Multi-sensor and Modeling Analysis of Gulf of Maine Phytoplankton Variability

Multiple satellite sensors and a coupled biological-physical numerical model will be used to quantify interactions between physical forcing and biological response in the greater Gulf of Maine region. Our focus is on chlorophyll and primary productivity variability estimated with NASA's ocean color missions. Overall goals are: 1) quantify the spatial and temporal variability of physical forcing, hydrography, phytoplankton biomass and primary productivity in the greater Gulf of Maine system, 2) separate local from non-local forcing, and quantify the linkage of each to variability in phytoplankton dynamics, 3) isolate and quantify regional differences in phytoplankton variability within the Gulf of Maine system, showing downstream effects and linkages. Reprocessed SeaWiFS data will provide 3-6 years of ocean color data over the life of the project. MODIS color and temperature data provide improved separation of phytoplankton and other color constituents as well as estimates of primary productivity. These data will be supported by concurrent NOAA AVHRR SST and QuikSCAT wind fields. A 12 year time series of PATHFINDER SST for the Gulf of Maine will establish climatological patterns and variability statistics. Our analysis is based on statistical examination of these satellite data time series. Our modeling will allow examination of sensitivity and response to specific forcing events including such climate-change related metrics as the North Atlantic Oscillation, Gulf Stream position, slopewater intrusions and Scotian Shelf variability. The biochemical part of our numerical model is a 10 component N-P-Z model with two size classes each of phytoplankton and zooplankton. These allow us to generate space / time fields, separate new from total production and make distinctions between diatom and flagellate community response and productivity. This biochemical model is coupled with an implementation of the Princeton Ocean Model (POM) on a 151x103 grid with 19 vertical levels, providing complete circulation and hydrography in our study domain. Extensive in situ data sets, both retrospective and concurrent with the proposed project, from (separately funded) field surveys, buoy arrays and CODAR installations provide superb ground truth for both the forcing and biological aspects of the research proposed here.


The Gulf of Maine is uniquely suited to this type of study. A highly productive marginal sea, it showcases strong gradients in hydrography, direct connections to both NW Atlantic basin-scale processes and non-local shelf processes, and an overall cyclonic circulation which delivers both forcing and biochemical signals to downstream subregions. In addition, there is strong spatial heterogeneity within the Gulf in both bathymetry and physical forcing, resulting in contrasting time / space patterns of circulation and hydrography. Two specific examples of the regionality we will use as a testbed for bio-physical linkages include i) the large east-west gradient in tidal amplitude and resultant mixing/stratification and ii) bathymetry, which contrasts the circulation / hydrography / phytoplankton ecology of shallow banks with that of deep basins. Biological responses to this heterogeneity are equally strong, with distinct regionality in such characteristics as phytoplankton biomass, community structure, new and total primary productivity and the timing and magnitude of each on event, seasonal and interannual scales. These make the Gulf of Maine an excellent laboratory within which to examine linkages both between physical forcing and biological response and also between open ocean and shelf/coastal variability. Indeed, the time and space heterogeneity of the study domain is such that numerical modeling and satellite data are the only realistic approach to understanding the functioning of the system as a whole.