ALBERT

Description: A one-dimensional model "ADAM" is presented that allows the prognostic computation of the interactions between mineral particles (dust) and biologically formed aggregates. The model couples a 7-compartment biogeochemical component (NO(3), NH(4), phytoplankton aggregates, zooplankton, detritus, carbon, and chlorophyll) and a 4-compartment component for the tracing of mineral particles: single free particles in the water, particles aggregated with phytoplankton, incorporated in zooplankton, and attached to detritus. It resolves both annual and daily cycles of plankton and the fate of dust from eolian import into the ocean via biological activity, aggregation and disaggregation to sedimentation at the sea floor. The model results suggest that particle scavenging is essentially occurring in the mixed layer, where biological activity and shear aggregation regulate the formation of the aggregates. The aggregates interact intensively with the suspended pool of dust particles, and sink through the upper main thermocline with increasing speed. Particle break up and organic matter degradation are important mechanisms for particle cycling in the intermediate and deeper layers. The model predicts an 80% decrease of the annual carbon flux between 100 m and 3000 m depth. The vertical profile of Al-contents in suspended particulates and the annual average vertical flux of particulate organic matter are fairly well reproduced by the model, as well as the seasonal cycles of carbon and dust fluxes in the ocean interior. (C) 2010 Elsevier B.V. All rights reserved.

Description: Circumpolar surface waters dominate the circulation of the Southern Ocean and sustain one of the ocean's largest standing stocks of biomass thereby producing a significant output of biogenic components, mainly diatoms, to the bottom sediments. Generally transit of biogenic matter from the sea surface to the sea floor affects nutrient regeneration fuels benthic life and transfers signals to the sediment record1–5. Reliable quantification of the relationship between biological production, fractionation of skeletal and tissue components and bottom sediment accumulation depends on direct vertical flux measurements from sediment trap deployments6–9, which have proved to be most scientifically productive10–13. We now present data on vertical mass fluxes from the Southern Ocean and evidence for strong biogeochemical fractionation between organic carbon-, nitrogen- and phosphorus-containing compounds, siliceous and calcareous skeletal remains, and refractory aluminosilicates.