The biogeochemistry of particulate lipids in warm-core Gulf Stream ring systems. (Volumes I and II)

The particulate organic carbon (POC) cycle in the upper 1000 m was investigated in two warm-core Gulf Stream rings, and the surrounding Slope Water, Gulf Stream and Sargasso Sea using fatty acids and lipid classes as tracers of sources and transport/transformation pathways. The {dollar}omega{dollar}3 fatty acid isomers ({dollar}omega{dollar}3 PUFAs), labile phytoplankton-synthesized compounds bioaccumulated by animals, were used to trace the fate of labile surface-derived compounds involved in biological cycles. Suspended POC reflected the balance of short-term biological processes in the water column. The results indicate the major role of zooplankton in transport and transformation processes.; An incubation experiment demonstrated that suspended particulate fatty acids can turn over rapidly due to associated microbial activities, resulting in rapid {dollar}omega{dollar}3 PUFA losses and ingrowth of bacterial acids. However, suspended particulate fatty acids throughout the water column were characteristic of eucaryotic sources with relatively high levels of labile {dollar}omega{dollar}3 PUFAs, indicating a high rate of input of labile material into the suspended particle pool. In the euphotic zone, suspended fatty acids reflected the variability of autotrophic sources. Prior to seasonal stratification, deep convective mixing rapidly transported surface material to depths of 400 m. Following stratification, zooplankton-derived products, rather than sinking and breakup of surface-derived phytoplankton aggregates, were the major source of labile suspended particulate lipids below the seasonal thermocline.; Zooplankton grazing and bioassimilation played a major role in transport and transformation pathways. Large particles were greatly depleted in {dollar}omega{dollar}3 PUFAs relative to suspended particles throughout the water column due to bioassimilation by zooplankton, which resulted in lower settling flux and higher vertical flux through animal pathways. The active transport pathway: bioassimilation, net vertical flux of biomass, and loss by predation directly into the POC pool, was estimated to account for {dollar}>{dollar}95% of the vertical flux of {dollar}omega{dollar}3 PUFAs and a significant fraction of the total POC flux out of the euphotic zone in an oligotrophic warm-core ring. These results indicate that a compound's biogeochemical behavior in the upper ocean is directly related to its biochemical reactivity and the extent of its involvement in biological cycles.