How Is the Ocean Anthropogenic Carbon Reservoir Filled?
Xabier Dávila, Geoffrey Gebbie, Ailin Brakstad, Siv K. Lauvset, Elaine L. McDonagh, Jörg Schwinger, Are Olsen
Abstract
Abstract About a quarter of the total anthropogenic CO 2 emissions during the industrial era has been absorbed by the ocean. The rate limiting step for this uptake is the transport of the anthropogenic carbon (C ant ) from the ocean mixed layer where it is absorbed to the interior ocean where it is stored. While it is generally known that deep water formation sites are important for vertical carbon transport, the exact magnitude of the fluxes across the base of the mixed layer in different regions is uncertain. Here, we determine where, when, and how much C ant has been injected across the mixed‐layer base and into the interior ocean since the start of the industrialized era. We do this by combining a transport matrix derived from observations with a time‐evolving boundary condition obtained from already published estimates of ocean C ant . Our results show that most of the C ant stored below the mixed layer are injected in the subtropics (40.1%) and the Southern Ocean (36.0%), while the Subpolar North Atlantic has the largest fluxes. The Subpolar North Atlantic is also the most important region for injecting C ant into the deep ocean with 81.6% of the C ant reaching depths greater than 1,000 m. The subtropics, on the other hand, have been the most efficient in transporting C ant across the mixed‐layer base per volume of water ventilated. This study shows how the oceanic C ant uptake relies on vertical transports in a few oceanic regions and sheds light on the pathways that fill the ocean C ant reservoir.