Ocean Deoxygenation Conference | Kiel 2018

Climate projections with Earth System Models (ESM) suggest that strong deoxygenation is projected to occur by the end of the 21st century in the temperate gyres of the North Pacific and North Atlantic. This deoxygenation trend is the consequence of a balance between 1) reduced oxygen solubility associated with warmer temperatures 2) reduced ventilation, and 3) is partly counter-balanced by reduced oxygen consumption at subsurface associated with reduced photosynthesis at the surface. These three processes, solubility, ventilation and productivity/respiration are known to be affected by physical processes occurring at meso and submesoscale which are not properly accounted for in ESM.
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In order to examine how our current projections of deoxygenation may be biased by the lack of horizontal resolution of current ESM, we carry a model study in which an idealized configuration of the temperate North Atlantic/Pacific gyres is run for several decades at three different horizontal resolutions : 100km, 12km and 4km. Two scenarios are examined : a preindustrial scenario, with a seasonally repeating atmospheric forcing, and a climate change scenario where a constant temperature trend is added to the previous forcing. The physical component of the model is NEMO, and the biogeochemical component is LOBSTER.
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Our idealized model is able to reproduce the deoxygenation trend projected by ESM with a similar amplitude. We find lower levels of deoxygenation with increasing model resolution despite lower productivity/respiration. We interpret the results by examining the trends in the oxygen equation.