COMPOSITIONS AND TRANSPORT OF LIPID BIOMARKERS THROUGH THE WATER COLUMN AND SURFICIAL SEDIMENTS OF THE EQUATORIAL PACIFIC-OCEAN

A systematic investigation of fluxes and compositions of lipids throug h the water column and into sediments was conducted along the U.S. JGO FS EqPac transect from 12 degrees N to 15 degrees S at 140 degrees W. Fluxes of lipids out of the euphotic zone varied spatially and tempora lly, ranging from approximate to 0.2-0.6 mmol lipid-C m(-2) day(-1). L ipid fluxes were greatly attenuated with increasing water column depth , dropping to approximate to 0.002-0.06 mmol lipid-C m(-2) day(-1) in deep-water sediment traps. Sediment accumulation rates for lipids were =0.0002-0.00003 mmol lipid-C m(-2) day(-1). Lipids comprised approxim ate to 11-23% of C-org in net-plankton, 10-30% in particles exiting th e euphotic zone, 2-4% particles in the deep EqPac, and 0.1-1% in sedim ents. Lipids were, in general, selectively lost due to their greater r eactivity relative to bulk organic matter toward biogeochemical degrad ation in the water column and sediment. Qualitative changes in lipid c ompositions through the water column and into sediments are consistent with the reactive nature of lipids. Fatty acids were the most labile compounds, with polyunsaturated fatty acids (PUFAs) being quickly lost from particles. Branched-chain C-15 and C-17 fatty acids increased in relative abundance as particulate matter sank and was incorporated in to the sediment, indicating inputs of organic matter from bacteria. Lo ng-chain C-37-C-39 alkenones of marine origin and long-chain C-20-C-30 fatty acids, alcohols and hydrocarbons derived from land plants were selectively preserved in sediments. Compositional changes over time an d space demonstrate the dynamic range of reactivities among individual biomarker compounds, and hence of organic matter as a whole. A thorou gh understanding of biogeochemical reprocessing of organic matter in t he oceanic water column and sediments is, thus, essential for using th e sediment record for reconstructing past oceanic environments. (C) 19 98 Elsevier Science Ltd. All rights reserved.