Agenda

Dr. Lara Pozzato, University of Aix-Marseille

Abstract:
Marine sediments have long been recognized as both source and sink of carbon, depending on the environmental conditions and on the geographic area taken into consideration. Organic Matter can be buried and stored in sediments or be remineralized and transformed in biomass and CO2 and return to the water column and, finally to the atmosphere. Many factors contribute to determine this fragile equilibrium in the carbon cycle and climate change, because of its multiple consequences on marine ecosystems, can alter these processes and destroy the natural balance. In particular, the temperature rise in the atmosphere and in the oceans induces more and more the formation of hypoxic and anoxic zones, both at large and on the coast. The temperature rise in fact, enhances the degradation of phytoplanktonic blooms and induces stratification, causing a positive feedback in maintaining hypoxic conditions, promoting the release of high quantity of nutrients from the sediment to the water column and causing the accumulation of organic matter in the superficial sediments, which creates the so called “sedimentary debt”. Also ocean acidification, another consequence of climate change and anthropization, can have a great impact on the fate of carbon in marine sediments. The lowering of the pH in oceans and seas modifies the balance between the different forms of DIC with an increase of CO2 and bicarbonate ions (HCO3) and a decrease of carbonate ions (CO3). Coastal areas are a natural storage of CO2 and therefore play a very important role in the global carbon cycle. Because of the shallow depth, in coastal areas the chemistry on the water column is also tightly linked to the biogeochemistry of the sediments and thus to the DIC, total alkalinity (TA) and calcium fluxes. It is therefore logic that acidification impacts firstly and more severely the coastal zones, in particular in polar and sub-polar regions where colder ocean waters can dissolve higher concentrations of CO2 comi ng from all over the planet thanks to winds and the general atmospheric circulation.

Bio Sketch:
Lara Pozzato graduated in Environmental Marine Sciences at Trieste University, and continued her education in the Netherlands, where she completed a PhD position in biogeochemistry and carbon cycle at the Department of Ecosystem Studies of the NIOO/NIOZ and University of Utrecht under the supervision of Prof. Jack Middelburg and Prof. Karline Soetaert. She therefore moved to France, at CNRS in Gif sur Yvette, working with dr. Christophe Rabouille, and finally at the University of Aix-Marseille, working with Dr. Christian Grenz and Prof. Olivier Radakovitch (CEREGE). She specialized in biogeochemistry of deep sea and coastal marine sediments with particular focus on ecosystem studies, the impact of hypoxia-anoxia and ocean acidification on the early diagenesis processes and on the structure and functioning of benthic community. She studied the carbon cycle and remineralization by analyzing biomass and biodiversity of the benthic community, using tracers, stable isotopes and radiocarbo n, oxygen microprofiles and controlled sediment core incubations.