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 (C_ant) and its consequences remain unclear. Here, we show prominent transport of C_ant (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 C_ant 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 C_ant 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 (C_ant), 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 C_ant and a visible pattern of relatively high concentration of C_ant along the AABW formation pathway, and the concentration of C_ant 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.