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S-9. Climate forced variability of ocean oxygen minimum zones
Curtis Deutsch1, Holger Brix1, Taka Ito2, Hartmut Frenzel1, LuAnne Thompson3
1UCLA, Department of Atmospheric and Oceanic Science
2Colorado State University, Department of Atmospheric Science
3University of Washington, School of Oceanography
Oxygen is a critical constraint on the respiratory environment in marine ecosystems. As the concentration of O2 in seawater falls to hypoxic levels, the habitability for aerobic organisms decreases rapidly. We show that the spatial extent of hypoxia is intrinsically sensitive to small changes in the ocean’s O2 content, and that this sensitivity reaches a maximum at suboxic concentrations where anaerobic metabolisms predominate. In model-based reconstructions of historical oxygen changes, the volume of suboxic zones in the Pacific Ocean, where 95% of these waters reside, varies by over two-fold on interannual to decadal time scales. Small changes in the depth of the tropical and subtropical thermocline are the primary cause of this variability because thermocline depth has a multiplicative effect on the export of organic matter from surface waters and the fraction of it that is respired within the uplifted waters. Interactions between the suboxic volume and respiratory oxidant demand are predicted to cause even larger fluctuations in the rate of nitrate lost via denitrification, creating a link between decadal climate fluctuations and the nitrogen limitation of marine photosynthesis.