Inorganic carbon in the Labrador Sea: Estimation of the anthropogenic component

Abstract

The intermediate and deep waters of the Labrador Sea are dominated by recently ventilated water masses (ventilation ages <20 yr). Atmospheric gases such as CO 2 and chlorofluorocarbons are incorporated into these water masses at the time of formation and subsequently transported via boundary currents into the North Atlantic interior. Recent measurements of total carbonate were used in tandem with total alkalinity and oxygen to estimate the levels of anthropogenic carbon dioxide in the Labrador Sea region. Upper water column anthropogenic CO 2 estimated in this manner showed good agreement with levels calculated from CO 2 increase in the atmosphere. In spring 1997, anthropogenic contributions to total carbonate (CTant) were 40±3 μmol/kg in water penetrated by deep convection the previous winter and slightly lower (37±2 μmol/kg) in the deeper convective layer formed in the winters of 1992–1994. Consistent with the concurrent profiles of CFC-11, levels decrease into the older NEADW (North East Atlantic Deep Water) with levels of 30±3 μmol/kg and then increase near bottom within the layer of DSOW (Denmark Strait Overflow Water). The distribution of CTant shows the flow of new LSW southwards with the western boundary current and also eastwards into the Irminger Sea. We estimate that 0.15–0.35 Gt carbon of anthropogenic origin flow through the Labrador Sea within the Western Boundary Undercurrent per year.