UC San Diego

Seawater CO2-chemistry in the Southern California Bight (SCB) has been well characterized at seasonal resolution over the past several decades by multiple research expeditions. However, the near-shore environment (0-2 km) has largely been absent from these surveys and the drivers of seawater CO2-chemistry variability in this region remain to be fully characterized. In particular, the role of variable upwelling intensity is poorly known, and could have important implications for near-shore habitats sensitive to low pH and ΩAr conditions. Here, I present near-shore seawater CO2-chemistry data based on monthly transects between March 2017 and September 2018 at four stations extending from the Scripps Pier to the 60 m depth contour (~2 km offshore). Seawater samples were analyzed for seawater CO2-chemistry parameters and were paired with autonomous sensors deployed at 18 m depth. The results showed that during fall and winter, pH and ΩAr values ranged from 7.9-8.1 and 1.8-2.9 along the transect, respectively. During spring and summer, intensified upwelling transported low pH and ΩAr seawater to the near-shore region reaching values as low as 7.69 and 0.95, respectively, at depths less than 20 m and within 1 km of the shoreline. The low pH and ΩAr conditions typically persisted for several months from April to July. The magnitude of change in pH and ΩAr was correlated with the density of the water, i.e., the higher the density the lower the pH and ΩAr, but did not show direct correlation with the total amount of water that was upwelled.