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

Abstract

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.

Key points

• We show evidence for the accumulation of C_ant along the Antarctic shelf-slope into the deep ocean
• The process of AABW formation drives C_ant downward transport at 25.0 ± 4.7 Tg C yr⁻¹, sustaining the CO₂ uptake in the surface ocean
• This further triggers acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr⁻¹, which is faster than in other deep oceans

Zhang S., Wu Y., Cai W.-J., Cai W., Feely R. A., Wang Z., Tanhua T., Wang Y., Liu C., Li X., Yang Q., Ding M., Xu Z., Kerr R., Luo Y., Cheng X., Chen L. & Qi D., 2023. Transport of anthropogenic carbon from the Antarctic shelf to deep Southern Ocean triggers acidification. Global Biogeochemical Cycles 37: e2023GB007921. doi: 10.1029/2023GB007921. Article (subscription required).

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