Sea surface pCO(2) and carbon export during the Labrador Sea spring-summer bloom: An in situ mass balance approach

Martz, TR, DeGrandpre MD, Strutton PG, McGillis WR, Drennan WM.  2009.  Sea surface pCO(2) and carbon export during the Labrador Sea spring-summer bloom: An in situ mass balance approach. Journal of Geophysical Research-Oceans. 114

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20-degrees-w, 47-degrees-n, assemblages, dissolved organic-carbon, iron fertilization, marine-phytoplankton, natural, north-atlantic ocean, photosynthesis, phytoplankton bloom, southern-ocean


We report depth-resolved in situ time series of the partial pressure of CO(2) (pCO(2)) and other carbon-related parameters spanning the development and decline of a high-latitude phytoplankton bloom. A suite of sensors was deployed on a mooring in the Labrador Sea from June to August 2004. The study became quasi-Lagrangian when the mooring broke free in late June. Measured parameters included pCO(2), chlorophyll a fluorescence, beam c, optical backscatter, and photosynthetically active radiation. During the bloom, the pCO(2) was drawn down from 330 to 260 mu atm, corresponding to a 70 mu mol kg(-1) decrease of dissolved inorganic carbon (DIC). One-dimensional model results suggest that the observed drawdown was primarily driven by local processes and contributions from horizontal advection were minimal. A mass balance using the DIC and particulate organic carbon found that 47 mmol C m(-2) d(-1) of DIC was assimilated into biomass. The bloom biomass was not remineralized in the mixed layer but was rapidly exported below 35 m within 15 days of the bloom. As a consequence, the large air-sea pCO(2) gradient persisted, and approximately 30% of the DIC was regained through air-sea exchange by the end of the study. It is likely that all of the exported organic matter, corresponding to 5.4 +/- 1.9 Tg of carbon, was replaced by atmospheric CO(2) prior to the onset of deep convective mixing.






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