Low-oxygen conditions occur deep in the continental shelves of Oregon and Washington, during sustained periods of coastal upwelling. When combined with low river discharges, those conditions may also lead to oxygen depletion in Pacific Northwest estuaries, and in particular in the Columbia River estuary (Roegner 2010).
Ecological implications of low oxygen conditions are significant. Shelf hypoxia may lead to displacement or death by suffocation of marine organisms, as exemplified by massive fish kills off the Washington coast in 2006. In the Columbia River estuary, growing concerns exist regarding the role of low oxygen on salmon survival.
CMOP has maintained an oxygen watch for both the WA shelf (since April 2009) and the Columbia River estuary (since June 2010). Both watches are direct uses of data from the SATURN observation network. SATURN is a signature technology of CMOP, developed with the support of the National Science Foundation (OCE-0424602), the Northwest Association for Networked Ocean Observing Sustems, and regional stakeholders.
For the WA shelf, the watch is based on the deployment of a Slocum glider, in collaboration with the Quinault Indian Nation. Thresholds of reference for dissolved oxygen (DO) are adopted from the PISCO program: mild hypoxia starts at 1.4ml/l, and severe hypoxia at 0.5ml/l.
For the Columbia River estuary, the watch is based on endurance stations in the south (SATURN-03, since June 2010) and north channels (SATURN-01, starting August 2010), and is collaboration with NOAA Northwest Fisheries Science Center and the Lower Columbia River Estuary Partnership. The focus is on conditions that might affect salmon out migration to the ocean. The thresholds of reference are 2.1ml/l (acute mortality; source: EPA 1986) and 4.3 ml/l (incipient response; source: Davis 1975).
Each watch includes (a) automated near real-time (when instrumentation is deployed) and archival graphical representations of prevailing conditions and (b) event-driven annotations on an “oxygen blog”. Dissolved oxygen sensors are expected to be deployed year-round in SATURN-01 and SATURN-03 (except for operational downtimes). Glider missions are flown April-October; while significant variations occur for operational reasons, the target duration is 3-4 weeks per mission, with 1-2 weeks of downtime between missions.
Davis J.C. (1975) Minimal dissolved oxygen requirements of aquatic life with emphasis on Canadian species: a review. J Fish Res Bd Canada 32: 2295–2332
Environmental Protection Agency (1986) Ambient water quality criteria for dissolved oxygen. EPA 440/5-86-003
Roegner, G.C. (2010), Coastal upwelling supplies low dissolved oxygen water to the Columbia River estuary. Eos Trans. AGU, 91(26), Ocean Sci. Meet. Suppl., Abstract BO35D-04