PROCESSES CONTRIBUTING TO THE NUTRIENT DISTRIBUTION OFF THE COLUMBIA RIVER AND STRAIT OF JUAN DE FUCA1

Abstract

Listen

Translate article

The distribution of salinity, dissolved oxygen, silicate, nitrate, and phosphate off the Washington and Oregon coasts, both inside and outside the Columbia River plume, were observed during 12 cruises of the RV Brown Bear between January 1961 and April 1962.Nutrients are supplied to the surface waters off the Washington and Oregon coasts from rivers and from the deeper layers of the ocean. The deep water enters the surface layers by entrainment, especially in the estuarine‐like circulation in the Strait of Juan de Fuca; by upwelling, particularly off the Oregon coast in summer; and by upward mixing into the photic zone.The most important river source of nutrients is the Columbia River, which supplies high concentrations of phosphate and nitrate to its “plume,” those waters appreciably diluted by its admixture.In winter, the plume waters are approximately simple mixtures of Columbia River and surface seawater, and their silicate and nitrate concentrations can be predicted from the salinity. In the spring and summer, nutrients are also added by the admixture of upwelled deep water and removed by photosynthetic fixation. The amounts thus added or removed have been estimated as departures, or anomalies, from the composition of simple mixtures of river and surface seawaters. These anomalies are compared with each other, with the average composition of plankton material, and with other evidences of biological activity, both in terms of correlations with each other and of horizontal distributions in the upper 10 m.