Anthropogenic carbon storage and its decadal changes in the Atlantic between 1990–2020

• Published in: Biogeosciences
• Main Authors: Steinfeldt, Reiner, Rhein, Monika, Kieke, Dagmar
• Format: Text
• Language: English
• Published: 2024
• Subjects: Southern Ocean; Labrador Sea; North Atlantic
• Online Access: https://doi.org/10.5194/bg-21-3839-2024; https://bg.copernicus.org/articles/21/3839/2024/

The Atlantic inventory of anthropogenic carbon ( C ant ) and its changes between 1990 and 2020 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 from other methods based on direct carbon observations is the higher C ant storage in the deep ocean. Estimations of the decadal C ant increase based on direct carbon observations yield in general a smaller share of C ant storage in the North Atlantic and a larger share in the South Atlantic compared to our results. Changes in oceanic circulation and/or ventilation have significant impacts on the C ant inventory on the regional scale. The enhanced upwelling of older water in the Southern Ocean and the variability in the convection depth in the Labrador Sea lead to deviations in the inferred C ant increase between 1990 and 2020 from the rate equivalent to a steady-state ocean. For the total Atlantic C ant inventory, however, decadal ventilation variability of individual water masses partially compensates for each other. In addition, its impact on the C ant storage is small due to the much higher flushing time for the whole Atlantic of the order of hundreds of years. The total C ant inventory increases from 43.0 ± 7.3 Pg C in 1990 to 68.2 ± 10.8 Pg C in 2020, almost in unison with the rising CO 2 in the atmosphere. So far, ventilation changes have impacted the C ant concentrations only on the regional scale, especially in the subpolar North Atlantic and the Southern Ocean.