BIOGEOCHEMISTRY OF ORGANIC-MATTER IN THE LAURENTIAN TROUGH .1. COMPOSITION AND VERTICAL FLUXES OF RAPIDLY SETTLING PARTICLES

Settling particles from duplicate free-drifting sediment traps were co llected at 150 m depth in May and July at a landward and a seaward sit e in the 350 m deep Laurentian Trough. The total organic carbon (TOC) fluxes were high (95-454 mg/m(2)/d), comparable to those reported for Dabob Bay (a similar moderately productive deep coastal environment) a nd for the highly productive Peru upwelling region. The TOC (26-67 mg C/g) consisted of lipids (17-37%), carbohydrates (7.9-16%), hydrolysab le amino acids (8.4-16%), labile proteins (0.3-2.6%), and a non-charac terized fraction (40-64%). Amino acids, proteins and uncharacterized c ompounds accounted for 24-42, 1-10 and 58-76%, respectively, of total nitrogen (2.3-7.7 mg N/g). The pigment fraction was largely dominated by pheopigments (0.06-1.15 mg/g vs 0.004-0.15 mg/g for chlorophyll a). C/N and C/pigment ratios indicated that on average, about half of the carbon flux was of terrigenous origin. Marine sources included a domi nant zooplanktonic contribution, indicated by the abundance of fecal p ellets, lipids and pheopigments, and a smaller contribution from fresh algae. Cluster and correlation analyses confirmed the decoupling of p igment and TOC fluxes and the strong zooplanktonic influence of the tr ap material. Despite large day-to-day and inter-trap variability, clea r differences were observed in the fluxes, TOC content and composition at both sampling sites and months. Such trends are attributed to the relative contribution from terrestrial and marine sources and seasonal patterns of primary production.