THE EFFECT OF GRAIN-SIZE AND SURFACE-AREA ON ORGANIC-MATTER, LIGNIN AND CARBOHYDRATE CONCENTRATION, AND MOLECULAR COMPOSITIONS IN PERU MARGIN SEDIMENTS

A C-rich sediment sample from the Peru Margin was sorted into nine hyd rodynamically-determined grain size fractions to explore the effect of grain size distribution and sediment surface area on organic matter c ontent and composition. The neutral monomeric carbohydrate composition , lignin oxidation product yields, total organic carbon, and total nit rogen contents were determined independently for each size fraction, i n addition to sediment surface area and abundance of biogenic opal. Th e percent organic carbon and percent total nitrogen were strongly rela ted to surface area in these sediments. In turn, the distribution of s urface area closely followed mass distribution among the textural size classes, suggesting hydrodynamic controls on grain size also control organic carbon content. Nevertheless, organic compositional distinctio ns were observed between textural size classes. Total neutral carbohyd rate yields in the Peru Margin sediments were found to closely paralle l trends in total organic carbon, increasing in abundance among grain size fractions in proportion to sediment surface area. Coincident with the increases in absolute abundance, rhamnose and mannose increased a s a fraction of the total carbohydrate yield in concert with surface a rea, indicating these monomers were preferentially represented in carb ohydrates associated with surfaces. Lignin oxidation product yields va ried with surface area when normalized to organic carbon, suggesting t hat the terrestrially-derived component may be diluted by sorption of marine derived material. Lignin-based parameters suggest a separate so urce for terrestrially derived material associated with sand-size mate rial as opposed to that associated with silts and clays. Copyright (C) 1997 Elsevier Science Ltd.