The Maine Coastal Current’s Role in the Movement of the Fall Algal Bloom

In the Gulf of Maine, the dominant near-shore current system is the Maine Coastal Current (MCC), a bathymetrically constrained buoyancy current running from Nova Scotia to Cape Cod. The two constituent branches, the Eastern Maine Coastal Current (EMCC) and Western Maine Coastal Current (WMCC) meet off Penobscot Bay, where they connect or recirculate, for reasons still not fully understood. When they connect, the MCC can be viewed as one coherent current, flowing alongshore in a generally southwesterly direction. The fall algal bloom in the Gulf of Maine, generally thought to be driven by autumnal cooling and convective mixing, also propagates along the coast in a southwesterly direction following the path of overturn. Here, we use fifteen years of measurements of ADCP velocities, hydrographic data, and chlorophyll fluorescence from four locations along the coast of the Gulf of Maine to demonstrate that the observed propagation of the fall algal bloom, in the same direction as the MCC, is not due to advection, but is likely entirely driven by convection. The data exhibit a fall shutdown of the alongshore component of the WMCC off Massachusetts, occurring comtemporaneously as the fall algal bloom propagates southward. Interannual anomalies in current velocity and chlorophyll also show no coherence. By presenting new observations of the Maine Coastal Current and the coastal dynamics of the Gulf of Maine, we hope to further the general understanding of primary productivity and dynamics in this complex marginal sea.