Air-sea CO₂ fluxes and the continental shelf pump of carbon in the Chukchi Sea adjacent to the Arctic Ocean

Bates, Nicholas R. (2006) Air-sea CO₂ fluxes and the continental shelf pump of carbon in the Chukchi Sea adjacent to the Arctic Ocean. Journal of Geophysical Research: Oceans, 111 (C10), C10013. (doi:10.1029/2005JC003083).

Abstract

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 CO₂ 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 CO₂ (pCO₂) ranged from ~200–320 µatm, indicative of undersaturation with respect to atmospheric pCO2, although sea-ice cover kept rates of air-to-sea CO₂ flux generally low (<1 mmoles CO₂ m² d^-1). By summertime, after sea-ice retreat, seawater pCO₂ 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 CO₂ fluxes, determined using the quadratic wind speed-transfer velocity relationships of Wanninkhof (1992), were high, ranging from ~30–90 mmoles CO₂ 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 CO₂ fluxes remained generally low (<2 mmoles CO₂ m^-2 d^-1). Seasonal (i.e., May to September) and annual net air-to-sea CO₂ 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 CO₂ 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 rates of primary and net community production during the sea-ice free period, and lateral export of organic carbon, maintains the Chukchi Sea shelf and slope as a perennial ocean CO₂ sink.

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