Seasonal decoupling of particulate organic carbon export and net primary production in relation to sea‐ice at the shelf break of the eastern Bering Sea: Implications for off‐shelf carbon export

Particulate organic carbon (POC) export fluxes and net primary production (NPP) rates are used to assess seasonal patterns in the export ratio ( e ‐ratio = POC export/NPP) in relation to proximity of the sea‐ice edge near the shelf break of the eastern Bering Sea during 2008–2010. POC fluxes were relatively low in April (4.6 ± 1.6, trap, and 5.7 ± 4.3 mmol C m −2 d −1 , 234 Th‐derived) and increased in May–early June (19.9 ± 13.3 and 17.0 ± 8.8 mmol C m −2 d −1 ). POC export reached a maximum in mid‐June–mid‐July (30.0 ± 12.6 and 48.1 ± 17.4 in 2009; 33.1 ± 27.6 and 57.0 ± 68.4 mmol C m −2 d −1 in 2010) and decreased by late July (13.1 ± 4.7 and 14.1 ± 8.0 mmol C m −2 d −1 ). NPP rates were relatively high and export fluxes low near the ice‐edge in spring leading to e ‐ratios <0.25. In early summer, POC export exceeded NPP at individual stations and resulted in e ‐ratios >1, which is attributed to a temporal decoupling, or offset, of spring NPP and export during summer. While these observations reveal a seasonal progression in POC export and the e ‐ratio, there is no direct relationship to sea‐ice proximity. Furthermore, based on a water column‐sediment 234 Th budget, the off‐shelf export of POC during spring‐summer is estimated to be 24 ± 35 mmol C m −2 d −1 , which represents an off‐shelf e ‐ratio of 0.07 and 0.21 for contemporaneous seasonally averaged daily NPP and 0.17 and 0.52 for historical monthly averaged daily NPP. An implication is that off‐shelf POC transport may represent a seasonal net sink for CO 2 in this and other polar shelf regions.