Effects of Solar Radiation and Upwelling on Daily Primary Production off Oregon

Abstract

Primary production was measured in units of gC m−2 day−1 (=P) and gC (gChla)−1 day−1 on a per meter squared basis (=PChl) for 4 years in Oregon coastal waters and offshore areas. P, and particularly PChl, were functions of daily photosynthetically usable radiation inshore except in summer, and offshore apparently during all seasons. Values of P and PChl for a given daily input of usable radiation were higher inshore than offshore, probably because of more efficient use of penetrating light by the relatively heavy coastal phytoplankton populations in nutrient-rich water. Evidence is presented that inshore phytoplankton populations in winter are acclimated to low light relative to inshore populations in spring.P and PChl are related to the interaction of daily radiation and degree of upwelling in Oregon coastal waters in summer. P is a function of photic depth offshore and inshore, except in summer. Probably the presence of large quantities of non-photosynthesizing detritus, even in areas of upwelling, destroys the relation in summer. There apparently is no simple relation involving daily production and certain significant environmental factors which will allow prediction of daily production in all regions of the ocean during all seasons.