Euphotic Zone Residence Time of Antarctic Bottom Water

Abstract

Antarctic Bottom Water (AABW) transports surface nutrients deep into the ocean, sequestering them for centuries. Enhancing its biological carbon fixation could augment carbon sinks and reduce atmospheric CO2. Yet, it is uncertain if AABW receives enough light for significant photosynthesis before subducting. Using Lagrangian particle tracking in an ocean sea-ice model, we found: (a) 70% (66%–73%, depending on euphotic zone (Zeu) criteria) nutrient rich circumpolar deep water never enters the Zeu before becoming AABW. This percentage varies from 70% to 91%, depending on the mixed layer (ML) parameterization adjustments; (b) The remaining particles in the euphotic zone have 39 (34–49, depending on Zeu criteria) days average residence time. The time is not sensitive to ML parameterization strength but turning it off doubles the time; and (c) AABW is mainly exposed to enough light on the Antarctic continental shelf during spring and summer. We conclude that the potential of biotic carbon sequestration in AABW is highly limited by light energy.