RSBE² Seminar - MAry Eliot and Gildas Ratié
Mary Elliot and Gildas Ratié from LPG, Nantes
April 5 at 2pm, Salle Pondaven - ISOMer
Gildas Ratié: Metal cycle in contaminated wetlands under climatic and anthropogenic forcing: insights of coupling metal isotope systematics and synchrotron techniques
The biogeochemical cycles of metals have been profoundly disrupted by anthropogenic activities, particularly since the industrial revolution. These activities as well as the impacts linked to climate forcing are at the origin of significant flows and mobilization of metals, particularly towards soils and continental waters. Within the Earth critical zone, soils and sediments act like sinks, particularly in wetlands with significant metal trapping capacities, acting as accumulator filters through their hydrological cycle (high water/low water) controlling biogeochemical processes. Climate models predict that the frequency, intensity and number of heavy precipitation events will increase as the global climate evolves. This state of affairs no longer makes it possible to precisely constrain the fate and source-sink balance of metals in the environments and consequently of the overall contributions from the continent to the oceans. The joint use of isotopic tracers and the study of the speciation of elements by X-ray spectroscopy on synchrotron, makes it possible to identify and finely quantify the process at the origin of the flows of metals between the different natural reservoirs.
Bio: With an academical background in chemistry, I moved to environmental sciences for deciphering the pathways of the contaminants (mainly inorganics) at the Earth surface. I defended my PhD in 2015 at Université Paris Sud and I travelled from Brazil, Czech Republic and France before to settle down at Nantes where I got a permanent position as associate professor in 2023. I mainly use the tools of isotopic geochemistry and X-ray absorption spectrocospy to identify at a molecular scale the mechanism responsible for the contaminant speciation in the continuum water-soil-plant. My research study fields belong to old mining and smelting sites and wetlands under temperate and tropical climates.
Mary Elliot: The shells of marine bivalves are potential bio-indicators of current and past environments
The shells of marine bivalves are formed by successive layers of calcium carbonate which record the physicochemical conditions of the aquatic environment in which they were formed. The analysis of the geochemical composition of these successive layers of CaCO3 therefore makes it possible to obtain temporal profiles of the environment throughout the lifespan of the bivalve. Some species of bivalves live for decades or even hundreds of years. Bivalve shells therefore have the potential to be used as bio-monitors of current and past environments with seasonal interannual and decadal timescales. The aim of this seminar is to present the work that we are carrying out at LPG on several species of bivalves: 1- the species Glycymeris glycymeris (Amande de mer) which records the concentrations of lead in its environment and 2- the species Tridacna gigas (giant clams) which records climate variability in the Tropical Pacific zone.
BIO: I obtained a PhD in earth science in the field of paleoclimatology using microfossils (foraminifera) embedded in sediment deposits to reconstruct abrupt climate change in the North Atlantic Ocean. I obtained my PhD in 1999 at the Laboratoire des Sciences du Climat et de l'Environnement, in France. I did a first post doc at Lamont Doherty Earth Observatory, Columbia University (1999-2001) then a second post doc at the Research School of Earth Science in Canberra, Australia (2001-2002). I was a Lecturer for 10 years at the School of Geoscience in Edinburgh, Scotland before obtaining a Professorship at Nantes University in 2012.
My research focuses on understanding the relationships between changes in ocean circulation and past and present climate change. I use geochemical tracers such as stable isotope (del-18O and del-13C) and trace elements (Sr, Mg, Ba, Pb) measured on marine microfossils and bivalves. These proxies provide quantitative estimates of past changes in ocean salinity and temperature with seasonal resolutions. One active area of research focuses on reconstructions of past El Niño Southern Oscillation (ENSO) patterns using marine bivalves. Marine bivalves have the advantage of providing paleoenvironmental records with seasonal resolutions at high and low latitudes. My research focuses on modern and fossil giant long-lived Tridacna specimen in order to assess their potential to reconstruct present and past changes in ENSO. Another area of research aims to reconstruct metal concentrations in the environment, such as Pb in shells of Glycymeris glycymeris.