Understanding why the volume of suboxic waters does not increase over centuries of global warming in an Earth System Model

摘要

Global warming is expected to reduce oxygen solubility and vertical exchangein the ocean, changes which would be expected to result in an increase inthe volume of hypoxic waters. A simulation made with a full Earth Systemmodel with dynamical atmosphere, ocean, sea ice and biogeochemical cycling(the Geophysical Fluid Dynamics Laboratory's Earth System Model 2.1)shows that this holds true if the condition for hypoxia is set relativelyhigh. However, the volume of the most hypoxic (i.e., suboxic) waters does not increase underglobal warming, as these waters actually become more oxygenated. We showthat the rise in dissolved oxygen in the tropical Pacific is associated with a drop in ventilation time. Aterm-by-term analysis within the least oxygenated waters shows an increasedsupply of dissolved oxygen due to lateral diffusion compensating an increase inremineralization within these highly hypoxic waters. This lateral diffusiveflux is the result of an increase of ventilation along the Chilean coast, asa drying of the region under global warming opens up a region of wintertimeconvection in our model. The results highlight the potential sensitivity ofsuboxic waters to changes in subtropical ventilation as well as the importanceof constraining lateral eddy transport of dissolved oxygen in such waters.