The Mechanism for Antarctic Intermediate Water Renewal in a World Ocean Model

Abstract

Realistic representation of the low-salinity tongue of Antarctic Intermediate Water (AAIW) has been achieved in a coarse-resolution ocean general circulation model. The authors find that this water mass is not generated by direct subduction of surface water near the polar front. Instead, the renewal process is concentrated in the southeast Pacific Ocean off southern Chile. The outflow of the East Australian Current progressively cools (by heat loss to the atmosphere) and freshens (by assimilation of polar water, carried north by the surface Ekman drift) during its slow movement across the South Pacific toward the AAIW formation zone. Further, deep, warm advection near Chile enables more convective overturn, resulting in very deep mixed layers from which AAIW is fed into the South Pacific and also into the Malvinas Current. Along with this isolated region of AAIW renewal, the model relies on alongisopycnal mixing of fresh surface water from the polar front to capture a realistic circumpolar tongue of low salinity water at 1000-m depth.