Abstract:
This research attempts to determine the role - CO2 source or sink - of the
Southern Ocean on a regional and seasonal scale by implementing an
integrated multidisciplinary approach which combines in situ
measurements, studies of process in laboratory controlled conditions
and numerical computation. It approaches the whole of the processes
which govern the cycle of carbon in the Southern Ocean, from
... exchanges
of CO2 at the air/sea interface until to accumulation of carbon in the
sediments. It is based on a mechanistic scientific approach which aims
at improving comprehension of the production process and of
mineralisation of carbonated biomass in surface water as well as
export towards the deep ocean. In particular, the roles of light and the
availability in nutrients (major and minor) in the determination of the
dominant phytoplanktonic community, and thus of the dynamics of the
associated food chain and the carbon exportation, will be studied in
areas dominated by various phytoplanktonic communities, namely the
diatoms, the colonies of Phaeocystis and the nanophytoplankton. The
role of aggregates as carbon conveyors, from surface to the deep water
and the sediments, will be investigated with special attention to the
following processes : the bacterial mineralisation of aggregates and
the production and fate of the barite proxy.
The use of the barite as tracer of the exported carbon flux will be evaluated
in order to improve the existing transfer functions. Acquired knowledge will
then be integrated in a 1D physical and biogeochemical model able to
simulate the cycle of carbon as well associated biogenic elements (N, Si,
Fe, Mn, Ba) in the whole water column of the Southern Ocean over a
seasonal cycle. All together, this study will contribute to establish a
diagnostic and predictive model which will be used to evaluate the role
of the Southern Ocean in a global perspective. 
