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General Session 2: Marine & estuarine biogeochemistry |
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Pause in the decline of oxygen in the tropical Pacific Ocean's oxygen minimum
Tuesday 10th @ 1130-1150
Conference Hall
Xiujun Wang* , Beijing Normal University
Dongxiao Zhang, University of Washington
Raghu Murtugudde, University of Maryland
Presenter Email: xwang@bnu.edu.cn
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| The Oxygen-Minimum-Zone (OMZ), often seen below 200 m, is a profound feature in the world ocean. There has been evidence of OMZ expansion with a declining trend in dissolved oxygen over the past few decades in the tropical oceans. Recently, one hypothesis was proposed that there would be shrinkage of the OMZs and/or an increase in the mid-depth oxygen concentration in the tropical Pacific following the recent strengthening of wind-driven ocean transport and upwelling. To date, there is a lack of quantitative analyses of sources and sinks of oxygen for the tropical Pacific Ocean so that the changing trend of mid-depth oxygen and underlying mechanisms are not well understood. The objectives of this study were: to provide quantitative analyses of relative strength of oxygen supply and removal in the tropical Pacific and to test the hypothesis that the OMZ would contract in association with the recent resumption of trade winds. We employed a fully coupled three-dimensional physical-biogeochemical model that can reproduce the observed magnitude and spatial pattern of dissolved oxygen, including the vertical and zonal distributions, and the meridional asymmetry of dissolved oxygen distribution in the tropical Pacific. Model experiment was conducted to evaluate the previously proposed mechanisms (i.e., reduced physical supply and enhanced consumption) for the decline of mid-depth dissolved oxygen in the tropical Pacific. Our findings indicate that the changing trend was not a result of any single mechanisms. Our analyses demonstrates that the rate of consumption was greater than the rate of supply prior to the year ~2000 in the tropical Pacific, which led to a decreasing trend in the mid-depth dissolved oxygen; on the other hand, oxygen supply exceeded oxygen consumption post ~2000 only in some parts of the basin. Overall, the recent strengthening of wind-driven ocean transport and upwelling did not lead to shrinkage of the OMZs or an increase in the mid-depth dissolved oxygen, but a pause in the decline of dissolved oxygen in the tropical Pacific’s OMZ. The results will be placed in the context of natural variability and the trends. |
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