Abstract
In the tropical Pacific, weak ventilation and intense microbial
respiration at depth give rise to a low dissolved oxygen (O2)
environment that is thought to be ventilated primarily by the equatorial
current system (ECS). The role of mesoscale eddies and diapycnal mixing
as potential pathways of O2 supply in this region, however, remains
poorly known due to sparse observations and coarse model resolution.
Using an eddy resolving simulation of ocean circulation and
biogeochemistry, we assess the contribution of these processes to the O2
budget balance and find that turbulent mixing of O2 and its modulation
by mesoscale eddies contribute substantially to the replenishment of O2
in the upper equatorial Pacific thermocline, complementing the advective
supply of O2 by the ECS and meridional circulation at depth. These
transport processes are strongly sensitive to seasonal forcing by the
wind, with elevated mixing of O2 into the upper thermocline during
summer and fall when the vertical shear of the lateral flow and eddy
kinetic energy are intensified. The tight link between eddy activity and
the downward mixing of O2 arises from the modulation of equatorial
turbulence by Tropical Instability Waves via their eddy impacts on the
vertical shear. This interaction of ocean processes across scales
sustains a local pathway of O2 delivery into the equatorial Pacific
interior and highlights the need for adequate observations and model
representation of turbulent mixing and mesoscale processes for
understanding and predicting the fate of the tropical Pacific O2 content
in a warmer and more stratified ocean.