Organic matter from a sediment trap experiment in the equatorial north Atlantic: wax esters, steryl esters, triacylglycerols and alkyldiacylglycerols

Abstract

The vertical flux and composition of wax esters, steryl esters, triacylglycerols, and alkyldiacylglycerols in particulate matter was determined in the equatorial Atlantic Ocean by deploying sediment traps at 389, 988, 3,755 and 5,068 m. Detailed compositional analyses of these lipids were carried out by high temperature glass capillary gas chromatography and gas chromatography/mass spectrometry. The distributions of these lipids are discussed in terms of potential biological sources. Zooplankton fecal matter and intact zooplankters may represent the most important input of these compounds to the shallower two traps, while the material in the deeper two traps appears to have been biogeochemically altered. The finding of these biochemically important compounds, often unsaturated, indicates that particle transit through the water column must be relatively fast. Wax esters were most abundant in the 389 m sediment trap and decreased with increasing trap depth. Compounds ranging from C 28–C 44 were present at all depths. The major homologs were C 32, C 34 and C 36, most often monounsaturated. The dominant alcohol/acid combinations in the 389 m trap were C 18:1 C 14:0 and C 18:1 C 16:0 , but in the 988 m sample, C 16:0 C 18:1 was the major wax ester. A flux maximum was observed for steryl esters at 988 m. Cholesteryl esters of C 14:0, C 16:1 and C 16:0, and C 18:1 C 18:0 fatty acids were the dominant steryl esters. For triacylglycerols, fluxes in the 389 and 988 m traps were similar, while the deeper pair of traps contained much less triacylglycerol. C 46, C 48, C 50 and C 52 compounds were the major triacylglycerols. Constituent fatty acids in the 389 m and 988 m samples were mainly C 14:0, C 16:1, C 16:0, C 18:1 and C 18:0. In the 988 m material, C 20:5 and C 22:6 were also dominant. A homologous series of alkyldiacylglycerols was abundant in the 389 m trap material. The alkyldiacylglycerols consisted of C 46–C 56 compounds composed of C 16:0 alkyl moieties and C 14:0, C 16:0, C 18:1, and C 18:0 fatty acids.