Characterization of marine CaCO3 particles in the context of Global Change

The expected increase in greenhouse gasses concentrations as a result of human activity is
leading to significant climate change in the coming years. The fate of the anthropogenic CO2 has
been intensively studied. Being the largest reservoir of reactive carbon, the ocean acts as an
important sink for anthropogenic CO2 and plays a significant role on the global biogeochemical
cycle of carbon and its perturbations. There remain, however, large uncertainties concerning the
uptake of carbon by the ocean, mainly due to insufficient knowledge of processes controlling the
carbonate chemistry in surface waters. The effects of precipitation of calcium carbonate by
calcifying organisms in the euphotic zone and redissolution of their skeletons have not been fully
taken into account. This precipitation-dissolution process affects both the concentration of
dissolved inorganic carbon and of total alkalinity and plays thus a significant role in the
buffering capacity of seawater and its potential to act as a sink or a source of CO2 for the
atmosphere. We aim to study the processes associated with the oceanic production and
dissolution of CaCO3 in order to quantify the role of calcifying phytoplanktonic organisms in
sequestering CO2. The calcareous skeletons of Coccolithophores, which comprise one of the
main groups of calcifying organisms in the photic zone of the ocean, are analysed.
The gut content of copepods, which grazes on coccolithophores is examined by different
methods like Electron Probe Micro-Analysis (EPMA) and Micro X-Ray Fluorescence (M-XRF)
in order to detect the possible dissolution features at the calcite surface. Automatic EPMA is
used for the characterization of individual particles from ocean samples for their composition,
morphology and size. Subsequent statistical processing techniques classifies the particles into
specific particle clusters.