MODULATION OF BOTTOM HYPOXIA BY SUBMESOSCALE SHELF EDDIES IN THE NORTHERN GULF OF MEXICO

Seasonal bottom hypoxia in the northern Gulf of Mexico is observed to have significant variability on lateral spatial scales of 10-50 km. Numerical simulations of bottom hypoxia also suggest similar scales of variability in bottom oxygen throughout the region of shelf affected by seasonal hypoxia. The patchiness of bottom hypoxia is correlated with displacements of the pycnocline caused by the submesoscale eddy circulation. Earlier studies suggested that this variability was associated with local bathymetric features, but recent simulations suggest that the variability is caused by baroclinic instability of the Mississippi/Atchafalaya plume. Thus, the eddies and corresponding modulation of the bottom oxygen field are dynamic. There is some evidence from idealized simulations that these features migrate shoreward through interaction of the eddies with the seafloor, and associated convergent flow in the bottom boundary layer. While is it still unclear how variability in bottom oxygen will affect benthic organisms, it is important to characterize the temporal and spatial variability of the bottom oxgen for future work on this topic.