Dissimilar Sensitivities of Ocean Acidification Metrics to Anthropogenic Carbon Accumulation in the Central North Pacific Ocean and California Current Large Marine Ecosystem. Issue 15 (12th August 2022)

• Record Type: Journal Article
• Authors: Arroyo, Mar C.; Fassbender, Andrea J.; Carter, Brendan R.; Edwards, Christopher A.; Fiechter, Jerome; Norgaard, Addie; Feely, Richard A.
• Is Part Of: Geophysical research letters. Volume 49:Issue 15(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-12
• Subjects: ocean acidification -- revelle factor -- hypercapnia -- carbon cycle -- California Current Large Marine Ecosystem -- North Pacific Ocean; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL097835
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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 ( p CO2 ) 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 p CO2 and low buffering capacity in subsurface waters due to accumulated byproducts of organic matter respiration, which interacts with Canth . In the CCLME, rising subsurface p CO2 has increased the frequency, duration, and intensity of hypercapnia ( p CO2 ≥ 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. Plain Language Summary: The ocean mitigates the extent of global warming by absorbing a portion of the carbon dioxide gas (CO2 ) released into the atmosphere by human activities. However, this comes at a cost to ocean health because the uptake of this anthropogenic CO2 causes changes in ocean chemistry, called ocean acidification (OA), that can be detrimental to marine ecosystems. This study explores how OA metrics have changed in the upper waters of the open North Pacific Ocean and coastal California Current Large Marine Ecosystem (CCLME). We focus on the CCLME due to its global importance and economically important fisheries. We find that different OA metrics exhibit different patterns of change with depth in the water column due to the natural, background ocean chemistry. One such metric shows that there is now more subsurface water containing CO2 levels elevated enough to threaten the health of marine organisms than there was before the anthropogenic CO2 addition. Our finding of expanded volumes of water with high‐CO2 levels near the coast is important to consider as a source of stress for marine organisms living both on the seafloor and in the water column. Key Points: Naturally high subsurface p CO2 and Revelle Factors cause greater sensitivities of p CO2 and [H + ] to anthropogenic carbon at depth Hypercapnic conditions have expanded by 58%–94% in waters above 750 m along the US West Coast since industrialization Modern hypercapnic events at the continental shelf break are more frequent and intense in the northern California Current