# A century of change in the California Current: upwelling system amplifies acidification

## TL;DR

The California Current and Salish Sea have experienced faster acidification than expected due to a combination of human-caused CO2 and natural processes.

## Contribution

The study uses boron isotopes in corals to show that acidification in the CCS has been amplified beyond atmospheric CO2 levels.

## Key findings

- Boron isotope analysis reveals acidification in the CCS and Salish Sea has exceeded atmospheric CO2 trends.
- Future projections suggest continued rapid acidification, threatening marine ecosystems.
- Thermodynamic buffering effects interact with anthropogenic CO2 to amplify acidification.

## Abstract

Predicting the pace of acidification in the California Current System (CCS), a productive upwelling system that borders the west coast of North America, is complex because the anthropogenic contribution is intertwined with other natural sources. A central question is whether acidification in the CCS will follow the pace of increasing atmospheric CO2, or if climate effects and other biogeochemical processes will either amplify or attenuate acidification. Here, we apply the boron isotope pH proxy to cold-water orange cup corals to establish a historic level of acidification in the CCS and the Salish Sea, an associated marginal sea. Through a combination of complementary modeling and geochemical approaches, we show that the CCS and Salish Sea have experienced amplified acidification over the industrial era, driven by the interaction between anthropogenic CO2 and a thermodynamic buffering effect. From this foundation, we project future acidification in the CCS under elevated CO2 emissions. The projected change in pCO2 over the 21st century will continue to outpace atmospheric CO2, posing challenges to marine ecosystems of biological, cultural, and economic importance.

Boron isotopes in cold-water corals reveal that acidification in the California Current and Salish Sea has outpaced atmospheric CO2 over the industrial era, posing a threat to ecosystems of ecological, cultural and economic value.