CO₂ fluxes across the air‐sea interface in the southeastern Beaufort Sea: Ice‐free period

Abstract

[1] Surface mixed layer CO 2 fugacities (fCO 2 -sw) calculated from carbonate system parameters in the southeastern Beaufort Sea during the ice-free period ranged from 240 to 350 matm in fall 2003 and from 175 to 515 matm in summer 2004. The surface mixed layer remains mostly undersaturated with respect to atmospheric CO 2 (378 matm) and, therefore, acts as a potential CO 2 sink throughout this period. Air-sea CO 2 fluxes (FCO 2 ) were first computed assuming ice-free conditions and ranged from −32.4 to +8.6 mmol m on the western Mackenzie Shelf to +8.6 mmol m −2 d −1 at Cape Bathurst; the variability being ascribed to competing effects of vertical mixing, temperature variations, and possibly biological production. On average, a net sink of −2.3 ± 3.5 mmol m −2 d −1 was estimated for the ice-free period over the study area. Nevertheless, the FCO 2 displays strong variability due to ice coverage, freshwater input, and upwelling events. The potential responses (direction and intensity of potential feedbacks) of the carbon cycle in the study area to a changing Arctic climate are discussed.

Seasonal variability of the inorganic carbon system in the Amundsen Gulf region of the southeastern Beaufort Sea

“…The surface waters of Amundsen Gulf were weakly undersaturated with respect to atmospheric CO 2 throughout the year. Hence, during the open-water months, the region acted as a moderate sink for atmospheric CO 2 , as reported by Mucci et al (2010), but these inputs made only a minor contribution to the monthly changes in surface DIC. Biological processes thus made up the balance of the observed monthly changes in surface DIC and TA.…”

“…Carbon losses due to burial in the sediments, at a depth of 350-380 m, thus account for a small percentage of primary production, and were assumed negligible over the annual time scale of interest (Mucci et al 2008). Furthermore, it has been shown that sedimentation rates in Amundsen Gulf are very low (Macdonald et al 1998;Richerol et al 2008).…”

“…The hourly fluxes were averaged spatially over the area of the surface box and integrated over 1 month, representing the monthly change in DIC due to the air-sea exchange of CO 2 . The CO 2 fluxes were computed assuming ice-free conditions and then scaled using a multiplier equal to 100% minus the percentage ice cover following Bates (2006) and Mucci et al (2010; see Table 1). This method assumes that sea-ice is an effective barrier to air-sea gas exchange, and that the resulting air-sea fluxes of CO 2 are a linear function of sea-ice cover.…”

“…Most observational studies have been limited to the summer and autumn seasons, when reduced ice-cover allows access Mathis et al 2007;Mucci et al 2010). Observational data of the inorganic carbon system in the Arctic, particularly outside of the summer and autumn seasons are, therefore, sparse.…”

Role of sea ice in global biogeochemical cycles: emerging views and challenges

“…However, recent findings point to significant CO 2 fluxes through sea ice [Delille, 2006;Nomura et al, 2010]. At this stage, observations suggest that the sea ice zone could be a source of atmospheric CO 2 in winter [Miller et al, 2011b], and a sink in summer and fall [Else et al, 2008;Mucci et al, 2010], with a transition period in between Nomura et al, 2010], and a net uptake from the sea ice zone on an annual basis [Rysgaard et al, 2011].…”