Summary
This observational study demonstrates that the Southern Annular Mode—a major climate variability pattern—modulates ocean acidification rates in the Southern Ocean independently of, and superimposed upon, rising atmospheric CO₂. Enhanced westerly winds during positive SAM phases drive increased meridional Ekman transport and vertical mixing, delivering more acidified subsurface and high-latitude waters to surface layers in the Antarctic Zone, resulting in pH and carbonate saturation declines faster than CO₂ forcing alone would predict.
UK applicability
The findings have limited direct applicability to UK farming or land-based food systems. However, they contribute to understanding of climate-driven changes in Southern Ocean productivity and marine ecosystem resilience, which may indirectly affect global fish stocks and UK-sourced seafood supply chains.
Key measures
Surface water pH, aragonite saturation state, atmospheric CO₂ concentrations, Southern Annular Mode index, westerly wind strength, meridional Ekman transport, vertical mixing rates
Outcomes reported
The study measured surface water pH and aragonite saturation state in the Southern Ocean south of Tasmania across two latitudinal zones (Antarctic Zone 60°–55° S and Subantarctic Zone 50°–45° S) during periods of positive Southern Annular Mode trends. It reported differential acidification rates between zones, with accelerated surface acidification at higher southern latitudes exceeding predictions from atmospheric CO₂ increase alone.
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