Air‐Sea CO₂ Exchange in the Ross Sea, Antarctica

Although the Ross Sea is one of the most productive regions in Antarctica, it is not clear to what extent this region is an atmospheric CO 2 sink. We calculate instantaneous CO 2 flux rates with in situ p CO 2 and wind speed data from 20 cruises in the Ross Sea. In addition, we estimate annual CO 2 fluxes into the Ross Sea with nutrient budgets from a late summer cruise. We find that the Ross Sea is a lesser atmospheric CO 2 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 CO 2 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 CO 2 flux into TNB occurs during the late summer with instantaneous CO 2 flux rates up to −246 mmol C m −2 d −1 . These extraordinary CO 2 flux rates are caused by the unique coupling of strong katabatic winds and low surface p CO 2 values. Although strong katabatic winds deepen the mixed layer and entrain CO 2 ‐rich water from below, late season net community productivity maintains low surface water p CO 2 levels. While TNB only covers ∼1% (3,600 km 2 ) of the Ross Sea continental shelf, extraordinary air‐to‐sea CO 2 fluxes during the late summer may be regular features in many of the major sea ice production polynyas (148,000 km 2 combined), including Antarctic Bottom Water formation regions.