The flux of bio- and lithogenic material associated with sinking particles in the mesopelagic 'twilight zone' of the northwest and North Central Pacific Ocean

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Lamborg, CH, Buesseler, KO, Valdes, J, Bertrand, CH, Bidigare, R, Manganini, S, Pike, S, Steinberg, D, Trull, T, Wilson, S
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon 2008
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Pacific; Subarctic
• Online Access: http://www.sciencedirect.com; https://doi.org/10.1016/j.dsr2.2008.04.011; http://ecite.utas.edu.au/54598

As part of the VERTIGO program, we collected and analyzed sinking particles using tethered andneutrally buoyant sediment traps at three depths in the oceanic mesopelagic zone and at twobiogeochemically contrasting sites (N. Central Pacific at ALOHA; N. Pacific Western Subarctic Gyre atK2). This effort represented the first large-scale use of neutrally buoyant traps and represents asignificant step forward in the study of the marine biological pump. In this paper, we present the resultsof mass, macronutrient, biominerals and phytoplankton pigment determinations made on thesesamples.The impact of a variety of potential collection biases were examined, including those from in-trapparticle degradation, zooplankton swimmers and poisons. Though these factors have been observed toaffect results in other programs, we found them to have relatively little impact on measured fluxes inthis study. There was evidence, however, that the neutrally buoyant traps performed better than thetethered traps in terms of flux accuracy during one deployment, possibly because of improved largeparticle collection efficiency.Fluxes of material exhibited three different patterns through the mesopelagic: increasing, decreasingand constant with depth. Decreasing fluxes with depth were observed for all biogenic material formedin the euphotic zone. The attenuation of flux with depth was not the same for all components, however,with phytoplankton pigments exhibiting the greatest degradation with depth and particulate inorganiccarbon the least. Organic carbon and nitrogen showed a very high correlation in these samples, withlittle evidence of different attenuation length scales. Increasing fluxes with depth were observed forparticulate Ba at both sites and Al at K2. The increases in Ba are attributed to the formation of barite indegrading particles, while increasing Al at K2 was the result of lateral inputs from a continental shelf/slope. Constant fluxes with depth were observed for Al at ALOHA, where fluxes appeared to be in steadystate with atmospheric dust deposition.The mesopelagic zone at K2 was observed to attenuate particle flux less than at ALOHA, and with ahigher POC/PIC (rain) ratio. These two factors combine to imply that the Subarctic province had amuch more efficient biological pump than had the subtropical gyre during our occupations. This couldbe the result of either faster sinking particles, generated from grazing by large zooplankton, orinherently slower particle degradation rates.