| High vertical and temporal resolution observations of currents and hydrography were used to investigate the variable influences of internal solitary and tidal waves on turbulence, vertical mixing and effects on biological processes in the stratified western Gulf of Maine during 1995--1996. Tidally-generated solitons are characterized by mean amplitudes of 10 m, half-widths of 400 m, and periods of 7.5 min. Wave packets generated on flooding phases of the surface tide at Georges Bank consist of 6--10 coastward propagating solitons. An unexpected secondary set of 2--4 solitons propagate seaward on ebbing tides, shed by critically sloping topographic features located shoreward of the mooring site. The vertical EOF structure of both wave groups included significant first and second modes. Kinematic properties of both wave groups were statistically similar and compared favorably to KdV theory. Approximately ¼--½ of internal tidal energy is partitioned into the solitary wave groups, depending on year and stratification.; Strong solitary internal wave were observed to dramatically increase turbulence and vertical diffusivity. Mean diffusivity in the pycnocline was O(10-5 m2 s-1), and enhanced ten-fold by large amplitude solitary waves with strong vertical shear. A mean daily vertical flux nitrate flux was 23--12.1 x 10 -3 g N m-2 d-1. Statistics of soliton occurrence suggest that an average of 50% of the daily flux is delivered in rapid, episodic bursts occurring less than 3% of the time. Internal solitary wave-enhanced fluxes account for 0.5--2% of total annual nitrate flux to the Gulf s euphotic zone.; The arrival of Hurricane Edouard in September 1996 eroded stratification, damping internal solitary waves and initiating a strong internal inertial response. Inertial-band vertical shear drove strong interfacial mixing, deepening the pycnocline after storm winds decayed. Interference with the internal tide apparently modulated the vertical shear. A post-storm survey revealed elevated nutrient concentrations in the euphotic layer and a doubling of in-situ chlorophyll biomass. Primary productivity was curtailed following depletion of surface inorganic nutrients and decay of inertial currents. This highlights the role of inertial response as a transient agent of nutrient supply in relatively deep, well-stratified coastal regions. |
