TRAPPED, NEAR-INERTIAL WAVES AND ENHANCED CHLOROPHYLL DISTRIBUTIONS

Waves with near-inertial frequencies were observed along a front assoc iated with a large mesoscale feature in the Sargasso Sea during the la te summer of 1987. High subsurface chlorophyl concentrations occurred on the edge of this front, coincident with the wave packets, The ampli tude of the waves increased with time, and kinetic energy propagated d ownward, reducing 20-m Richardson numbers in the thermocline to 1 or l ess. Chlorophyll levels were episodic, showing no periodicity coincide nt with wave dynamics, However, on two occasions, chlorophyll concentr ation increased from <0.5 to >1 mg Chl m(-3), several hours after the waves penetrated the thermocline. It was hypothesized that mixing asso ciated with shear instabilities stimulated new production, A diffusivi ty model combined with nutrient data produced a phytoplankton bloom th at accounted for only one of the maxima, The other increase in chlorop hyll may have been the result of horizontal advection of the wave pack ets near the front.