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Projected Centennial Oxygen Trends and Their Attribution to Distinct Ocean Climate Forcings
Author(s) -
Takano Yohei,
Ito Takamitsu,
Deutsch Curtis
Publication year - 2018
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 - 10.1029/2018gb005939
Subject(s) - thermocline , climatology , environmental science , biogeochemistry , ocean heat content , southern hemisphere , oceanography , climate change , subarctic climate , atmospheric sciences , climate model , centennial , thermohaline circulation , geology , geography , archaeology
We explore centennial changes in tropical Pacific oxygen (O 2 ) using numerical models to illustrate the dominant patterns and mechanisms under centennial climate change. Future projections from state‐of‐the‐art Earth System Models exhibit significant model to model differences, but decreased solubility and weakened ventilation together deplete thermocline O 2 in middle to high latitudes. In contrast, the tropical thermocline O 2 undergoes much smaller changes or even a slight increase. A suite of sensitivity experiments using a coarse resolution ocean circulation and biogeochemistry model show that ocean warming is the leading cause of global deoxygenation in the thermocline across all latitudes with secondary contributions from changes in hydrological cycles and wind stress modulating regional changes in O 2 . The small O 2 changes in the tropical Pacific thermocline reflect near‐complete compensation between the solubility decrease due to warming and reduction in apparent oxygen utilization (AOU). We further quantified the changes in AOU due to contributions from changes in water mass age and biological remineralization from the sensitivity experiments. The two effects almost equally contribute to the reduction of AOU in the tropical Pacific thermocline (43% for physical circulations and 57% for biology). Our results suggest that better understanding of water mass changes in the tropical oceans is key to improving projections and reducing the uncertainties of future O 2 changes.