A decade-long biogeochemical cruise time-series from the Salish Sea and Washington coast: Regional connections to large-scale ocean climate drivers of ocean acidification and hypoxia

Coastal and estuarine waters of the northern California Current Ecosystem and southern Salish Sea benefit from a comprehensive observation network for detecting and illuminating ocean acidification and hypoxia dynamics. Given the vulnerability of North Pacific ecosystems to ocean acidification and hypoxia, these observations provide critical insight into interactions among natural and anthropogenic processes as well as their combined effects on these valuable ecosystems. This time-series provides synoptic snapshots of conditions in Washington’s coastal and estuarine waters during conditions encompassing all ENSO phases and seasons, as well as throughout the North Pacific marine heat wave of 2013–2016. The cruises obtained high-quality carbon, physical, and other biogeochemical parameters through a combination of CTD casts to measure temperature, conductivity, pressure, and oxygen profiles and discrete water samples for analysis of dissolved inorganic carbon, oxygen, total alkalinity, and nutrient concentrations, with all carbonate system parameters calculated from these measured quantities. We compared average properties for each cruise with contemporaneous values of the North Pacific Gyre Oscillation (NPGO) index, Pacific Decadal Oscillation (PDO) index, Oceanic Niño Index (ONI), and Bakun upwelling anomaly for 48°N, as well as daylength (proxy for seasonality) and global atmospheric pCO2 (proxy for directional climate change). Preliminary regression results point to important roles for PDO, NPGO, seasonality, and directional climate change in shaping the biogeochemical dynamics of the southern Salish Sea. We anticipate these relationships will vary with water depth and sub-region within the study area upon further analysis and will provide a useful comparison to model results attributing variability to various drivers. This joint UW–PMEL observing effort has been supported by several state and federal funding sources. All observations meet or exceed the monitoring guidelines of the Global Ocean Acidification Observing Network, the U.S. National Oceanic and Atmospheric Administration\u27s Ocean Acidification Program, and ocean carbon community best practices