Assessment of new production at the upwelling center at Point Conception, California, using nitrate estimated from remotely sensed sea surface temperature

Abstract

Remotely sensed sea surface temperature (SST) and a model originally developed for Cap Blanc, northwest Africa [Dugdale et al., 1989], are used to estimate new production (i.e., nitrate uptake, in the sense of Dugdale and Goering [1967]) for the persistent coastal upwelling feature at Point Conception, California. Parameters required to initialize the model and remotely sensed SST (from advanced very high resolution radiometer images) were available for spring 1983, from data collected as part of the Organization of Persistent Upwelling Structures (OPUS) study. Some examples of the spatial extent of new production are illustrated using false color images, and temporal variability is shown by the time series of depth‐ and area‐integrated nitrate uptake obtained from eight images. The model results are compared with shipboard data for three different upwelling conditions that occurred during OPUS‐83, along with the model results and data published for Cap Blanc. These two regions, Point Conception and Cap Blanc, represent two ends of a spectrum of coastal upwelling performance, with low new production at Point Conception and less effective conversion of available nitrate into particulate nitrogen biomass in contrast to the high levels of new production at Cap Blanc. The daily new production at the Point Conception upwelling center is about 10% of the Cap Blanc new production, both estimated from the remote‐sensing model and satellite‐derived SSTs. The model is shown to work well for both extremes and should therefore be suitable for intermediate situations. The long‐term objective is to produce a model which can be used for coastal upwelling systems globally to provide a estimate of new production from remotely sensed data in these important areas and to assist in understanding the role of these coastal systems in the air‐sea exchange of biogeochemical elements.