Distribution and fluxes of aggregates >100 μm in the upper kilometer of the South-Eastern Pacific

Abstract

Large sinking particles transport organic and inorganic matter into the deeper layers of the oceans. Between 70 and 90% of the aggregates exported from the surface mixed layer are disaggregated within the upper 1000 m. This decrease with depth indicates that fragmentation and remineralization processes are intense during sedimentation. Generally, the estimates of vertical flux rely on sediment trap data but difficulties inherent in their design limit the reliability of this information. During the BIOSOPE study in the south-eastern Pacific, 76 vertical casts using the Underwater Video Profiler (UVP) and deployments of drifting sediment traps provided an opportunity to fit the UVP data to sediment trap flux measurements. We applied the calculated UVP flux in the upper 1000 m to the whole 8000 km BIOSOPE transect. Comparison between the large particulate material (LPM) abundance and the estimated fluxes from both UVP and sediment traps showed different patterns in different regions. On the western end of the BIOSOPE section the standing stock of particles in the surface layer was high but the export between 150 and 250 m was low. Below this layer the flux values increased. High values of about 30% of the calculated UVP maximum surface zone flux were observed below 900 m at the HNLC station. The South Pacific Gyre exported about 2 mg m^−2 d^−1. While off Chilean coast 95% of the surface mixed layer matter was disaggregated, remineralized or advected in the upper kilometer, 20% of the surface zone flux was observed below 900 m near the Chilean coast. These results suggest that the export to deep waters is spatially heterogeneous and related to the different biotic and abiotic factors.