| Summary: | The Chukchi Sea, a shallow sea-ice covered coastal sea adjacent to the Arctic Ocean, exhibits an intense bloom of phytoplankton each year due to the exposure of nutrient-laden surface waters during the brief summertime retreat and melting of sea-ice. The impact of phytoplankton production and other factors on the seasonal dynamics of carbon and air-sea CO 2 fluxes were investigated during two survey cruises (5 May–15 June 2002, and 17 July–26 August 2002), as part of the Western Arctic Shelf-Basins-Interactions (SBI) project. In springtime, most of the Chukchi Sea was sea-ice covered (>95%) and remnant winter water was present across the shelf. Surface layer seawater partial pressure of CO 2 (pCO 2 ) ranged from ~200–320 µatm, indicative of undersaturation with respect to atmospheric pCO2, although sea-ice cover kept rates of air-to-sea CO 2 flux generally low (<1 mmoles CO 2 m 2 d -1 ). By summertime, after sea-ice retreat, seawater pCO 2 contents had decreased to very low values (<80–220 µatm) in response to high rates of localized primary and net community production (NCP) and biological uptake of dissolved inorganic carbon (DIC). In the seasonally sea-ice free regions of the Chukchi Sea shelf, rates of air-to-sea CO 2 fluxes, determined using the quadratic wind speed-transfer velocity relationships of Wanninkhof (1992), were high, ranging from ~30–90 mmoles CO 2 m -2 d -1 . In regions of the Chukchi Sea slope (and western Beaufort Sea shelf and Arctic Ocean basin) where sea-ice cover remained high (>80%), air-to-sea CO 2 fluxes remained generally low (<2 mmoles CO 2 m -2 d -1 ). Seasonal (i.e., May to September) and annual net air-to-sea CO 2 fluxes from the Chukchi Sea shelf were estimated at ~27 ± 7 Tg C yr -1 , and 38 ± 7 Tg C yr -1 , respectively. The Chukchi Sea represents the largest oceanic CO 2 sink in the marginal coastal seas adjacent to the Arctic Ocean. An active continental shelf pump of carbon, driven by the northward transport of nutrient-rich water of Pacific Ocean origin, high ...
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