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

• Published in: Journal of Geophysical Research
• Main Authors: Martz, TR, DeGrandpre, MD, Strutton, PG, McGillis, WR, Drennan, WM
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Geophysical Union 2009
• Subjects: Earth Sciences; Oceanography; Biological oceanography; Labrador Sea
• Online Access: https://doi.org/10.1029/2008JC005060; http://ecite.utas.edu.au/80210

We report depth-resolved in situ time series of the partial pressure of CO 2 ( p CO 2 ) andother carbon-related parameters spanning the development and decline of a high-latitudephytoplankton bloom. A suite of sensors was deployed on a mooring in the LabradorSea from June to August 2004. The study became quasi-Lagrangian when the mooringbroke free in late June. Measured parameters included p CO 2 , chlorophyll a fluorescence, beam c, optical backscatter, and photosynthetically active radiation.During the bloom, the p CO 2 was drawn down from 330 to 260 μatm, corresponding to a70 μmol kg -1 decrease of dissolved inorganic carbon (DIC). One-dimensional model resultssuggest that the observed drawdown was primarily driven by local processes andcontributions from horizontal advection were minimal. A mass balance using the DIC andparticulate organic carbon found that 47 mmol C m -2 d -1 of DIC was assimilated intobiomass. The bloom biomass was not remineralized in the mixed layer but was rapidlyexported below 35 m within 15 days of the bloom. As a consequence, the large air-sea p CO 2 gradient persisted, and approximately 30% of the DIC was regained through air-seaexchange 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 p CO 2 prior to the onsetof deep convective mixing.