Oceanographic Processes on North-Central California Margin Plankton: A Heatwave and a Decade of Carbonate Chemistry.

Increasing anthropogenic carbon dioxide emissions are rapidly changing coastal ocean systems through increasing temperature, ocean acidification, and hypoxia, and potentially intensified upwelling. As the base of the food web, plankton are useful indicators of the impacts of these parameters on marine organisms. We investigated the strength, timing, duration, and co-occurrence of temperature, wind stress, carbonate chemistry, and oxygenation on size and abundance of crustacean plankton indicator species off the north-central Californian coast (38˚N, 123.5˚W). This region is well studied in terms of surface water productivity, oceanographic variability, and more recently, carbon chemistry and climate impacts through the Applied California Current Ecosystem Studies (ACCESS) partnership. ACCESS cruises survey the waters within and around the Greater Farallones and Cordell Bank National Marine Sanctuaries three times annually, sampling water column hydrography and discrete water samples from 1 m and 200 m depth at five stations along three primary transects. Here we present regional carbonate chemistry for the most recent decade that spans before, during, and after the 2014-2016 northeast Pacific marine heatwave, along with size distribution and biomass abundance of crustacean plankton like krill from 2005 to 2018. We found that the 2014-2016 heatwave ameliorated ocean acidification e.g. during the heatwave, aragonite saturation states at the surface of Line 6 Station W rose to Ω>2 compared to around Ω=1.1 during typical upwelling conditions. Additionally, we found smaller Euphausia pacifica during the heatwave. This work aims to understand regional interannual oceanographic variability in temperature, carbonate chemistry, and oxygenation and their impact on zooplankton, which are of import to both surface and deep-sea food webs due to export.