Organic Geochemistry in Particulate Matter in the Eastern Tropical North Pacific Ocean: Implications for Particle Dynamics

摘要

Samples of marine particulate matter were collected in sediment traps and by in-situ filtration to depths of 1500 m during VERTEX II and III cruises in the eastern tropical North Pacific. Wax esters, triacylglycerols, fatty acids, sterols and steroidal ketones were analyzed in these samples to compare the compositions of organic matter associated with large sinking particulate aggregates sampled by sediment traps and with fine suspended material obtained by in-situ filtration. Distributions of specific compounds indicated that the organic chemical composition of large sinking particles and small suspended particles both in the euphotic zone and at mid-depth result from very distinct particle pools, not only in terms of particle size but also in their sources and transport mechanisms. Suspended particles in the epipelagic zone contain a mix of organic compounds derived from both phytoplankton and zooplankton sources, whereas sinking particles are dominated by zooplankton-derived compounds. In the mesopelagic zone, large sinking particles contain organic compounds which are indicative of intensive alteration of organic matter, even though transport from the euphotic zone may have been rapid. On the other hand, it is the suspended particle pool which contains a remarkable abundance of labile organic compounds which can be attributed to undegraded phytoplankton cells rapidly delivered from surface waters. These organic geochemical results lead to a modified model of particle dynamics in which there are two distinct large, sinking particle pools which are differently sampled by the two sampling techniques. Reprints. (mjm)