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The extent to which polynyas can sequester atmospheric CO 2 via marine production is not known, due partly to difficulties in modeling the biological pump and undersampling of Arctic environments. These regions are known to have higher rates of primary production compared to ice-covered ones owing to open water, an ample supply of nutrients, and enough sunlight. Concurrent with sea ice recession is an increase in coastal, open water habitats known as polynyas. Since sea ice is a critical parameter controlling global climate, Arctic research has recently acquired a new mandate. Arctic sea ice is receding at a rate of several kilometers per year. These fluxes are greater than estimates of organic carbon remineralization and burial in sediments of the polynya (∼3 mmol m −2 d −1), suggesting that POC may be exported out of the area, effectively remineralized by microbial activity in the twilight zone or incorporated into biomass.
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Comparable fluxes are observed at 100 m in June, but values decrease to ∼6 mmol C m −2 d −1 at 100 m in July. Fluxes of marine POC in the polynya average ∼5 mmol C m −2 d −1 at 50 m in June 2004 and increase to ∼12 mmol C m −2 d −1 in July. The fraction of marine POC ranged from 0 to 59% in the area in June/July 2004, with highest values in the Cape Bathurst Polynya. Using a two-end-member mixing model with marine POC = −21.4‰ and terrestrial POC = −28‰ shows that terrestrial POC is most evident at the Mackenzie Shelf stations but is present throughout the region. The δ 13C values of POC in the >70- μm particles filtered in situ pumps ranged from −25.1‰ to −28‰. Deficits in the upper 100 m ranged from 3 to 59 dpm m −2 in the Cape Bathurst Polynya. In June/July 2004, the greatest 234Th deficits (0-100 m: 56-95 dpm m −2) were observed in the Mackenzie outer shelf. The 234Th fluxes were converted to marine and terrestrial POC fluxes using the POC/Th ratio on filterable particles >70 μm and δ 13C measurements to determine the fraction of marine and terrestrial POC. Water column deficits of 234Th relative to 238U in the Mackenzie Shelf, Cape Bathurst Polynya, and Amundsen Gulf were used to estimate sinking fluxes of particulate organic carbon (POC) in these areas.