosphere‐ocean general circulation model and an offline biogeochemical model. In the first 500 years, global oxygen concentration decreases, consistent with previous studies. Thereafter, however, the oxygen concentration in the deep ocean globally recovers and overshoots at the end of the simulations, despite surface oxygen decrease and weaker Atlantic meridional overturning circulation. This is because, after the initial cessation, the recovery and overshooting of deep ocean convection in the Weddell Sea enhance ventilation and supply oxygen‐rich surface waters to deep ocean. Another contributor to deep ocean oxygenation is seawater warming, which reduces the export production and shifts the organic matter remineralization to the upper water column. Our results indicate that the change in ocean circulation in the Southern Ocean potentially drives millennial‐scale oxygenation in deep ocean, which is opposite to the centennial‐scale global oxygen reduction and general expectation.