Thorium-234 based estimation of residence time of bottom-near particulate matter in the Mecklenburger Bucht .

• Applicant: Professor Dr. Gerhard Graf
• Subject Area: Oceanography
• Term: from 2012 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 233255247

Particle fluxes between water and sediments represent a significant fraction of the matter cycling between the pelagic and benthic system. Thus a permanent exchange between the benthic turbidity zone (BTZ) and the bioturbated sediment layers is provided, which in the case of the deep-sea occurs in the time scale of a few days (resuspension loop).This proposal aims to determine residence time of particles in the water, the BTZ and the sediment of the south-western Mecklenburger Bucht using the 234 Thorium/238Uranium equilibrium. In order to apply this approach, which was proven for the deep-sea, in a shallow water situation, some specific constraints have to be considered, especially the adsorption of Thorium on particles with higher mineral content and with relatively fresh organic compounds (Alginin, Fucoidan und Chondroitin; Co-operation with Prof. Carol Arnosti, Chapal Hill, USA). In addition flume experiments should be carried out in order to test the effect of increased turbulences and bottom shere on the thorium adsorption. The second year is dedicated to a field study to measure residence time and POC on a transect from shallow sandy to deeper silty sediment. Thus the residence time of POC in different types of sediments and the other compartments of the resuspension loop can be calculated.

• DFG Programme: Research Grants