Abstract
An unanticipated observation during the Coastal Transition Zone (CTZ) experiment is the occurrence of layers of high concentrations of phytoplankton at depths often greatly exceeding the euphotic zone. These layers are found both near shore and offshore within a productive coastal upwelling system off northern California and are often observed in a strong offshore jet that was present in the CTZ study area in 1988. We explore the hypothesis that the water masses associated with these layers originate near the surface in the euphotic zone and are subsequently transported downward by vertical circulation processes or subduction (other terms such as subsidence or downdwelling are equally descriptive). The subduction hypothesis is supported by a variety of physical, biological, and geochemical indicators.
Prepared in cooperation with Oregon State Univ, Corvallis, College of Oceanography, and Scripps Institution of Oceanography, La Jolla, CA.