Air‐Sea CO2 Exchange in the Ross Sea, Antarctica

Abstract

AbstractAlthough the Ross Sea is one of the most productive regions in Antarctica, it is not clear to what extent this region is an atmospheric CO2 sink. We calculate instantaneous CO2 flux rates with in situ pCO2 and wind speed data from 20 cruises in the Ross Sea. In addition, we estimate annual CO2 fluxes into the Ross Sea with nutrient budgets from a late summer cruise. We find that the Ross Sea is a lesser atmospheric CO2 sink (–7.5 ± 0.5 Tg C yr−1, −1.3 ± 0.1 mol C m−2 yr−1) than previously reported (–13 Tg C yr−1, −1.7 to −4.2 mol C m−2 yr−1). One exception is Terra Nova Bay (TNB) in the western Ross Sea, with CO2 flux rates (–4.8 ± 0.3 mol C m−2, January–March) that are 3–4 times greater than the Ross Sea mean. The majority of the CO2 flux into TNB occurs during the late summer with instantaneous CO2 flux rates up to −246 mmol C m−2 d−1. These extraordinary CO2 flux rates are caused by the unique coupling of strong katabatic winds and low surface pCO2 values. Although strong katabatic winds deepen the mixed layer and entrain CO2‐rich water from below, late season net community productivity maintains low surface water pCO2 levels. While TNB only covers ∼1% (3,600 km2) of the Ross Sea continental shelf, extraordinary air‐to‐sea CO2 fluxes during the late summer may be regular features in many of the major sea ice production polynyas (148,000 km2 combined), including Antarctic Bottom Water formation regions.