COMPARISON OF PELAGIC AND NEPHELOID LAYER MARINE SNOW - IMPLICATIONS FOR CARBON CYCLING

Marine snow from upper and mid-water (i.e., pelagic) depths on the Cal ifornia margin is texturally and compositionally different from that t raveling in the nepheloid layer. Transmission electron microscopy show s that pelagic marine snow consists primarily of bioclasts (e.g., diat om frustules, foram tests), organic matter, and microbes. These compon ents are entrained as discrete particles or small aggregates (less tha n or equal to 10 mu m in diameter) in a loose network of exocellular, muco-polysaccharide material. Clays are infrequent but, when present, are constituents of comparatively compact organic-rich microaggregates . Microbes are abundant and appear to decrease in number with increasi ng water depth. In contrast, marine snow aggregates collected from jus t above the sea floor in the nepheloid layer are assemblages of clay p articles, clay flocs, and relatively dense clay-organic-rich microaggr egates in an exocellular organic matrix. Bioclasts and microorganisms occur only rarely. The prevalence of clay-organic-rich aggregates in t he nepheloid layer suggests that, prior to final deposition and burial , marine snow from the pelagic zone is subject to disaggregation and r ecombination with terrigenous detrital material near or at the sea flo or. Results have significant implications for the accumulation and bur ial rates of organic carbon on continental margins and the aging and b ioavailability of sedimentary organic matter. Samples examined were co llected offshore of northern and central California. (C) 1998 Elsevier Science B.V. All rights reserved.