Controls on the organic chemical composition of settling particles in the Northeast Atlantic Ocean

The organic matter of sinking particulate material collected in the Northeast Atlantic Ocean (ca. 49 degreesN, 16 degreesW) was investigated in order to determine temporal and depth-related variability in its composition. Three sediment traps were deployed at nominal depths of 1000 m (below the permanent thermocline), 3000 rn (representing the deep-water fluxes) and at 4700 m, about 100 m above the seafloor Oust above the benthic boundary layer). The samples span a 28-month sampling period from October 1995 until February 1998, each sample representing a period of between 7 and 28 days. Total organic carbon and total nitrogen contents decrease with depth, as did the absolute concentrations of most biochemicals measured in this study, such as intact proteins and individual lipids. However, concentrations of proteins relative to total organic carbon and total nitrogen did not show any significant change with depth, implying that they are not being rapidly degraded and so may provide an important supply of nitrogen to the benthos. Fluxes of protein, TN and TOC are significantly correlated at all depths. Lipid compositions vary temporally. During periods of high flux, particularly in the summer, the lipids are richer in 'labile components', namely unsaturated fatty acids and low molecular weight alcohols. During periods of low flux other compounds, such as sterols, steroidal ketones and a trisnorhopan-21-one are more abundant. One sample, taken close to the seafloor, was highly enriched in lipids, sterols and fatty acids in particular; this may represent detritus derived from bottom-dwelling invertebrates. (C) 2001 Elsevier Science Ltd. All rights reserved.