The principal objective was simultaneous assessment of the transport of water and plankton in the vicinity of the tidal mixing front. The approach was to inject Rhodamine dye into specific density strata and then measure the movement of the dye patch and the associated planktonic community with respect to the neighboring front. This was accomplished through incorporation of the fluorometric dye detector into the Video Plankton Recorder system, facilitating real-time assessment of both tracer and plankton distributions (down to the species level). The adjacent waters were also seeded with radio- and satellite-tracked drifters. Real-time data assimilative modeling of the flow field (and associated transports of tracer and plankton) was carried out in concert with the observational activities, in order to (1) provide an additional interpretive framework for the measurements, and (2) provide nowcast/forecast products which could be used in planning sampling strategy.
Skill of the model predictions was evaluated against observed drifter trajectories. In aggregate, the error growth characteristics of the ensemble of "best" model forecasts were surprisingly uniform. For the four-day time horizon over which forecast skill was evaluated in the various experiments, forecast error was a linear function of the duration of the prediction. On average, separation between simulated and observed trajectories of drifters and dye grew at a rate of 3 km/day. This error growth rate is small given the physical context of order 100 cm/sec tides and 10-30 cm/sec residual flows in this region.
While at sea, model solutions were used as a basis for data-assimilative coupled physical/biological simulations. Observed distributions of Calanus finmarchicus and hydroid predators were assimilated into the modeled flow fields in order to assess their relative transports and interactions. Coupled simulations revealed portions of overlap in the sampling coverage due to the configuration of the survey track and phasing with the tide. Relative motion between predator and prey was apparent due to the vertical separation of the two populations in the presence of shear.