The longest ocean time series of dissolved carbon dioxide in the Pacific — part of the “Keeling Curve of the ocean” — is revealed.
For the first time, scientists at UC San Diego’s Scripps Institution of Oceanography have published nearly four decades’ worth of dissolved carbon dioxide measurements from waters off Southern California. The measurements reveal a slight but consistent trend of ocean acidification, a process characterized by a decrease in the ocean’s pH over time due to its absorption of carbon dioxide (CO2) from the atmosphere.
Since the early 1980s, samples of ocean carbonate chemistry have been collected by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) program, which was established in 1949 to investigate the collapse of the sardine population off California. In a new study, Scripps Oceanography researchers present 37 years of measurements from CalCOFI Line 90 Station 90 (station 90.90), a measuring site located 450 kilometers (280 miles) off the coast of San Diego. The team’s findings were published on Nov. 3 in Communications Earth & Environment, a journal affiliated with Nature.

The measurements from station 90.90 establish the oldest time series of direct inorganic carbon observations in the Pacific Ocean. While measurements at the station carry on to the present day, the study details quarterly measurements collected from 1984 to 2021, with a gap from 2002 to 2008 due to a lack of funding. Notably, the data show that the seawater at the study site is getting more acidic, with a measured decrease in pH of 0.0015 per year.
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