Evaluation and application of satellite primary production models in Massachusetts Bay

A variant of the Vertically Generalized Production Model (VGPM) was used to expand the spatial and temporal resolution of production estimates and better characterize the phytoplankton variability in Massachusetts and Cape Cod Bays. Satellite modeled production was used to supplement in situ 14C primary production measurements, which were spatially limited to two shipboard stations in the northern portion of Massachusetts Bay that were sampled up to 17 times per year. Modifications to the model included a regional parameterization of the euphotic depth (Zeu) and an analysis of the maximum chlorophyll specific carbon fixation rate (Poptb), which failed to reveal a correlation between Poptb and temperature as suggested by previous studies. This primary production model successfully captured the seasonal and interannual variations of in situ production that were measured using the 14C uptake method and significantly enhanced the spatial and temporal resolution of primary production measurements in Massachusetts Bay. The use of satellite data better characterized event, seasonal and interannual variability of ecosystem primary production and revealed a three-fold decrease in production from the nearshore to offshore regions. Daily production ranged from less than 0.25 g C m−2 d−1 in the offshore regions in January to greater than 2 g C m−2 d−1 at various times throughout the year in Cape Cod Bay and along the coastline during the summer months. The mean annual production of Massachusetts Bay for the 8-year study period was 220 g C m−2. The lowest production was estimated in 2004 (174 g C m−2) and the greatest in 2000 (300 g C m−2). Comparatively, mean production in Cape Cod Bay was 289 g C m−2 and ranged from 231 in 1998 to 358 g C m−2 in 2000. Unlike a number of other temperate continental shelf areas where the maximum production occurs during the summer months corresponding to the greatest PAR and temperature, the highest production and largest fraction of the annual production in Massachusetts Bay accompanied the high phytoplankton biomass during the spring (April-May) and fall blooms (September-October).