Interannual and seasonal phytoplankton variability in Massachusetts Bay from remote and in situ measurements

This study investigated the feasibility of augmenting monitoring data collected in Massachusetts Bay with satellite ocean color data to increase the spatial and temporal resolution of quantitative phytoplankton measurements. In coastal regions such as Massachusetts Bay ocean color remote sensing can be complicated by in-water constituents whose quantities vary independently of phytoplankton and by inaccurate modeling of absorbing aerosols. An evaluation of in situ and SeaWiFS measurements demonstrated that SeaWiFS overestimated chlorophyll a mainly due to atmospheric correction errors that were amplified by absorption from elevated concentrations of chlorophyll a and color dissolved organic matter. A regional empirical algorithm was developed to correct the SeaWiFS data. The corrected SeaWiFS chlorophyll product was incorporated into a remote sensing primary productivity model that was developed from in situ 14Carbon productivity measurements. The Vertically Generalized Massachusetts Bay (VGMB) model, expanded the predictability of primary productivity throughout the Massachusetts Bay region. The VGMB successfully captured the seasonal and interannual variations in productivity that were observed by 14C measurements and significantly enhanced the spatial and temporal resolution when combined with SeaWiFS imagery. SeaWiFS chlorophyll a and modeled productivity were used in conjunction with in situ measured physical, chemical and biological data to quantify the spatial, seasonal, and interannual phytoplankton variability. Monthly composites illustrated the spatial extent of a bimodal seasonal pattern and revealed interannual variations in the location, timing, magnitude and duration of phytoplankton blooms. Spatially, there was an onshore to offshore gradient of mean production and biomass that decreased with increasing depth. Spatial heterogeneity of event scale changes in phytoplankton abundance and productivity was generally in response to changes in local winds, buoyancy forcings and run-off events. Large interannual differences of the winter-spring bloom were observed in all regions, while episodic summer blooms were typically isolated to the northern and western shore regions. Despite known artifacts of SeaWiFS in coastal regions, this study provided viable chlorophyll a and primary productivity products in Massachusetts Bay that significantly increased the spatial and temporal synoptic coverage of phytoplankton dynamics, which was used to gain a comprehensive ecosystem-wide understanding of phytoplankton dynamics at various timescales.