Marie Duflos (PhD student)

The organic matter (OM) is one of the most active geochemical tanks which interests, on a large scale, the carbon cycle. Of complex structure, the OM has a behaviour, a stability and a fate highly variable according to environmental conditions. OM bioavailability determines the labile, semi-labile and/or refractory character of OM that in fine controls remineralisation to CO2 versus preservation. It is thus our objective to better define the origin of the totality of this OM, as well as the various stages and the various mechanisms involved in its transformation.

In the water column, and as by product of primary production, dissolved organic carbon is released in seawater from particulate material and is subsequently taken up by free-living bacteria which in turn produce CO2 through respiration in proportion difficult to determine on a global scale. Such processes are relevant to carbon cycle since they determine which part of organic and inorganic carbon is sequestered in the Ocean interior. Recent studies indicated that bacterial degradation of organic material might be better described with a better knowledge of the chemical composition of organic material as well as with an appropriate estimate of some bacterial parameters such as bacterial growth efficiency and organic material turnover rate.

In sediments, bioturbation by benthic infauna continuously introduces temporal and spatial heterogeneity through processes such as feeding, burrowing and bioirrigation activities. Activities of benthic organisms influence the transport of particles and solutes in surface sediments in a variety of direct and indirect ways, drastically altering organic matter mineralization pathways, sediment reaction rates, and general ecosystem properties from what would occur in their absence.