Dissimilar Sensitivities of Ocean Acidification Metrics to Anthropogenic Carbon Accumulation in the Central North Pacific Ocean and California Current Large Marine Ecosystem

We analyze and compare changes in ocean acidification metrics caused by anthropogenic carbon (Canth) accumulation in the North Pacific Ocean and California Current Large Marine Ecosystem (CCLME). The greatest declines in pH and carbonate mineral saturation state occur near the surface, coincident with the highest Canth concentrations. However, maximal increases in the partial pressure of carbon dioxide (pCO2) and hydrogen ion concentration occur subsurface where Canth values are lower. We attribute dissimilar sensitivities of these metrics to background ocean chemistry, which has naturally high pCO2 and low buffering capacity in subsurface waters due to accumulated byproducts of organic matter respiration, which interacts with Canth. In the CCLME, rising subsurface pCO2 has increased the frequency, duration, and intensity of hypercapnia (pCO2 ≥ 1,000 μatm) on the continental shelf. Our findings suggest that hypercapnia induced by Canth accumulation can co‐occur with hypoxia in the CCLME and is an additional modern stressor for marine organisms.