A CLASSIFICATION SCHEME FOR MARINE ORGANIC COLLOIDS IN THE ADRIATIC SEA - COLLOID SPECIATION BY TRANSMISSION ELECTRON-MICROSCOPY

Organic colloids from the Adriatic Sea, covering the full colloid size range, were characterized on a per-colloid basis by transmission elec tron microscopy applied to ultrathin sections of embedded colloids. To detect, assess, and minimize artifacts, a multimethod correlative app roach to analysis was used. A colloid classification scheme was develo ped from the characterizations, with individual colloid species define d in the broad sense established by environmental analytical aquatic c hemists. The basic scheme is related to derivative classification sche mes in which abundant colloid species are listed according to activiti es known from the literature, with a focus on activities related to ca rbon transformations and transport. Morphological criteria show that a bundant colloid species occupy broad size ranges, such that colloid fr actionation protocols based on sizing alone are likely to be of questi onable scientific utility. Image analysis revealed that small colloids , designated as humic substances, represented 91% of the total organic colloid burden of the bulk water during a summer period of high biolo gical productivity. At this time, fibrils were rare in the bulk water while representing the most abundant colloid in marine snow.