ENHANCED ABYSSAL MIXING IN THE EQUATORIAL PACIFIC ASSOCIATED WITH NON-TRADITIONAL EFFECTS

Abstract:

Recent theoretical work have shown that, when the full Coriolis force and the so-called non-traditional effects are taken into account, the reflection of Equatorially Trapped Waves (ETWs) off the seafloor generates strong vertical inertial shear that result in bottom-intensified mixing at the inertial latitude of the ETW through the mechanism of critical reflection. It has been estimated that this process can result in order 10 Sv of diapycnal upwelling, and thus could play an important role in closing the Abyssal Meridional Overturning Circulation (AMOC). However, these results have been derived under an idealized configuration with a background state at rest, a flat seafloor, and a monochromatic ETW field. To test the theory in a flow that is more representative of the ocean, we use realistic numerical simulations of the Equatorial Pacific where the traditional approximation of neglecting the horizontal component of the Coriolis parameter has been relaxed (i.e. we use a quasi-hydrostatic version of the model). Our simulations are nested into a Pacific-wide hydrostatic parent solution forced with climatological forcing and realistic bathymetry, resulting in an ETW field and a deep mean circulation consistent with observations. Using these realistic simulations, we observe enhanced abyssal mixing even over smooth topography, in the quasi-hydrostatic case. The mixing is associated with strong inertial vertical shear as predicted by the theory. The spatio-temporal properties of the mixing will be presented and its implications on vertical transport of water masses and the closure of the AMOC will be discussed.