Changes in the occurrence of heavy metals in polar ice during the last climatic cycles, with special emphasis on the possible link between cosmic dust accretion rate and the 100 kyr cycle

During the last decades, ice cores drilled in Antarctica and in Greenland have provided time series of data that have allowed the characterisation of variations of natural and anthropogenic heavy metals in the past atmosphere. Nevertheless, the interactions of heavy metals with climate change and their transport patterns remain largely unknown during the last climatic cycles. Hereafter we present our project dealing with the assessment of past changes of various heavy metals in Antarctic and Greenland ice during the past = 500 kyr anticipating some preliminary Zn measurements in the EPICA Dome C ice core back to about 200000 years. In our project special emphasis is given to Pt group elements (PGE) that are tracers of interplanetary dust particles (IDPs). Tracers of crustal material, volcanic activity and ocean paleoproductivity are also investigated. At the moment we are focusing especially on the ongoing EPICA Dome C Antarctic ice core, decontaminating mechanically some section and perfonning preliminary measurements of Zn and Al using Graphite Fumace Atomic Absorption Spectrometry and adopting ultraclean procedures. These data confinn the prominent continental origin of Zn in the East Antarctic ice during the last and penultimate glacial period.

One hundred fifty-year record of lead isotopes in Antarctic snow from Coats Land

A record of the concentrations of Pb and Ba and the isotopic composition of Pb has been established for a remote, low accumulation site in the Atlantic sector of Antarctica (Coats Land) by means of thermal ionization mass spectrometry. The snow samples cover the period similar to 1840 to 1990. They were taken from the walls of a pit to a depth of 7.8 nu and as a core to 16 m; ultraclean procedures were used. Detailed laboratory subsampling provided both long-term (secular scale) and short-term (intra-annual) Pb, Ba, and Pb isotope variations. The results show that there have been significant variations in Ph concentrations (range, 0.1 to 9.3 pg/g) and isotopic composition (range, 1.096 to 1,208 for Pb-206/Pb-207 ratio) since the 1840s. The data show evidence of pollution for this metal in Antarctica as early as the 1880s. Several Pb maxima were observed: the first at the beginning of the 20th century and the last in the 1970s to 1980s, with a clear decrease during recent years. Although the last maximum is clearly linked to the rise and fall in the use of leaded gasoline in the Southern Hemisphere, especially in South America, the reason for the first remains uncertain. The pattern of changing isotopic composition of Ph reveals the changing origin and character of the anthropogenic inputs to Antarctica. An interesting feature in this pattern is the relatively large contribution of unradiogenic Pb in the similar to1890s, possibly originating from Australia. Another interesting feature is the pronounced intra-annual variation in the isotopic composition of Pb, which illustrates the complexity of the changing inputs of Pb to Antarctica

Trace elements in accreted ice from the Vostok sub-glaciallake, Antarctica: Initial results

We present in this study initial results on trace elements concentrations changes in the deepest part of the Vostok ice core. From 3310 m depth to the bottom of the ice core (3623 m), ice encountered is made of disturbed glacial ice by glacier dynamics and accreted ice from the sub-glacial lake Vostok. Since trace elements are involved in various biogeochemical processes, studying these elements in the accreted ice of the Vostok lake can lead to a better understanding of lake chemistry and life development in such extreme environment. Because concentrations to be measured in Antarctic ice are exceedingly low, such investigations on trace éléments require strict control of contamination problems and the use of ultraclean protocols. Initial results obtained for Zn concentrations changes show high variability ($<$0.5 to 32 pg/g), with the lowest concentrations found in the accreted ice of the Vostok lake ($<$00.5 pg/g). According to crustal enrichment factors close to unity, Zn seems to be mainly associated with crustal material

Meteoric smoke fallout over the Holocene revealed by iridium and platinum in Greenland ice

An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65million years ago1. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate2 or the nano- phase material of the vaporized impactor3. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000 years ago, from a Greenland ice core4. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre- sized meteoric smoke particles5,6, formed from the recondensa- tion of ablated meteoroids in the atmosphere at altitudes >70kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation7 and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 6 5 kilotons per year of meteoric smoke during the Holocene

Trace elements in Vostok Antarctic ice during the last four climatic cycles

International audienceLi, V, Cr, Mn, Co, As, Rb, Sr, Ba, Bi and U were determined by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in various sections of the 3623 m Vostok deep Antarctic ice core dated from 4600 to 410,000 years BP, which corresponds to the last four climatic cycles back to isotopic stage 11.3. Concentrations of all elements were found to be highly variable with low values during interglacial periods and warm interstadials and much higher values during the coldest periods of the last four ice ages. Crustal enrichment factors suggest various sources for the different elements. Rock and soil dust is the dominant source of V, Mn, Rb, Ba and U whatever the period, and of Li, Cr, Co, Sr and As during cold periods. Sea salt aerosol, together with aeolian dust, also contributes significantly to Sr whereas volcanic emissions could provide a significant input for As and Bi especially during warm periods

Direct determination of mercury at the sub-picogram per gram level in polar snow and ice by ICP-SFMS

An analytical method for the direct determination of mercury (Hg) in polar snow and ice cores and surface snow based on inductively coupled plasma sector field mass spectrometry (ICP-SFMS) has been developed. Various Hg isotopes, such as Hg-199, Hg-200, Hg-201 and Hg-202, appear to be free of polyatomic interferences in such matrices and allow the measurements to be made in low resolution mode, leading to high sensitivity. Ultra-low concentration Hg standards (from 1.5 to 20 pg g(-1)) were used for the calibration of the Thermo Finnigan MAT Element2, and a detection limit as low as 0.18 pg g(-1) was achieved using Hg-202. Ultra-clean procedures used from field sampling to final laboratory analysis show no significant blank contributions and appear suitable for the reliable determination of Hg at ultra-low concentrations. Precision of the Hg measurements was estimated to be 15% in terms of relative standard deviation on five replicates and accuracy was checked with an analytical reference material (102% recovery). Hg concentrations in surface snow samples from the Northern Hemisphere collected in the Canadian Arctic and in Svalbard (Norway) show high variability (1.2-32.0 pg g-(1)). In Antarctica, Hg was determined in different ice core sections from Dome C, spanning the last 18000 years BP (range from 0.7 to 3.2 pg g(-1)), and in snow samples from Coats Land covering the last 150 years (range from 0.2 to 16.1 pg g(-1))

Meteoric smoke fallout over the Holocene revealed by iridium and platinum in Greenland ice

An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65million years ago1. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate2 or the nano- phase material of the vaporized impactor3. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000 years ago, from a Greenland ice core4. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre- sized meteoric smoke particles5,6, formed from the recondensa- tion of ablated meteoroids in the atmosphere at altitudes >70kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation7 and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 6 5 kilotons per year of meteoric smoke during the Holocene