Evolution naturelle des éléments présents à l'état de traces (métaux lourds, métalloides, terres rares (REE) et isotopes du plomb) dans la carotte de glace EPICA/Dome C (Antarctique de l'Est) de 263,000 à 671,000 ans avant nos jours

摘要

The study of climate necessarily involves the collection and processing of large amounts of data gathered from polar ice cores which are an excellent way of finding how the climate has changed. In this context, I provide the longest records of crustal elements, metals, metalloids, rare earth elements, lead isotopes and mercury taking advantage of the 3270m EPICA/Dome C ice core located in East Antarctica. These elements have been studied in various sections of the EPICA/Dome C deep ice core from 263 ky to 671 ky BP. For crustal elements, metals, metalloids, rare earth elements and mercury, the analyses were performed by Inductively Coupled Plasma Sector Field Mass Spectrometry whilst the analyses of lead isotopes were performed by Thermal Ionization Mass Spectrometry and the analyses of mercury species (methylmercury and inorganic mercury) by Inductively Coupled Plasma Time of Flight Sector Field Mass Spectrometry, in clean room conditions.The study of crustal trace elements (V, Cr, Mn, Fe, Co, Rb, Ba and U) allowed to document large natural variations in the occurrence of several crust derived elements in Antarctic ice from 263 to 671 ky BP. I show that the concentrations were highly variable, with low values during warm periods (interglacials) and much higher values during the coldest stages (glacial maxima). The advection of crustal trace elements to the East Antarctic plateau is found to occur when a well-defined critical δD value (~ - 430‰) was reached. For the first time, the rare earth elements (REE) were analyzed in a deep ice core. The REE of continental origin windblown to the East Antarctica have been studied for their geographical provenance during this time period. In this way, crustal trace elements provenance in glacial and interglacials epochs has been identified through the rare earth elements signature and sediments from Potential Source Areas (PSA) of the Southern Hemisphere. During less pronounced glacial maxima (MIS 12.2, 12.4 and 14.2) at Dome C in East Antarctica, REE show that dust materials come from at 50% to Australia and at 50% to Córdoba province whilst during more pronounced glacial maxima (MIS 8.2, MIS 10.2, 10.4 and 16.2) they come from at 90 to 80% to Córdoba province and at 10 to 20% to Australia. Moreover, Antarctic dust during interglacial periods consist of a mixture of South America (South Argentina, Central Argentina and perhaps Patagonia), the Transantarctic Mountains (Koettkitz glacier) and Australian materials.Metals and Metalloids concentrations have been performed from 263 to 671 ky BP in order to examine the long-term variability, from which important information about the contribution of various sources and the transport patterns can be inferred. The concentrations were highly variable with low values during warm periods and high values during cold periods. However, the maximum amplitude of the variations markedly differs from one element to another. In particular, lead isotopes data provide an important contribution to the developing understanding of the variation of continental dust compositions present across Antarctica.Finally, for the first time, total mercury, methylmercury and inorganic mercury have been measured in a deep ice core. It can be observed that concentration values varied considerably, with low values during interglacials and higher values during the coldest periods. The determination aimed at determining possible variations in oceanic paleoproductivity and Hg deposition processed over 671 ky BP.