Abstract:

In September and October, 1988 a series of physical and biological observations were collected by the R/V Endeavor and R/V Cape Hatteras in a Gulf Stream meander crest. The hydrographic data and vertical chlorophyll a profiles derived from CTD/flourescence profiles (calibrated with discrete pigment samples), and zooplankton biomass (from 20m - 120m, estimated using an ADCP) are here analyzed by means of a Principle Component Analysis (PCA). The PCA of salinity, temperature, density, chlorophyll a, and zooplankton biomass were performed relative to the cross-sectional average of each. The cross-sectional average explain 80%, 80%, 54%, 50%, and 18% of the variability for density, temperature, salinity, chlorophyll a, and zooplankton biomass, respectively. The first two vertical statistical modes for both temperature and density explain almost 90% of the variability relative to the corresponding cross-sectional average, while those for salinity explain more than 80% of the detrended variability. The first two chlorophyll and zooplankton modes explain relatively less, 60% and 70%, respectively, of the detrended variability. The first vertical mode of all the physical variables were relatively coherent in the upper 100m, while that of chlorophyll a exhibited increased variability in the upper 120m with a zero-crossing at 65m. For each variable, the individual profiles were regressed onto the corresponding modes to generate a spatial/temporal series of the first two principal components for each variable. These series were analyzed in a local curvilinear coordinate system, defined by the apex of the meander crest on a daily basis. The spatial structure of the principle components for the physical variables in the curvilinear coordinate system was very similar. The temporal variability in this data set is over whelmed by the spatial variability. For all the variables, cross-stream variability dominates while there is some indication of along-stream variability, particularly in the slope water.

Reference:

Principle Component Analysis of Bio-physical Fields in a Gulf Stream Meander Crest. G.L. Hitchcock, A.J. Mariano, C.J. Ashjian, E.H. Ryan, 1994 Ocean Sciences Meeting, Eos, Transactions, AGU, 75 (3), January 18, 1994, (O11N-07).