Temporal variability of the anthropogenic CO₂ storage in the Irminger Sea

Abstract. The anthropogenic CO₂ (C_ant) estimates from cruises spanning more than two decades (1981–2006) in the Irminger Sea area of the North Atlantic Subpolar Gyre reveal a large variability in the C_ant storage rates. During the early 1990's, the C_ant storage rates (2.3±0.6 mol C m⁻² yr⁻¹) doubled the average rate for 1981–2006 (1.1±0.1 mol C m⁻² yr⁻¹), whilst a remarkable drop to almost half that average followed from 1997 onwards. The C_ant storage evolution runs parallel to chlorofluorocarbon-12 inventories and is in good agreement with C_ant uptake rates of increase calculated from sea surface pCO₂ measurements. The contribution of the Labrador Seawater to the total inventory of C_ant in the Irminger basin dropped from 66% in the early 1990s to 49% in the early 2000s. The North Atlantic Oscillation shift from a positive to a negative phase in 1996 led to a reduction of air-sea heat loss in the Labrador Sea. The consequent convection weakening accompanied by an increase in stratification has lowered the efficiency of the northern North Atlantic CO₂ sink.