THE VARIABILITY OF SUSPENDED AGGREGATES ON THE AMAZON CONTINENTAL-SHELF

Underwater photographs taken as part of the AmasSeds project from 1989 to 1992 reveal the abundance of suspended aggregates on the Amazon Co ntinental Shelf. Computerized image analysis of photographs from speci fic layers within the water column at inner shelf, midshelf, outer she lf, and rivermouth anchor stations allowed description of the in situ characteristics of the aggregates, or flocs. Flee sizes varied from th e lower limit of detection (125 mu m) to a maximum greater than 2 mm, with a mean diameter of 518 mu m and a modal diameter of 646 mu m for the complete data set. Additionally, large, elongate, comet-shaped agg regates (stringers) as large as 2.5 cm were observed in individual pho tographs. Results of hoc-size analyses (in terms of the maximum hoc si ze, d(MAX)) were compared to salinity, particle concentration, and cur rent velocity. Additionally, d(MAX) was also compared to shear (G) and the Kolmogorov microscale (lambda). Results suggest that salinity has little effect on d(MAX) (r(2) = 0.06), while particle volume concentr ation demonstrates a strong relationship with d(MAX) (r(2) = 0.92). Th e maximum flee size increased with increased current velocity and G up to a critical value (flee growth stage) and then decreased as the cur rent velocity and G continued to increase (flee breakup stage). The Ko lmogorov microscale, which describes the size of the smallest turbulen t eddies (and, thus, should limit the d(MAX) observed) also demonstrat es a relationship with the observed maximum flee size. The results sug gest that d(MAX) is approximately one-half the magnitude of the Kolmog orov microscale (lambda). Copyright (C) 1996 Elsevier Science Ltd