Fluxes of carbon and nutrients to the Iceland Sea surface layer and inferred primary productivity and stoichiometry

This study evaluates long-term mean fluxes of carbon and nutrients to the upper 100m of the Iceland Sea. The study utilises hydro-chemical data from the Iceland Sea time series station (68.00 degrees N, 12.67 degrees W), for the years between 1993 and 2006. By comparing data of dissolved inorganic carbon (DIC) and nutrients in the surface layer (upper 100 m), and a sub-surface layer (100-200 m), we calculate monthly deficits in the surface, and use these to deduce the long-term mean surface layer fluxes that affect the deficits: vertical mixing, horizontal advection, air-sea exchange, and biological activity. The deficits show a clear seasonality with a minimum in winter, when the mixed layer is at the deepest, and a maximum in early autumn, when biological uptake has removed much of the nutrients. The annual vertical fluxes of DIC and nitrate amounts to 2.9 +/- 0.5 and 0.45 +/- 0.09 mol m(-2) yr(-1), respectively, and the annual air-sea uptake of atmospheric CO2 is 4.4 +/- 1.1 mol C m(-2) yr(-1). The biologically driven changes in DIC during the year relates to net community production (NCP), and the net annual NCP corresponds to export production, and is here calculated as 7.3 +/- 1.0 mol C m(-2) yr(-1). The typical, median C : N ratio during the period of net community uptake is 9.0, and clearly higher than the Redfield ratio, but is varying during the season.