National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2024

Transport of anthropogenic carbon from the Antarctic shelf to deep Southern Ocean triggers acidification

Zhang, S., Y. Wu, W.-J. Cai, Z. Wang, R.A. Feely, W. Cai, Y. Wang, C. Liu, X. Li, Q. Yang, M. Ding, Z. Xu, Y. Luo, X. Cheng, L. Chen, and D. Qi

Global Biogeochem. Cycles, 37(12), e2023GB007921, doi: 10.1029/2023GB007921, View article online at Wiley/AGU (external link) (2023)

Flow of dense shelf water provide an efficient mechanism for pumping CO2 to the deep ocean along the continental shelf slope, particularly around the Antarctic bottom water (AABW) formation areas where much of the global bottom water is formed. However, the contribution of the formation of AABW to sequestering anthropogenic carbon (Cant) and its consequences remain unclear. Here, we show prominent transport of Cant (25.0 ± 4.7 Tg C yr−1) into the deep ocean (>2,000 m) in four AABW formation regions around Antarctica based on an integrated observational data set (1974–2018). This maintains a lower Cant in the upper waters than that of other open oceans to sustain a stronger CO2 uptake capacity (16.9 ± 3.8 Tg C yr−1). Nevertheless, the accumulation of Cant can further trigger acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr−1. Our findings elucidate the prominent role of AABW in controlling the Southern Ocean carbon uptake and storage to mitigate climate change, whereas its side effects (e.g., acidification) could also spread to other ocean basins via the global ocean conveyor belt.

Plain Language Summary. The Southern Ocean is thought to uptake and store a large amount of anthropogenic CO2 (Cant), but little attention has been paid to the Antarctic coastal regions in the south of 60°S, mainly due to the lack of observations. Based on an integrated data set, we discovered the deep penetration of Cant and a visible pattern of relatively high concentration of Cant along the AABW formation pathway, and the concentration of Cant along the shelf-slope is higher than that of other marginal seas at low-mid latitudes, implying a highly effective Cant transport in AABW formation areas. We also found strong upper-layer CO2 uptake and a significant acidification rate in the deep waters of the Southern Ocean due to the AABW-driven CO2 transport, which is 3 times faster than those in other deep oceans. It is therefore crucial to understand how the Antarctic shelf regions affect the global carbon cycle through the uptake and transport of anthropogenic CO2, which also drives acidification in the other ocean basins.

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