Decadal changes of anthropogenic carbon in the Atlantic 1990–2010
Abstract. The Atlantic inventory of anthropogenic carbon (Cant) and its changes between 1990 and 2010 are investigated by applying the transit time distribution (TTD) method to anthropogenic tracer data. In contrast to previous TTD applications, here we take into account the admixture of old waters free of anthropogenic tracers. The greatest difference to other methods based on direct carbon observations is the higher Cant storage in the deep ocean. The results from the TTD method better reflects the observed distribution of other transient tracers such as chlorofluorocarbons (CFCs). Changes in oceanic circulation/ventilation are important on the regional scale. The enhanced upwelling of older water in the Southern Ocean and the decline in the convection depth in the Labrador Sea lead to deviations of the inferred Cant increase between 1990 and 2010 from the rate equivalent to a steady state ocean. For the total Atlantic Cant inventory, however, decadal ventilation variability of individual water masses is partially compensating each other, and the effect is small due to the much higher flushing time for the total Atlantic of the order of hundreds of years. The total Cant inventory increases from 39.7 ± 7.7 Pg C in 1990 to 54.6 ± 9.5 Pg C in 2010, almost in unison with the rising CO2 in the atmosphere. Only a reduction of the Atlantic ventilation over several decades would severely change this relationship.
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