Salt-finger driven enhancement of upper ocean nutrient supply

Abstract

In the subtropics, estimates of upper-ocean nitrate supply by turbulent mixing have been found insufficent to balance estimated nutrient loss through organic-matter export. Most mixing-rate estimates as well as numerical turbulence closure schemes commonly employed in numerical models have, however, neglected salt-finger induced mixing. Here we examine the potential contribution of salt-finger induced mixing to nutrient fluxes. Our model results suggest that salt-fingering instabilities generate substantial nutrient fluxes (on average 0.03 mol N m-2 yr-1) which are of similar magnitude as fluxes associated with mechanically induced turbulence or with mesoscale eddies. Because salt-fingering activity depends on the proportion of temperature versus salinity effects on stratification rather than on the stability of stratification itself, its sensitivity to climate change will differ from that of "ordinary" mixing processes and needs to be considered in the context of global change. Copyright 2003 by the American Geophysical Union.