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The aim of this proposal is to explore, using a coupled biological-physical model, how remote, climate-based forcings interact with local forcings to impact phytoplankton blooms in coastal and shelf regions. Phytoplankton bloom dynamics are perhaps the classic example of biological-physical interactions in the ocean, and they have attracted considerable attention by researchers ever since the early theories of Gran and Braarud (1935) and Sverdrup (1953).  Yet the key challenge remains to identify the dominant processes controlling the interannual variability of phytoplankton blooms in coastal and shelf seas where multiple-scale biological and physical processes interact.  We believe that a major difficulty lies in the integration of processes and forcings that operate on vastly different time and space scales. Built on successes in interdisciplinary measurements and modeling during the GLOBEC Georges Bank Program, the unstructured-grid, finite-volume, coastal ocean model (FVCOM) has bridged the broad gap in multi-scale physical processes in the Gulf of Maine by encompassing both local and remote forcings.  Thus far, 12 years of prognostic simulation and assimilation experiment products, with careful comparison/validation with field measurements, have provided us a unique background and tools with which to explore the interannual variability of ecosystem dynamics in coastal shelf regions such as the Gulf of Maine.  We propose to examine relationships between phytoplankton bloom dynamics in the Gulf (including both spring and fall blooms) and local and remote forcings, with specific focus on the importance of variability in inflows of Scotian Shelf Water and Slope Water to the system.  A series of numerical experiments will be conducted to test long-standing and newly-proposed hypotheses, including those that address the likely impact of the North Atlantic Oscillation as it influences Warm Slope Water versus Labrador Slope Water dynamics, which in turn affect nutrient fluxes to the Gulf of Maine and vertical fluxes between surface and deep waters.  We will also address influences of surface water freshening (related to Scotian Shelf Water inflow, which is in turn believed to be affected by global warming) on the vertical density structure of the water column, winter convection, and consequently, the timing/magnitude of blooms. The process-oriented coupled biological and physical model experiments will focus on the date-rich period 1998-2001 when pronounced large-scale forcing conditions occurred.


  This project is funded by NSF Biological Oceanography Division


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