Winter influences on Summer Hypoxia Variability

Samantha Siedlecki, University of Connecticut, Department of Marine Sciences, Groton, United States, Parker MacCready, University of Washington, School of Oceanography, Seattle, United States, Ryan M McCabe, University of Washington, Joint Institute for the Study of the Atmosphere and Ocean, Seattle, WA, United States, Neil Banas, University of Strathclyde, Glasgow, United Kingdom, Kristen A Davis, University of California Irvine, Civil and Environmental Engineering, Irvine, United States, Sarah N Giddings, University of Washington, Seattle, WA, United States, Burke R Hales, Oregon State Univ, Corvallis, OR, United States, Jack A Barth, Oregon State University, Marine Studies Initiative, Corvallis, OR, United States and Scott Michael Durski, Oregon State University, Earth, Ocean, and Atmospheric Sciences, Corvallis, United States
Abstract:
Low dissolved oxygen and hypoxic events are increasingly common in the Northern California Current System (N-CCS), and projected to become more intense and persist over more of the upwelling season in the future. As a highly productive seasonal upwelling system, the region supports economically important fisheries vulnerable to these events. While predictive skill for bottom oxygen concentrations exists in forecasts for the region on seasonal timescales, a mechanism explaining this predictability and to describe the driving forces behind interannual variability in severity of hypoxic conditions remains elusive. Here we show that the average wind stress of the preceding winter downwelling season is significantly correlated with the hypoxic volume of the following upwelling season using an analysis of a regional oxygen simulation. Years exhibiting stronger winter downwelling experience higher depth-averaged nutrients within the mixed layer and then higher volumes of hypoxic waters during the following upwelling season. The deeper the mixed layer depth, the more nutrients are entrained from below and/or the more integrated respiration from falling particles occurs within that layer. We identify a local amplifying mechanism for an atmospheric ENSO teleconnection with important implications for seasonal forecasts of biogeochemistry and future projections in the region.
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