A predictive model for estimating rates of primary production in the subtropical North Pacific Ocean

Abstract

Abstract A primary production model, specific to the subtropical North Pacific, was developed using productivity and chlorophyll data collected at Station ALOHA (22.75°N, 158.00°W) and measured phytoplankton physiological parameters. The production algorithm is a mechanistic, full spectral model that provides depth-dependent photosynthesis rates. Six years of phytoplankton pigment data were analyzed to derive seasonal cycles and to parameterize chlorophyll a (Chl; monovinyl and divinyl chlorophyll a) versus depth profiles. The Chl profiles fit a Gaussian-type distribution with depth over a constant background concentration equal to mixed-layer values. Maximum Chl concentrations were always found below the surface, and the parameters displayed distinct monthly and seasonal patterns. Photosynthesis versus irradiance experiments were conducted at a number of locations and seasons in the vicinity of Station ALOHA to calculate phytoplankton physiological parameters needed for the computation of primary production rates. Relationships were explored between environmental conditions and the physiological and profile parameters in order to develop algorithms based on remotely sensed sea-surface variables and time of year. These relationships were used to model primary production rates using data collected during the Hawaii Ocean Time-series (HOT) program. The performance of the model and model parameters were tested by comparing modeled results to those measured directly at Station ALOHA by trace metal-clean, in situ 14C incubation techniques. Monthly averaged chlorophyll profile parameters and a constant maximum quantum yield (0.026 mol C(mol quanta)−1) generates an annual production estimate of 168 g C m−2, which closely resembles that measured at Station ALOHA (181 g C m−2) during the same period. The measured and modeled primary production rates for the subtropical North Pacific are twice as high as values derived from Coastal Zone Color Scanner (CZCS) data (60–90 g C m−2) during the period 1978–1986. If the study area near Station ALOHA is representative of most oligotrophic waters, current global estimates of primary production rates have been significantly underestimated.