FY 2023 Decadal trends in the oceanic storage of anthropogenic carbon from 1994 to 2014 Müller, J.D., N. Gruber, N. Lange, D. Zhu, S.K. Lauvset, A. Olsen, T. Tanhua, M. Ishii, B.R. Carter, F.F. Pérez, C.L. Sabine, R. Wanninkhof, A. Murata, and R.A. Feely AGU Advances, 4(4), e2023AV000875, doi: 10.1029/2023AV000875, View open access article at AGU/Wiley (external link) (2022) The oceanic uptake and resulting storage of the anthropogenic CO2 (Cant) that humans have emitted into the atmosphere moderates climate change. Yet our knowledge about how this uptake and storage has progressed in time remained limited. Here, we determine decadal trends in the storage of Cant by applying the eMLR(C*) regression method to ocean interior observations collected repeatedly since the 1990s. We find that the global ocean storage of Cant grew from 1994 to 2004 by 29 ± 3 Pg C dec−1 and from 2004 to 2014 by 27 ± 3 Pg C dec−1 (±1σ). The storage change in the second decade is about 15 ± 11% lower than one would expect from the first decade and assuming proportional increase with atmospheric CO2. We attribute this reduction in sensitivity to a decrease of the ocean buffer capacity and changes in ocean circulation. In the Atlantic Ocean, the maximum storage rate shifted from the Northern to the Southern Hemisphere, plausibly caused by a weaker formation rate of North Atlantic Deep Waters and an intensified ventilation of mode and intermediate waters in the Southern Hemisphere. Our estimates of the Cant accumulation differ from cumulative net air-sea flux estimates by several Pg C dec−1, suggesting a substantial and variable, but uncertain net loss of natural carbon from the ocean. Our findings indicate a considerable vulnerability of the ocean carbon sink to climate variability and change. Plain Language Summary. The ocean takes up about 30% of the anthropogenic CO2 that is emitted to the atmosphere by human activities. The removal of this anthropogenic CO2 from the atmosphere counteracts climate change. The rate at which the ocean takes up anthropogenic CO2 is controlled by its transport from the surface to the depth of the ocean, where most of it accumulates. Thus, we can quantify and understand the oceanic uptake by keeping track of the accumulation of anthropogenic CO2 in the ocean interior. In this study, we use a global collection of measurements of CO2 in seawater to infer the temporal evolution of this accumulation between 1994 and 2014. We find that the ocean continued to act as a strong sink for CO2 over this period, removing, on average, nearly 30 billion tons of carbon per decade. However, we also detect a possible weakening of this uptake, since the accumulation of anthropogenic CO2 during the second decade was not as large as expected from the increase in atmospheric CO2. Our findings suggest that the ocean sink for CO2 might further shrink as climate change progresses. Feature Publications | Outstanding Scientific Publications Contact Sandra Bigley | Help
