Distribution and sources of organic biomarkers in arctic sediments from the Mackenzie River and Beaufort Shelf

Suspended sediments from the Mackenzie River Delta and surface sediments fr om the Beaufort Shelf were analyzed by alkaline CuO oxidation. In addition, elemental (percentage total organic carbon, inorganic carbon and silica) a nd stable carbon isotope compositions were determined for all samples. The carbon-normalized yields of over 60 different compounds derived from the ox idative hydrolysis of several biochemicals, including lignin, cutin, protei ns, polysaccharides and lipids were quantified and subjected to principal c omponent analyses (PCA). The results of these investigations indicate that most lignin and cutin products originate from non-woody angiosperm vascular vegetation such as that present in the tundra. For example, lignin-derived product compositions are characterized by relatively high syringyl:vanilly l and cinnamyl:vanillyl phenol ratios (exceeding 0.4 and 0.15, respectively ). The compositions of these biomarkers, especially the elevated (0.5 to 1. 5) acid:aldehyde ratios for vanillyl and syringyl phenols, also suggest tha t the land-derived organic matter (OM) exported by the Mackenzie River is h ighly degraded. Non-lignin CuO reaction products derived from proteins, pol ysaccharides and lipids display distributions that are consistent with a pr edominant marine (autochthonous) source. The composition of lipid-derived f atty acid products, which is in shelf sediments are dominated by hexanedece noic acid, suggests a planktonic origin, likely from diatoms. The distribut ion of these biomarkers across the shelf indicates the presence of relative ly fresh algal remains in at least one sample. The relationships between te rrigenous biomarker concentrations and bulk C-13/C-12 ratios in surface sed iments indicate that terrestrial organic carbon dominates in abundance (80% to 50% of total organic carbon) over much of the shelf. Marine/algal-deriv ed carbon represents 20% to 50% of the total carbon in shelf sediments, wit h the largest fraction being present in the outer mid-shelf. The large vari ability in the yields of CuO biomarkers from the river suspended sediment s amples highlights the heterogeneous nature of the particle load exported by the Mackenzie River. Such variability must be taken into account during th e development of quantitative carbon budgets for the Beaufort Shelf. (C) 20 00 Elsevier Science B.V. All rights reserved.