High-resolution, basin-scale simulations reveal the impact of
intermediate zonal jets on the Atlantic oxygen minimum zones
Abstract
Intermediate, eastward zonal jets are important conduits of oxygen
across the Atlantic Ocean as they connect the oxygen-rich western
boundary of the basin with the oxygen minimum zones (OMZs) on the
eastern boundary. These jets are not well represented in climate models
because the relatively low horizontal resolution of these models usually
yields excessive viscosity. We use two physical-biogeochemical model
configurations of the Tropical Atlantic Ocean at different resolutions
to show that the increase in resolution results, on average, in more
robust intermediate, eastward zonal jets. Larger viscosity in the low
resolution runs inhibits strong eastward jets at depth. The upper ocean
circulation is not significantly affected by the difference in
resolution. This causes westward jets in the upper 300 m to advect low
oxygen waters further west than in the climatology, thus distorting the
vertical structure of the OMZ by making them thinner and wider.
Potential vorticity analysis confirms that surface westward jets are
associated homogenized PV contours while eastward jets are associated
with regions of potential vorticity gradients. Eastward jets constrain
the westward expansion of the OMZs by supplying oxygen to the western
edge of the OMZs. Model diagnostics show that advection dominates oxygen
transport in the OMZ core, with increased transport in the
high-resolution run. Basin-scale, high-resolution runs are necessary to
simulate the transfer of energy across scales that results in robust
zonal jets as well as their impact on the ocean biogeochemistry. This
provides a pathway to disentangle natural and antrhopogenic causes of
ocean deoxygenation.