Effect of wind on continental shelf carbon fluxes off southeast Australia: A numerical model

Abstract

A coupled physical‐biological‐chemical model is used to study the effect of upwelling‐favorable and downwelling‐favorable winds on carbon biogeochemistry on the continental shelf off the southeast Australian mainland. Along the continental shelf, from 30°S to 34°S, upwelling‐favorable winds, with the aid of bottom Ekman transport, bring dissolved‐inorganic‐carbon (DIC)‐rich slope waters onto the shelf, increasing the carbon held in shelf waters. For downwelling‐favorable winds, bottom Ekman transport still lifts slope waters onto the shelf, but the slope water transport, and therefore carbon held, is reduced compared with the upwelling scenario. Under upwelling‐favorable winds, filaments of DIC and dissolved‐inorganic‐nitrogen (DIN)‐rich water reaching the surface produce an outgassing near the site of upwelling and absorption downstream due to primary productivity. In a region of the ocean that is generally absorbing, the net effect of upwelling is a reduced absorption of atmospheric CO2 as a result of the ratio of deep DIC and DIN (12.2:1 mol C:mol N) being greater than the Redfield ratio (6.625). Carbon fluxes in the waters off the southeast Australian mainland are variable in space, with the transport of continental shelf waters to deep waters occurring mainly where alongshore currents separate from the coast and flow over the 200‐m isobath.