Paired windward and leeward biogeochemical time series reveal consistent surface ocean CO sub(2) trends across the Hawaiian Ridge

Sustained time series have provided compelling evidence for progressive acidification of the surface oceans through exchange with the growing atmospheric reservoir of carbon dioxide. However, few long-term programs exist, and extrapolation of results from one site to larger oceanic expanses is hampered by the lack of spatial coverage inherent to Eulerian sampling. Since 1988, the Hawaii Ocean Time-series program has sampled CO sub(2) system variables nearly monthly at Station ALOHA, a deep ocean site windward and 115km north of the island of Oahu. Surface measurements have also been made at Station Kahe, a leeward site 12km from the island and on the opposite side of the Hawaiian Ridge. Despite having different physical settings, the sites exhibit identical rates of surface pCO sub(2) increase and hydrogen ion accumulation, suggesting that atmospheric forcing dominates over local dynamics in determining the CO sub(2) trend in the surface waters of the North Pacific subtropical gyre. Key Points * Annual cycles and secular trends explain much surface CO sub(2) temporal variability * Physically contrasting time-series sites yield common biogeochemical trends * Ocean acidification rates on either side of the Hawaiian Ridge are identical