results - hypoxia (low dissolved oxygen)

Recent paper by Siedlecki et al., 2015 in JGR on the seasonal and interannual oxygen variability on the Washington and Oregon continental shelves

The paper highlights hotspots for hypoxia as retentive regions where resipiration is high. The paper also explains that both respiration and circulation-driven divergence are important to the Washington coast oxygen budget while resipiration dominates the Oregon coast.

Figure 1. Movie of 2005 hypoxia

The left two panels show surface salinity (a) and surface temperature (b) respectively. The third panel (c) shows the surface chlorophyll concentration, i.e. the amount of phytoplankton. The right panel (d) shows the bottom oxygen where the white line is the 100m isobath and the dark blue indicates hypoxic water (water less than 1.5mL/L of dissolved oxygen). The bottom panel (e) indicates the along-shore wind stress (black) and an 8d weighted mean wind (gray, Austin & Barth 2002).

spatial variability

The biogeochemical model is used to examine spatial variability of low dissolved oxygen, or hypoxia. Hypoxia is dangerous for many marine species leading to occasional large die-offs of organisms such as the events in summer of 2002 and 2006 (see Connolly et al. 2010 , Chan et al. 2008, and T. Connolly's website for more information). Comparisons between low oxygen zones in the model and observations are strong giving us confidence in using the model in order to investigate the causes for this spatial variability.

temporal variability

The modeled temporal variability in oxygen matches the observed variability including the seasonal decline in bottom oxygen concentrations during the summer upwelling periods (winds from the north). Winds from the north lead to offshore Ekman transport and thus upwelling of salty, cold, low oxygen, nutrient-rich water. The nutrients fuel a bloom of phytoplankton (chlorophyll in the movie above) at the surface and the resulting biomass decays mostly on the shelf further depleting oxygen concentrations. The local decay of biomass produces hypoxic conditions on the shelf in the model, confirming the results of Connolly et al. 2010. Althought the model has only been run for four years, we see interesting patterns that suggest important inter-annual variability of hypoxia. Please see SA Siedlecki's website for more information.

seasonal forecasts

The model is now also being run in a predictive mode. Seasonal forecasts (6-9 months) are being produced by the JISAO Seasonal Coastal Ocean Prediction of the Ecosystem (J-SCOPE) program in order to provide forecasts of ocean conditions relevant to management decisions and ecosystem health. Please see the J-SCOPE website and SA Siedlecki's website for more information.