Pacific-Arctic Ocean Acidification: Decadal Trends and Drivers

Abstract

This study presents the first regional-scale analysis to quantify decadal trends and drivers of surface ocean acidification (OA) across the highly sensitive Pacific-Arctic Region (PAR) using a consistent trend methodology. From 1993 to 2021, the Southern PAR acidified at rates comparable to the global average, with ${\text{pH}}_T$ declining by 0.018 units ${\text{dec}}^{-1}$ and aragonite saturation state $\left({\Omega }_{\text{Ar}}\right)$ decreasing by 0.063 units ${\text{dec}}^{-1}$, primarily driven by anthropogenic ${\text{CO}}_2$ uptake. In contrast, the Bering Strait exhibited slower acidification, with ${\text{pH}}_T$ declining by 0.011 units ${\text{dec}}^{-1}$ and ${\Omega }_{\text{Ar}}$ decreasing by 0.020 units ${\text{dec}}^{-1}$—substantially lower than previously reported—likely due to increased primary productivity. The Northern PAR experienced the most rapid acidification: ${\text{pH}}_T$ decreased by 0.028 units ${\text{dec}}^{-1}$ and ${\Omega }_{\text{Ar}}$ by 0.078 units ${\text{dec}}^{-1}$, with the Beaufort Gyre acidifying 2–4 times faster than the global mean. This rapid change was driven by rising atmospheric ${\text{CO}}_2$ and significant freshening linked to sea ice melt and increased riverine input, which reduced the ocean's buffering capacity. Continued warming will likely exacerbate acidification in regions transitioning from multi-year to seasonal ice. While local processes such as primary productivity can temporarily counteract OA, whether they can offset rising anthropogenic ${\text{CO}}_2$ levels remains unclear. This underscores the importance of biogeochemical models that integrate climatic and biological feedbacks, enabling accurate forecasts of OA changes and their impacts on marine ecosystems. These findings highlight the urgent need for sustained monitoring in the PAR, where accelerating changes threaten critical ecosystems.