OS033-05
Mesoscale Controls on the Equatorial Pacific Oxygen Balance: A Model Study

Friday, 11 December 2020: 16:32
Virtual
Yassir Eddebbar, Scripps Institution of Oceanography, La Jolla, CA, United States, Aneesh Subramanian, University of Colorado Boulder, Boulder, CO, United States, Daniel B Whitt, NCAR, CO, United States, Matthew C Long, National Center for Atm Res, Boulder, CO, United States, Ariane Verdy, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, United States, Matthew R Mazloff, SIO, La Jolla, CA, United States and Mark A Merrifield, University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States
Recorded Presentation
Abstract:
The tropical Pacific is home to two of the world’s largest oxygen minimum zones (OMZs). These OMZs result from weak ventilation and microbial respiration at depth, and exert major controls on marine ecosystem habitable space, nutrient cycling, and nitrous oxide production. Recent synthesis of global observations reports a decline in the world ocean dissolved oxygen ([O2]) content since 1960, with significant contributions from the equatorial Pacific where [O2] loss is exhibited as an expansion of the OMZs. Attribution and mechanistic understanding of these regional trends, however, remain challenged by large natural variability and poor understanding of processes governing the [O2] budget in this region. Using an eddy-resolving configuration of the Community Earth System Model (CESM), we explore the role of mesoscale circulation on the 3D structure and variability of [O2] in the upper equatorial Pacific, with a particular focus on Tropical Instability Vortices (TIVs). The simulated generation and westward translation of TIVs from boreal summer through winter lead to a strongly seasonal oxygenation of the upper northern equatorial Pacific (2º-8ºN), with notable impacts on the depth of the equatorward boundary of the OMZ west of 120ºW. TIV effects on the equatorial Pacific oxygen balance are dominated by lateral and vertical eddy advective and mixing processes, while indirect effects on [O2] consumption play minor roles. Lagrangian analysis reveals complex kinetics governing the TIV advective effects, including contributions from eddy trapping, eddy stirring, and vortex-induced subduction and upwelling. Near the equator, TIV-induced vertical mixing of subsurface [O2]-undersaturated waters lead to vigorous air-sea flux of [O2], and is tightly linked to TIV variations in current shear and stratification. These mesoscale effects will be discussed in the context of basin scale OMZ dynamics and model biases, and present new opportunities for future process studies and autonomous biogeochemical sensing under the new Tropical Pacific Observing System.
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