The Indian Ocean (IO) surface acidification is governed by pronounced regional variability that is inadequately resolved in coarse-resolution CMIP6 models. Here, we employ eddy-resolving, dynamically downscaled outputs from three CMIP6 Earth System Models under the high-emissions SSP5-8.5 scenario to project future changes in IO acidification, with the model ensemble selected to account for uncertainty in future projections. Eddy-resolving simulations improve representation of mesoscale-driven surface acidification variability by ∼5%–10% relative to CMIP6 models, particularly in coastal regions, while reducing inter-model spatio-temporal heterogeneity. The analysis indicates a relatively weaker mean increase in [H+] compared with CMIP6 projections. The downscaled models yield a dynamically consistent, improved representation of the seasonal cycle of [H+] compared to CMIP6 models, particularly in the northern IO. This facilitates a more robust assessment of future anthropogenically driven changes in [H+] amplitude, with the monthly composite amplitude projected to increase by ∼63%–83% during the far-future period (FF; 2071–2100) across the IO. However, in the Arabian Sea, the increase is ∼37% smaller than in CMIP6, whereas other regions exhibit largely comparable changes. This amplification is primarily driven by enhanced sensitivity of [H+] to surface temperature and dissolved inorganic carbon under warming and increased CO2 uptake. Consistent with these changes, acidification extremes intensify (∼26%–45%) and become more frequent (∼3–5 times higher) in FF. Notably, in coastal regions after 2070, anthropogenic acidification signals emerge later in the downscaled projections than in CMIP6. These results highlight the need for high-resolution projections to improve estimates of future IO acidification and its associated risks.
Ghoshal P. K., Joshi A. P., & Chakraborty K., 2026. Does the evolution of Indian Ocean acidification follow CMIP6 projections under a high-emission scenario? Journal of Geophysical Research: Oceans 131: e2026JC024515. doi: 10.1029/2026JC024515. Article (subscription required).
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