Acoustic observations of finescale zooplankton distributions in the Oregon upwelling region

We collected data on two GLOBEC cruises to investigate the ubiquity and character of small and finescale phytoplankton and zooplankton vertical distributions in continental shelf waters. Coincident data from a four-frequency echosounding system (38, 120, 200, and 420 kHz), CTD, 150 kHz ADCP, and a suite of high-resolution bio-optical instruments were collected at three continental shelf stations off the coast of Oregon in June and August of 2000. Temporally and spatially coherent finescale features were identified in the acoustic record at all sites throughout the upper water column and the dominant characteristics were observed. There was evidence of an association between the vertical structure of horizontal velocity and the finescale structure seen in the acoustic data. These observations support the hypothesis that discrete, finescale vertical distributions of phytoplankton and zooplankton may be common in productive upwelling areas and indicate that additional concurrent physical and biological measurements, at appropriate temporal and spatial scales, must be made to further characterize the ecological significance of these finescale distributions.