Particulate carbon and nitrogen fluxes and compositions in the central equatorial Pacific

Mass, carbon, and nitrogen fluxes and carbon and nitrogen compositions were determined for particulate samples from plankton net tows, shallow floatin g sediment traps, intermediate and deep moored sediment traps, and sediment cores collected along 140 degreesW in the central equatorial Pacific Ocean during the US JGOFS EqPac program. Mass, particulate organic carbon (POC), and particulate inorganic carbon (PIC) fluxes measured by the floating sed iment traps during the Survey I (EI Nino) and Survey II (non-El Nino) cruis es follow essentially the same pattern as primary production: high near the equator and decreasing poleward. POC fluxes caught in free-floating traps were compared with alternative estimates of export fluxes, including Th-234 models, new production, and other sediment trap studies, resulting in wide ly differing estimates. Applying Th-234 corrections to the trap-based fluxe s yielded more consistent results relative to primary production and new pr oduction. Despite factors of five differences in measured fluxes between di fferent trap types, POC:Th-234 ratios of trap material were generally withi n a factor of two and provided a robust means of converting modeled Th-234 export fluxes to POC export fluxes. All measured fluxes decrease with depth . Trap compositional data suggest that mineral "ballasting" may be a prereq uisite for POC settling. POC remineralization is most pronounced in the epi pelagic zone and at the sediment-water interface, with two orders of magnit ude loss at each level. Despite seawater supersaturation with respect to ca lcium carbonate in the upper ocean, 80% of PIC is dissolved in the epipelag ic zone. Given the time-scale differences of processes throughout the water column, the contrasting environments, and the fact that only 0.01% of prim ary production is buried, sedimentary organic carbon accumulation rates alo ng the transect are remarkably well correlated to primary production in the overlying surface waters. POC to particulate total nitrogen (PTN) ratios f or all samples are close to Redfield values, indicating that POC and PTN ar e non-selectively remineralized. This constancy is somewhat surprising give n conventional wisdom and previous equatorial Pacific results suggesting th at particulate nitrogen is lost preferentially to organic carbon. (C) 2001 Elsevier Science Ltd. All rights reserved.