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- Title
Major Contribution of Reduced Upper Ocean Oxygen Mixing to Global Ocean Deoxygenation in an Earth System Model.
- Authors
Couespel, Damien; Lévy, Marina; Bopp, Laurent
- Abstract
We present a quantitative analysis of deoxygenation drivers applied to an Earth System Model and easily transposable to large model ensembles. The preindustrial ocean breathes in oxygen in polar regions and in subtropical gyres, and breathes out oxygen in the equatorial band and in subpolar gyres. Under a high‐CO2 emission scenario for the 21st century, small deviations of these large natural oxygen fluxes cause global deoxygenation. We attribute half of this trend to a decrease in oxygen solubility. The other half is explained by negative trends in subduction and respiration, which largely cancel out each other. Moreover, 75% of the subduction decrease occurs through changes in mixing across the mixed‐layer base. Our analysis also highlights strong modulations of subduction at the regional scale linked to shifts in wind patterns and associated Ekman pumping. Plain Language Summary: Oxygen in the ocean has declined over the past 50 years and is expected to further decline by 2100—a phenomenon referred to as ocean deoxygenation. This oxygen decrease may strongly impact marine habitat and enhance the production of nitrous oxide, a powerful greenhouse gas. Dissolved oxygen is transported by ocean currents or mixed from the well‐oxygenated surface to ocean depths where it is respired by marine life. Using a climate model, we find that half of ocean deoxygenation in the 21st century relates to lower oxygen solubility induced by ocean warming. In addition, we show that the rest of the decrease is caused by large changes in mixing and currents, partially compensated by lower respiration at depth. Finally, we show that most of ocean deoxygenation is due to reduced mixing and that shifts in wind patterns are modifying the oxygen supply at the local and regional scales. Key Points: O2 subduction and respiration diagnostics are used to quantify the drivers of deoxygenation at the scale of ocean basinsReduced solubility, reduced subduction, and reduced export explain 50%, 150%, and −100% of global deoxygenation, respectivelyReduced mixing explains 75% of reduced subduction, but locally the largest changes in subduction result from shifts in Ekman pumping patterns
- Subjects
OCEANIC mixing; EARTH system science; OCEAN currents; MARINE biology; MARINE habitats; OXYGEN content of seawater; EKMAN motion theory; CLIMATE change models
- Publication
Geophysical Research Letters, 2019, Vol 46, Issue 21, p12239
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2019GL084162