Theses and Dissertations

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Defense Date

1995

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Ocean Science

Department

Oceanographic Center

First Advisor

Gary S. Kleppel

Second Advisor

Barry Klinger

Third Advisor

William Venezia

Abstract

Time series of zooplankton concentrations and current velocities were collected with a bottom mounted (190 m) 307.2 kHz acoustic Doppler current profiler (ADCP) at the shelf break off Fort Lauderdale, Florida. Simultaneously, time series of temperature and salinity were collected with a moored CTD in the Port Everglades estuary approximately 4 km inshore of the ADCP mooring. Software was developed to extract acoustic volume scattering strength data (Vs) from the ADCP data stream. Vs is a relative measure of zooplankton concentration. In addition, eastward velocity and northward velocity data were collected from the ADCP. Data were recorded in two minute averages, with additional processing yielding hourly averages. Acoustic volume scattering strength and current velocity records from 176, 136, 95, and 56 m deep were isolated during post-processing for spectral analysis. The acoustic estimate of zooplankton concentration was found to be coherent with current velocity (both north and east components) at frequencies corresponding to the scales of Gulf Stream meanders (2-10 days per cycle) and diurnal and semi-diurnal tidal variability (24 and 12 hours per cycle, respectively). Estuarine salinity variations were also coherent with variability in circulation at the shelf break at the energetic periods of 24, 12, 8 and 6 hours per cycle. Estuarine salinity varied inversely with the distance of the Gulf Stream front from shore (0.5 - 6 week observation interval). Apparently, low frequency variability in the salinity of estuarine water is also associated with variability in the position of the Gulf Stream. It would appear that variability of Gulf Stream position and flow influences the cross-shelf transport of planktonic organisms, such as fish larvae, at a variety of temporal scales and thereby links offshore and estuarine ecosystems off southeast Florida.

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