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

• Published in: Journal of geophysical research. Oceans 2013-10, Vol.118 (10), p.5504-5522
• Main Authors: Baumann, M. S., Moran, S. B., Lomas, M. W., Kelly, R. P., Bell, D. W.
• Format: Article
• Language: English
• Subjects: 234Th; Bering Sea; Carbon; Carbon dioxide; e-ratio; Earth, ocean, space; Exact sciences and technology; Exports; External geophysics; Fluxes; Geophysics; Ice; International trade; Marine; net primary production; Oceanography; Particulate organic carbon; Physics of the oceans; POC export; Primary production; Proximity; Sea ice; Shelves; Spring; Springs; Summer; Thorium; Water column
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/jgrc.20366

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, 234Th‐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 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 234Th 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 CO2 in this and other polar shelf regions. Key Points POC export and e‐ratio increase from spring to summer No direct relationship between POC export or the e‐ratio and sea‐ice proximity Off‐shelf POC transport may be an important seasonal net sink for carbon