Accueil > Actualités > Séminaires > Séminaire de Gesine MOLLENHAUER (LSCE)


Titre : Tracing transport processes in the ocean - evidence from compound-specific radiocarbon and particle-class specific radionuclide data
Nom du conférencier : Gesine Mollenhauer
Son affiliation : AWI Bremerhaven and MARUM, Allemagne
Laboratoire organisateur : LSCE
Date et heure : 24-06-2010 11h00
Lieu : LSCE Vallée, Bat 12, Campus CNRS de Gif-sur-Yvette
Résumé :

Organic matter deposited in marine sediments is a large reservoir of carbon and represents an important sink of carbon on millennial time-scales. Furthermore, organic matter including source-specific biomarkers deposited in marine sediments provides a valuable archive for the reconstruction of past environmental conditions. However, the depositional history of the organic sediment fraction needs to be well-understood in order to correctly interpret those records.

Compound-specific radiocarbon dating of source-specific biomarkers is a tool to determine timescales of transport affecting organic matter prior to its deposition in marine sediments. Using terrigenous biomarkers in marine sediments, information on mean residence time on land can be obtained. Fluvial and aeolian transport supply terrestrial organic matter of different age likely derived from different sources. I will discuss examples from climatically distinct regions in order to elucidate the rate of carbon turnover under different climates.

Redistribution of sediments within the oceans is a further important process affecting marine sediments which has the potential of resulting in the deposition of pre-aged material. Deposition of re-suspended marine organic matter can be detected and characterized by compound-specific radiocarbon dating of marine biomarkers. However, the quantification of laterally supplied material remains difficult, in particular since hydrodynamic sorting of particles during transport will likely affect sediment grain-size and particle-type composition. Radioisotope proxies for lateral sediment supply are commonly based on bulk measurements and assume uniform radionuclide inventories across sediment constituents. I will present combined compound-specific radiocarbon data of marine haptophyte biomarkers and radionuclide evidence for sediment transport. Results from grain-size specific 230Th-excess measurements imply that sorting of particles during transport needs to be considered in order to accurately characterize sediment redistribution.