Seasonal cycle of O₂ and pCO₂ in the central Labrador Sea: Atmospheric, biological, and physical implications

We present full 2004-2005 seasonal cycles of CO₂ partial pressure (pCO₂) and dissolved oxygen (O₂) in surface waters at a time series site in the central Labrador Sea (56.5°N, 52.6°W) and use these data to calculate annual net air-sea fluxes of CO₂ and O₂ as well as atmospheric potential oxygen (APO). The region is characterized by a net CO₂ Sink (2.7 ± 0.8 mol CO₂ m^-2 yr^-1) that is mediated to a major extent by biological carbon drawdown during spring/summer. During wintertime, surface waters approach equilibrium with atmospheric CO₂. Oxygen changes from marked undersaturation of about 6% during wintertime to strong supersaturation by up to 10% during the spring/summer bloom. Overall, the central Labrador Sea acts as an O₂ Sink of 10.0 ± 3.1 mol m^-2 yr^-1. The combined CO₂ and O₂ sink functions give rise to a sizable APO flux of 13.0 ± 4.0 mol m^-2 yr^-1 into surface waters of the central Labrador Sea. A mixed layer carbon budget yields a net community production of 4.0 ± 0.8 mol C m^-2 during the 2005 productive season about one third of which appears to undergo subsurface respiration in a depth range that is reventilated during the following winter. The timing of the spring bloom is discussed and eddies from the West Greenland Current are thought to be associated with the triggering of the bloom. Finally, we use CO₂ and O₂ mixed layer dynamics during the 2005 spring bloom to evaluate a suite of prominent wind speed-dependent parameterizations for the gas transfer coefficient. We find very good agreement with those parameterizations which yield higher transfer coefficients at wind speeds above 10 m s^-1.