Air-sea CO₂ fluxes on the Bering Sea shelf

Abstract. There have been few previous studies of surface seawater CO₂ partial pressure (pCO₂) variability and air-sea CO₂ gas exchange rates for the Bering Sea shelf. In 2008, spring and summertime observations were collected in the Bering Sea shelf as part of the Bering Sea Ecological Study (BEST). Our results indicate that the Bering Sea shelf was close to neutral in terms of CO₂ sink-source status in springtime due to relatively small air-sea CO₂ gradients (i.e., ΔpCO₂ and sea-ice cover. However, by summertime, very low seawater pCO₂ values were observed and much of the Bering Sea shelf became strongly undersaturated with respect to atmospheric CO₂ concentrations. Thus the Bering Sea shelf transitions seasonally from mostly neutral conditions to a strong oceanic sink for atmospheric CO₂ particularly in the "green belt" region of the Bering Sea where there are high rates of phytoplankton primary production (PP)and net community production (NCP). Ocean biological processes dominate the seasonal drawdown of seawater pCO₂ for large areas of the Bering Sea shelf, with the effect partly countered by seasonal warming. In small areas of the Bering Sea shelf south of the Pribilof Islands and in the SE Bering Sea, seasonal warming is the dominant influence on seawater pCO₂, shifting localized areas of the shelf from minor/neutral CO₂ sink status to neutral/minor CO₂ source status, in contrast to much of the Bering Sea shelf. Overall, we compute that the Bering Sea shelf CO₂ sink in 2008 was 157 ± 35 Tg C yr⁻¹ (Tg = 10¹² g C) and thus a strong sink for CO₂.