N0. 32. Oceanic

David H. Johnson

Geographic Setting. Deep water (>656 ft [200 m] deep), open areas of the northeast Pacific Ocean extending seaward from the 656-ft (200-m) isobath along the outer coast of Washington and Oregon.

Physical Setting. This habitat includes the continental slope, which is generally found at depths between the 656- and 6,560-ft (200- and 2,000-m) isobath. In general, the 656-ft (200-m) isobath follows a north-south line.

Landscape Setting. The Oceanic habitat adjoins the shallower marine waters of the Marine Shelf habitat.

Structure. The oceanic area off Oregon and Washington includes marine waters >656 ft (200 m) deep. This region can be divided into 2 general habitats reflecting geomorphic features and water depth.

The continental shelf along Oregon is characterized by a series of oceanic banks including Daisy, Stonewall, Perpetua, Heceta, and Silcoos banks, and a major promontory, Cape Blanco. In contrast, the Washington shelf is furrowed by Nitinat, Juan de Fuca, Quinault, Grays, Guide, Willapa, and Astoria submarine canyons, remnants of the last glacial period.

The continental slope is usually defined as depths between 656 and 6,560 ft (200 and 2,000 m) deep. Beyond the slope is a more gradual sloping area known as the continental rise. The rise eventually terminates at the abyssal sea floor (approximately 13,120 ft [4,000 m] deep). Boundaries between the rise and abyssal plain are not clearly distinct. Both the rise and abyssal sea floor are composed largely of mud.

Marine currents define important aspects of this habitat, as wind-driven equatorward surface flow in the spring and summer results in episodic upwelling of cold nutrient-rich water; the poleward surface flow in the autumn and winter is when the downwelling prevails. The transition from poleward to equatorward flow occurs abruptly in the spring and the reverse transition occurs somewhat less abruptly in the autumn.

Other Classifications and Key References. A number of oceanographic studies have attempted to identify distinct features or parameters to define the geographical extent of the Subarctic and Subtropical Pacific waters. These studies were based mostly on temperature-salinity properties and oxygen-salinity curves ^{73, 213}. Favorite et al. ⁸³ and Thomson ²⁰³ discussed new information and terminology for the oceanic systems in the Northeast Pacific. A recent review by Bottom et al. ³³ synthesized existing information on the characteristics of the ocean environment and the influence of ocean variability on the capacity of the Northeast Pacific to produce salmon. Bottom et al. ^{31, 32} provided information on classifications of subsystems of the Coastal Upwelling Domain.

Natural Disturbance Regime. This deeper water habitat is influenced by seasonal water temperatures, winds, currents, and upwelling. The shelf slope essentially defines the pathway of the large-scale California Current, which transports water eastward from mid-ocean, then southward to California. The current is essentially driven by seasonal northwesterly winds. The relatively wide shelf off Oregon and Washington tends to isolate the California Current and its infusion of nutrients from nearshore flow. It is pushed farther offshore during the winter when southeasterly winds generate the seasonal northern flow of the more coastal Davidson Current ¹⁴¹.

In addition to driving currents, seasonal winds also promote upwelling of colder, nutrient-rich waters. Coastal upwelling occurs most frequently in summer and fall, promoted by northerly and northwesterly winds. The upwelling season runs from April to October, with maximum intensity in July and August ¹⁸. Upwelling intensity is typically greatest along the southern Oregon coast (Cape Blanco upwelling zone) and diminishes northward. However, it can occur anywhere along the Oregon-Washington coast under favorable winds. Shelf promontories such as Heceta Bank, the submarine canyons off Washington, and the shelf edge and slope create biologically productive mixing zones influenced both by large-scale currents and upwelling. Sporadic events causing large-scale changes in both nearshore and offshore habitats include extreme La Niña (cold water) and El Niño (warm water) events, and toxic red tide blooms.

Effects of Management and Anthropogenic Impacts. The main activities in this habitat are fishing and commercial transport; other than regulations to support these actions, little active management for biological resources takes place in this habitat.