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Climatic tales from EPICA/Dome C ice core
Since few decades, it has become obvious that the two large ice sheets in Antarctica and Greenland contain paleoclimatic information. There is a bidding war going on in Antarctica. This bidding started with 80,000 for the Byrd ice core. Vostok raised the bid to 160,000 and then 420,000. Now a new ice core, the European Project for Ice Coring in Antarctica (EPICA) Dome C core, has raised a record of the longest time period possible, ~ 800,000 years ago, which corresponds to the Marine Isotopic Stage (MIS) 20.2 (Jouzel et al., 2007).
The ice contains information related to a host of environmental factors: temperature, wind speed and transport paths, sea ice extent, volcanism, oxidation capacity of the atmosphere, greenhouse gas concentration, marine biological activity, etc.
Most water is H216O, but the main reservoir (the oceans) contains a small proportion of HD16O and H218O. In nature, fractionation occurs during transfer between the condensed and vapour phases. In successive cycles of evaporation and condensation, the heavy molecules evaporate less easily and condense more easily. This reduces the amount of heavy isotopes (18O and D are depleted), so that δ values of precipitation are always negative. As an air mass containing water vapour from the oceans moves towards the poles, it is cooled and loses water vapour (condensation leading to precipitation). It therefore becomes more and more depleted in the heavy isotopes (δ becomes more negative).
Dansgaard et al. (1969) concluded that the most important factor governing δ values in precipitation is the temperature difference between the ocean source and the sampling site. Since sea surface temperatures are relatively stable compared to air temperatures at high latitudes, δ is most dependent on T at the time and place of deposition. Increasing δ’s upward in the core indicate warming climate, and decreasing δ’s indicate cooling climate in the course of time.
The deep-sea benthic oxygen-18 record (Lisiecki and Raymo, 2005) and the δDice Dome C record are in excellent overall agreement back to ~ 800,000 years BP (Figure 1.4.1). Such an agreement justifies the use of the marine sediment nomenclature for Marine Isotopic Stages (MIS).
From new experiments performed with an atmospheric General Circulation Model including water isotopes (Jouzel et al., 2007), it derives that Antarctic surface temperatures were up to ~ 4.5°C warmer compared to the late Holocene during MIS 5.5 and 9.3, and down to ~ 10°C colder for the coldest period (MIS 2). A strong and persistent obliquity component is identified in this record, and Jouzel et al. (2007) suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods.
Anthropogenic emissions of trace elements into the atmosphere
Many studies have been devoted to the estimation of anthropogenic fluxes of trace elements into the atmosphere, at global scale (Nriagu and Pacyna, 1988; Nriagu, 1990a,b,c; Pacyna and Pacyna, 2001, Wilson et al., 2006) or at regional scale (Pacyna et al., 1984; Pacyna et al., 2007). All these studies confirm that emissions stemming from human activities largely exceed natural fluxes at global scale for numerous trace elements.
Table 2.4.1 introduce estimation of anthropogenic fluxes for trace elements into the atmosphere for the year 1983 and 1995 (Nriagu and Pacyna, 1988; Pacyna and Pacyna, 2001). We can notice that, for most trace elements, anthropogenic flux estimates largely exceed natural fluxes. The only exceptions are Cr and Mn in which case natural sources are still dominant in global scale (Table 2.4.1). During the 20th century, demand for Pb and other metals has continued to increase, with ~ 90% of total mine outputs being during the 20th century (Nriagu, 1996). The discovery of alkyklead additives for gasoline in the 1920’s and their subsequent introduction worldwide has caused another increase in demand for Pb in the 20th century, and has also significantly increased the quantity of Pb emitted to the atmosphere (Bollhöfer and Rosman, 2000). Despite the withdrawal of alkyklead additives for gasoline, Pb still appeared significantly disturbed by anthropogenic activities in 1997 (Kakareka et al., 2004). The increase of oil consumption and its by-product significantly increased the quantity of V emitted to the atmosphere in the last decades (Planchon, 2002). As a result of the stringent regulations governing the emissions of toxic substances, such as carbon monoxide, from transport vehicles, many countries adopted catalytic converters in order to convert these harmful compounds into less harmful compounds. However, Pt, Pd and Rh, so-called Platinum Group Elements (PGE) are usually deposited on the surface of the monolithic ceramic support which is placed at the end of the exhaust stream system (Jacoby, 1999). In spite of the clear benefits obtained with the use of catalytic converters, the ever increasing use of theses devices might lead to PGE becoming widely dispersed in the environment. Many environmental matrices such as soil, road-side dust, atmospheric particulates etc. have been found to be enriched in PGE with respect to their background values (Barbante and Cescon, 2000).
For the other trace elements, estimates given between 1983 and 1995 indicate a decreasing trend of the anthropogenic emissions. This decrease could be due to the recent use of reduction system for particulate dust emissions or the treatment of gaseous effluents (Planchon, 2001).
Atmospheric transport of aerosols
Trace elements are transported through the air as particulates, and as such transport is dependent upon the size, shape, mass and other physical and chemical properties of the particles.
During long-range transport, the decrease in particle concentration (from the source a to the sink b) can be described as: Cb = Ca × f × e – t/ T.
Where t is the transit time between the source a to the sink b, T is the residence time in the atmosphere, governed by wet and dry deposition processes en route, Ca and Cb the atmospheric concentration at the source and the sink respectively, and f a correction factor. Therefore, the longer will be the transport time, the lower will be the concentration of trace elements at the sink. Particles can be removed from the atmosphere by dry or wet deposition. Dry deposition includes gravitational settling, where the settling velocity depends on the square of particle size, and turbulent mixing to the surface, while precipitation-related events like sub-cloud scavenging and in-cloud removal determine the wet deposition.
The removal efficiency is size dependent; hence during transport the size distribution changes. For sands and coarse silts the gravitational settling16 alone (dry deposition) determines the sedimentation velocity, while for clays the lifetime in the atmosphere is mainly controlled by wet deposition and turbulent mixing.
A parameterization of uplift and deposition (using analyzed winds and rainfall statistics) has been performed by Tegen and Fung (1994) and Tegen and Lacis (1996). The authors obtained atmospheric lifetimes spanning a very large interval, from one hour to about ten days, in function of particle size (Table 2.5.1 and Figure 2.5.1).
The first reliable evaluation of trace elements concentration in polar snow and ice
During the last five decades, considerable effort has been devoted by various laboratories to decipher the unique atmospheric archives stored in the successive dated snow and ice layers deposited from several hundred thousand years ago to present in the large Antarctic and Greenland ice caps. The earliest measurements of polar ice and snow were invalidated by contamination of the samples, but as it was recognized at the time, these studies concluded that urban areas was as unpolluted as the Earth’s most distant and isolated region: the polar ice sheets. In the 1960s, it was demonstrated that reliable results could only be obtained by strict observation and control of sample contamination.
Interest to measure heavy metals was stimulated in the early 1920s by Thomas Midgely (Nriagu, 1990) who discovered the extensive use of the lead additives for gasoline. Unfortunately, the challenge of demonstrating the threat to environment and health posed by widespread Pb emissions required the distinction of natural Pb levels from typical anthropogenic Pb levels, which was not recognized in the early 1920s. The invention of the atomic absorption spectrometer (AAS) in 1954 by Alan Walsh permitted easily the determination of Pb and other trace elements in various matrices. However, since no one was conscious of contamination issues at the time, the samples collected were entirely contaminated by anthropogenic lead.
The importance of contamination control was first realised in the 1960s by Clair C. Patterson and co-workers at the Department of Earth and Planetary Sciences of the California Institute of Technology (Caltech) (Flegal, 1998). When he became interested in snow and ice, Clair C.Patterson was already a famous scientist and had already given the first accurate determination of the age of the Earth (Patterson, 1956; Patterson et al., 1955). He pioneered the concept of contamination control in handling environmental samples (Patterson and Settle, 1976). However, Patterson’s efforts were distinguished not only in regard to the foresight and dedication shown to tackling the many challenges of trace-metal analysis, but also in the effort required to convince an establishment of scientists, governments and corporations that global heavy metal pollution was a real and imminent threat to society and the environment.
While Patterson and co-workers had earlier demonstrated the majority of Pb in urban air and coastal and open ocean waters to be due to the anthropogenic sources, they were yet to establish how Pb levels had changed over time. To do this, they measured trace elements, including lead, in snow and ice deposited in the Greenland and Antarctic ice caps. Extreme conditions were taken to minimize sample contamination (Murozumi et al., 1969). Murozumi et al. (1969) determined that lead concentrations in Greenland had increased significantly since 800 BC and linked these increases with important changes in the industrial and societal uses of Pb. They documented a very spectacular increase of lead concentrations in Greenland snow from the Industrial Revolution onward, up to concentration of ~ 200 ppt in the mid 1960s. A large part of this tremendous increase was observed after the 1930s and was clearly linked with ever-increasing use of lead additives in gasoline. This famous paper played a major role in the phasing out of lead additives.
In 1981, the reliable measurement of Pb in ancient Greenland and Antarctic ice was published, again by Patterson and co-workers (Ng and Patterson, 1981). It was the first time that someone was able to analyse accurately lead and other trace elements in deep ice cores whose outside had been highly contaminated during drilling operations. This was achieved by developing sophisticated procedures which allowed the decontamination of the contaminated core sections by chiselling successive veneer layers of ice in progression from the outside to the center, without transferring contamination present on the outside to the inner core. This major step will allow to obtain the accurate evaluations of concentrations of heavy metals in the 1990s in deep ice cores.
Studies of trace elements in Greenland and Antarctica
Other studies attempted to duplicate the results of Murozumi et al. (1969) from samples of snow and ice obtained from Greenland and Antarctica (Francis Hanappe and Edouard Picciotto at the University of Brussels and Claude Boutron, Martine Echevin and Claude Lorius Cat the Laboratoire de Glaciologie et Géophysique de l’Environnement in Grenoble). These all failed to obtain reliable data for heavy metals. For example, they could not see the steadily-increasing Pb concentrations in the snow since the 18th century (Boutron and Lorius, 1979). Boutron and Lorius (1979) observed fluxes of Pb, Cd, Cu, Zn and Ag which corresponded approximately to emission fluxes from volcanoes, and believed that volcanoes could account for the enrichment of heavy metals observed in the snow. These findings were challenged by results published by Ng and Patterson (1981) however. These studies generally lacked suitable precautions against sample contamination. During the 1980s and early 1990s a number of important studies were undertaken to resolve the discrepancies of results of Antarctic studies published in the 1970s, largely due to contamination of samples during collection and/or analysis. Boutron, Patterson and co-workers, collaborating closely, published a series of analyses of Pb concentrations in ice cores from several locations in Antarctica (Boutron and Patterson, 1986;1987), confirming the initial results obtained by Patterson and co-workers in 1969 and 1981, and extended the record of lead concentrations in Antarctic ice back to 155,000 years before present.
Table of contents :
Chap. 1- LATE QUATERNARY ENVIRONMENTAL CHANGES AND THE CLIMATE SYSTEM
1.1 The originality of Quaternary climate variability
1.2 Introduction to the climate system
1.3 Paleo-environmental evidences of Quaternary environmental changes
1.4 Climatic tales from EPICA Dome C ice core
References
Chap. 2- TRACE ELEMENTS, TODAY AND IN THE PAST
2.1 History of trace elements production and their use
2.2 Aerosols
2.3 Natural emissions of trace elements into the atmosphere
2.3.1 Mineral aerosols
2.3.2 Sea salt spray
2.3.3 Volcanic aerosols
2.3.4 Biogenic sources
2.4 Anthropogenic emissions of trace elements into the atmosphere
2.5 Atmospheric transport of aerosols
2.6 Literature review
2.6.1 The first reliable evaluation of trace elements concentration in polar snow and ice
2.6.2 Studies of trace elements in Greenland and Antarctica
Chap. 3- IDENTIFICATION OF CRUSTAL TRACE ELEMENTS ORIGIN THROUGH THE RARE EARTH ELEMENTS (REE). LEAD ISOTOPE SIGNATURE
3.1 Global dust emissions at present time
3.2 Principal dust “hot spots” in the Southern Hemisphere
3.3 The dust provenance during glacial periods to the East Antarctic plateau
3.4 The dust provenance during interglacials to the East Antarctic plateau
3.5 REE in sedimentary rocks: influence of provenance
3.5.1 REE properties
3.5.2 REE and provenance studies
3.6 An introduction to the lead isotopic system
3.6.1 Lead properties
3.6.2 Lead concentration and 206Pb/207Pb ratios
3.6.3 The 206Pb/207Pb versus 208Pb/207Pb isotopic ratios
Chap. 4- MERCURY, TODAY AND IN THE PAST
4.1 Mercury properties
4.2 History of mercury production and its use
4.3 Natural release of mercury in the environment
4.4 Biogeochemical cycle of mercury
4.4.1 Atmospheric cycle
4.4.2 Mercury in water and biota
4.4.3 Mercury species in soils and sediments
4.4.4 Mercury in the cryosphere
4.5 Mercury as a global pollutant in remote environment
4.5.1 Studies of mercury in the Arctic: recent studies
4.5.2 Studies of mercury in Antarctica
Chap. 5- ANALYTICAL TECHNIQUES, MATERIALS AND METHODS
5.1 The European Project for Ice Coring in Antarctica (EPICA)
5.2 Samples preparation
5.2.1 Clean conditions
5.2.2 Decontamination procedure
5.3 The Inductively Coupled Plasma Sector Field Mass Spectrometry (ICP-SFMS)
5.3.1 The ICP-SFMS configuration
5.3.2 Spectral interferences
5.4 Study of matrix effects using an ICP-SFMS: Trace elements and Rare Earth Elements
5.4.1 Trace elements
5.4.2 Rare Earth Elements
5.5 Thermal Ionisation Mass Spectrometry (TIMS)
5.5.1 Preparation of the samples for Pb isotopes determination
5.5.2 The TIMS configuration
5.5.3 Isotope dilution mass spectrometry
Chap. 6- RESULTS AND DISCUSSION ABOUT CRUSTAL TRACE ELEMENTS VARIABILITY IN EAST ANTARCTICA OVER THE LATE QUATERNARY
6.1 Concentrations in Antarctic ice back to 670 ky BP
6.2 Comparison between Vostok and Dome C for the past 420 ky BP
6.3 Crustal Enrichment Factors (EFc)
6.4 Crustal trace elements versus climate relationship
6.5 The mid-Brunhes climate shift
6.6 Observed concentrations during the successive interglacials
6.7 Observed concentrations during the successive glacial maxima
Chap. 7- CHANGES IN ATMOSPHERIC HEAVY METALS AND METALLOIDS IN DOME C (EAST ANTARCTICA) ICE BACK TO 671 KY BP
7.1 Changes in concentration during the last eight climatic cycles
7.2 Fallout fluxes for heavy metals and metalloids during the past 671 ky
7.3 Heavy metals and metalloids concentration versus deuterium
7.4 Crustal Enrichment Factors (EFc)
7.5 Contributions from rock and soil dust, sea salt spray and volcanoes
7.6 Principal Components Factor Analyses (PCFA)
7.7 Contribution from Antarctic volcanoes
7.8 Ternary diagrams for glacial maxima and interglacials before and after the Mid-Brunhes
Event (MBE)
Chap. 8- CRUSTAL TRACE ELEMENTS PROVENANCE TROUGH THE REE SIGNATURE FROM 263 TO 671 KY BP IN THE EPICA DOME C ICE CORE
8.1 Concentrations in Antarctic ice back from 263 to 671 ky BP
8.2 Comparison with dust concentration
8.3 Shale-normalized REE pattern
8.4 Comparison of REEUCC from the EPICA/Dome ice core during glacial maxima with REEUCC from potential source areas (PSAs)
8.5 Comparison of REEUCC from the EPICA/Dome ice core during interglacials with REEUCC from potential source areas (PSAs)
CHAP. 9- EIGHT GLACIAL CYCLES OF PB ISOTOPIC COMPOSITIONS IN THE EPICA DOME C ICE CORE
9.1 Sample variability
9.2 Lead and Ba concentrations
9.3 208Pb/207Pb ratios
9.4 Lead isotopic compositions
Chap. 10- INTENSE MERCURY SCAVENGING FROM DUST AND SALT LADEN ANTARCTIC ATMOSPHERE DURING THE GLACIAL AGES
10.1 Materials and Methods
10.2 Changes in concentration during the last eight climatic cycles
10.3 Contributions from natural sources to mercury budget
10.4 Contribution of Hg from the Southern Ocean to the Antarctic during glacial periods
10.5 Insoluble dust versus mercury relationship during coldest climatic stages
10.6 Modeling of the enhanced Hg during the glacial stages
Chap. 11- CONCLUSION AND OUTLOOKS
11.1 Conclusions
11.1.1 Crustal trace elements in the EPICA/Dome C ice core
11.1.2 Metals and Metalloids in the EPICA/Dome C ice core
11.1.3 REE in the EPICA/Dome C ice core
11.1.4 Pb isotopes in the EPICA/Dome C ice core
11.1.5 Mercury species in the EPICA/Dome C ice core
11.2 Outlooks
11.2.1 Metals and Metalloids
11.2.2 Crustal trace elements and Rare Earth Elements
11.2.3 Lead isotopes
11.2.4 Mercury species
References
