MSC.Geol. Andreas Basse

„Alteration of particulate organic matter during vertical sinking and lateral transport“. – A study on biomarkers in the water column of the NW-African upwelling system

Particulate organic matter (POM) plays an important role in the global carbon cycle, since its production in the surface waters and subsequent export to the deep ocean and sediments causes a net removal of CO2 from the atmosphere. Previous studies have shown the efficiency of particle transport between the surface and the deep ocean is largely influenced by the composition and physical characteristics of larger organic-rich particles such as marine snow. Field observations and models show that these particles are not only transported vertically, but also by lateral advection in intermediate and near-bottom nepheloid layers (NLs). However, little is known about the biomarker composition of these sinking particles and how it is altered during sinking and lateral transport.

The study area, the NW-African upwelling system, is characterized by high primary production and export of POM. The continuous occurrence of NLs and an exceptional particle flux record from this area (spanning from 1988 until now) make the region an ideal place for my study.

The aims of the project are to:

- study the alteration of the biomarker composition of particles during sinking and following re-suspension from near-shore areas
- identify the role of microbial degradation and alteration of the organic matter
- assess the contribution of lateral transport in nepheloid layers to the total particle flux
- reveal the origin of laterally transported material
- quantify the contribution of pre-aged material to total particle fluxes and to fluxes of individual biomarkers


Sample material from the water column and from surface sediments collected during several cruises, and from sediment traps is analyzed. Abundance measurements of organic compounds are coupled with compound-specific stable isotope analysis in order to monitor and quantify selective degradation and possible effects on the isotopic composition of organic biomarkers. Biomarker data are compared with information on microbial diversity on the sinking particles, which is provided from collaboration partners at MPI Bremen. Radiocarbon measurements distinguish between freshly produced organic carbon and resuspended older material. Another focus will be the use of compound-specific radiocarbon dating of selected biomarkers to explain the transport and alteration processes of particulate organic mater in the water column.