Logo Universitat Bremen
Page path:

RV POSEIDON P 425

During the cruise to the coastal upwelling area off Cape Banc (Mauritania) we conducted particle flux studies using moored sediment traps, free-drifting sediment traps (see pictures to the upper right), in situ pumps, water samplers and the multiple plankton net for the collection of zooplankton. We were lucky as we came into a dust storm at the beginning of the station work on January 18/19., 2012 (lower right). For the first time, this provided as a chance to study the potential effect of dust on the biological pump. Shortly after the onset of this event, we deployed two free-drifting sediment traps.

Abstract (proposal by Fischer, Iversen and Mollenhauer)
The coastal upwelling area off NW Africa is a highly dynamic production system where organic material is transported offshore via filaments and eddies. This transport and the decay of organic carbon in the water column are dependent on the sinking velocities of larger ‘marine snow’ particles and zooplankton fecal pellets, which in turn are controlled by various ballast minerals. During the cruise, we plan to perform maintenance and exchange of instrumentation at the two mooring systems CB and CBi off Cape Blanc (Mauritania), which are equipped with sediment traps, oceanographic instruments, and optical systems attached to a technical platform (MSD=Multi-Sensor-Device). The MSD-platform with a video system has been deployed the past two years and provided novel data on bi-daily particle concentrations and size-distributions at 1200 m depths at site CBi where trap fluxes are recorded with approximately weekly resolution. Long-term records of particle fluxes have already been obtained since 1988 at the mesotrophic site CB and since 2003 at the eutrophic site CBi, serving to document potential changes in the ecosystem of the NW African coastal upwelling. Additionally, short-term flux changes, the composition and decay of larger particles will be studied using free-drifting sediment traps deployed at the eutrophic station CBi. We plan to obtain high vertical and horizontal resolution of particle distributions at 11 stations with vertical imaging profiles using a 16 MPixel camera and turbidity sensor. At selected key stations, the composition of organic material, in particular the concentrations of individual biomarkers in relation to water depth and particle sinking velocities as well as the bacterial populations on sinking particles shall be investigated. Direct measurements of aggregate size-specific degradation, sinking velocities, microbial degradation, bacterial community, and chemical composition will be performed on aggregates re-formed from in situ collected water samples in roller tanks and related to the in situ measurements. By combining in situ particle observations, experimental microbiological studies, and organic-geochemical analysis in a high resolution transport model (with aggregation and NPZD-ecosystem modules), we expect to gain a better understanding of particle transport, aggregation and disaggregation as well as remineralization processes in the water column on longer time scales.
Contact:

Dr. Gerhard Fischer

Phone: 

+49 421 218-65080

Fax:

+49 421 218-65099

Email:

Room: 

GEO II, Raum 1430