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Carbon exchange between a shelf sea and the ocean: The Hebrides Shelf, west of Scotland
Author(s) -
Painter Stuart C.,
Hartman Susan E.,
Kivimäe Caroline,
Salt Lesley A.,
Clargo Nicola M.,
Bozec Yann,
Daniels Chris J.,
Jones Sam C.,
Hemsley Victoria S.,
Munns Lucie R.,
Allen Stephanie R.
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2015jc011599
Subject(s) - flux (metallurgy) , oceanography , downwelling , total organic carbon , dissolved organic carbon , particulates , particulate organic carbon , carbon fibers , ekman transport , environmental science , atmospheric sciences , geology , upwelling , chemistry , phytoplankton , environmental chemistry , nutrient , materials science , organic chemistry , composite number , composite material
Global mass balance calculations indicate the majority of particulate organic carbon (POC) exported from shelf seas is transferred via downslope exchange processes. Here we demonstrate the downslope flux of POC from the Hebrides Shelf is approximately 3‐ to 5‐fold larger per unit length/area than the global mean. To reach this conclusion, we quantified the offshore transport of particulate and dissolved carbon fractions via the “Ekman Drain,” a strong downwelling feature of the NW European Shelf circulation, and subsequently compared these fluxes to simultaneous regional air‐sea CO 2 fluxes and onshore wind‐driven Ekman fluxes to constrain the carbon dynamics of this shelf. Along the shelf break, we estimate a mean offshelf total carbon (dissolved + particulate) flux of 4.2 tonnes C m −1 d −1 compared to an onshelf flux of 4.5 tonnes C m −1 d −1 . Organic carbon represented 3.3% of the onshelf carbon flux but 6.4% of the offshelf flux indicating net organic carbon export. Dissolved organic carbon represented 95% and POC 5% of the exported organic carbon pool. When scaled along the shelf break the total offshelf POC flux (0.007 Tg C d −1 ) was found to be 3 times larger than the regional air‐sea CO 2 ingassing flux (0.0021 Tg C d −1 ), an order of magnitude larger than the particulate inorganic carbon flux (0.0003 Tg C d −1 ) but far smaller than the DIC (2.03 Tg C d −1 ) or DOC (0.13 Tg C d −1 ) fluxes. Significant spatial heterogeneity in the Ekman drain transport confirms that offshelf carbon fluxes via this mechanism are also spatially heterogeneous.