Papers by Martine De angelis
Continuous sea salt and mineral dust aerosol records have been studied on the two EPICA (European... more Continuous sea salt and mineral dust aerosol records have been studied on the two EPICA (European Project for Ice Coring in Antarctica) deep ice cores. The joint use of these records from opposite sides of the East Antarctic plateau allows for an estimate of changes in dust transport and emission intensity as well as for the identification of regional differences in the sea salt aerosol source. The mineral dust flux records at both sites show a strong coherency over the last 150 kyr related to dust emission changes in the glacial Patagonian dust source with three times higher dust fluxes in the Atlantic compared to the Indian Ocean sector of the Southern Ocean (SO). Using a simple conceptual transport model this indicates that transport can explain only 40% of the atmospheric dust concentration changes in Antarctica, while factor 5-10 changes occurred. Accordingly, the main cause for the strong glacial dust flux changes in Antarctica must lie in environmental changes in Patagonia. Dust emissions, hence environmental conditions in Patagonia, were very similar during the last two glacials and interglacials, respectively, despite 2-4 °C warmer temperatures recorded in Antarctica during the penultimate interglacial than today. 2-3 times higher sea salt fluxes found in both ice cores in the glacial compared to the Holocene are difficult to reconcile with a largely unchanged transport intensity and the distant open ocean source. The substantial glacial enhancements in sea salt aerosol fluxes can be readily explained assuming sea ice formation as the main sea salt aerosol source with a significantly larger expansion of (summer) sea ice in the Weddell Sea than in the Indian Ocean sector. During the penultimate interglacial, our sea salt records point to a 50% reduction of winter sea ice coverage compared to the Holocene both in the Indian and Atlantic Ocean sector of the SO. However, from 20 to 80 ka before present sea salt fluxes show only very subdued millennial changes despite pronounced temperature fluctuations, like [...]
Ice Core Studies of Global Biogeochemical Cycles, 1995
Concentration changes occurring for HNO3, HCl and several organic acids in snow recently deposite... more Concentration changes occurring for HNO3, HCl and several organic acids in snow recently deposited over central polar areas have been investigated. These changes, referred to as “post depositional effects”, were studied for time periods varying from one month in Greenland to several tens of years in Antarctica.
Ice Core Studies of Global Biogeochemical Cycles, 1995
A comprehensive study of soluble impurities trapped in Greenland snow layers (Ma+, MH4 +, K+, Mg+... more A comprehensive study of soluble impurities trapped in Greenland snow layers (Ma+, MH4 +, K+, Mg++, Ca++, F-, CH3COO-, C2H3O3 -, HCOO-, CH3SO3 -, Cl-, NO3 -, SO4 - and C2O4 -) has been achieved along a 32.7-m-depth firn Summit (Central Greenland) core which spans the 1908–1989 time period. One of the noticeable feature of these chemical records is the frequent presence of narrow ammonium-rich snow layers in which enhanced concentrations of formate, glycolate, oxalate, and to a lesser extent acetate, are observed. Such a chemical signature has previously been attributed to the long-range transport material from biomass burning at high northern latitudes (Legrand et al, 1992). Identification of microsoot particles by electron microscopy as well as enhancements of black and total carbon concentrations above their background levels by a factor of 2 to 3 and 5 to 6 respectively, in one of these ammonium-rich layers confirm the biomass burning origin of these perturbations. Some association between annual averaged ammonium concentrations of snow layers deposited over the last 80 years in Central Greenland and annual area burned by Canadian forest fires over the past are found. In contrast, a lack of evidence for ammonium perturbation in snow layers deposited in 1915, a particularly dry year with extended forest fires in Siberia, suggests that, even being another large biomass burning circumpolar source, Siberia is not necessarily a major contributor to biomass burning material reaching Central Greenland. The highest ammonium peak revealed by our snow record, which corresponds to the 1908 year, is therefore not necessarily related to the forest fire likely to have occurred in Siberia following the Tunguska meteor fall 30 June 1908.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 2001
X-ray diffraction experiments were carried out on large ice crystals from accreted ice above Lake... more X-ray diffraction experiments were carried out on large ice crystals from accreted ice above Lake Vostok, a subglacial lake lying beneath the East Antarctic ice sheet. Results indicate a surprisingly very low lattice distortion. This crystalline quality does not seem to be affected by impurities. Abnormal grain growth should occur and could explain both the large grain size and the low lattice distortion. Accreted ice is therefore supposed to be non-plastically deforming. These results should be taken into account for further studies of the permeability of accreted ice to drilling fluid present in the borehole. 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS X-ray diffraction / ice monocrystals / Lake Vostok, Antarctica / abnormal grain growth Résumé-Mise en évidence de cristaux d'une grande qualité structurale dans la glace d'accrétion du lac Vostok (Antarctique) par diffraction aux rayons X durs. Des expériences de diffraction de rayons X durs ont été réalisées sur de gros cristaux de glace d'accrétion du lac Vostok, un lac sous-glaciaire qui se situe sous la calotte de l'Antarctique de l'Est. Les résultats indiquent une distorsion du réseau particulièrement faible, attestant une très bonne qualité cristalline qui ne semble pas être affectée par la présence d'impuretés. Le processus de grossissement anormal des grains devrait être à l'origine de la surprenante grande taille et de la qualité cristalline des cristaux de cette glace d'accrétion. Les résultats obtenus nous permettent de supposer que cette glace est très peu déformée plastiquement. Ces résultats devront être pris en compte dans les études sur la perméabilité de la glace d'accrétion au liquide contenu dans le trou de forage. 2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS diffraction X / monocristaux de glace / lac Vostok, Antarctique / grossissement anormal des grains Version abrégée
Special Paper of the Geological Society of America, 1990
Quaternary Science Reviews, 2010
Sulfate (SO 4 2À) and ammonium (NH 4 þ) flux records over the last 150,000 years from both Antarc... more Sulfate (SO 4 2À) and ammonium (NH 4 þ) flux records over the last 150,000 years from both Antarctic EPICA ice cores (European Project for Ice Coring in Antarctica) are presented. The ice core record from Dome C is influenced by the Indian sector of the Southern Ocean (SO), whereas Dronning Maud Land is facing the Atlantic sector. Generally, they reflect the past atmospheric aerosol load and, thus, potentially reveal the fingerprint of marine biogenic sources from the SO. The most important feature of both, the nssSO 4 2À as well as NH 4 þ flux records, is the absence of any significant glacial cycles, in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150,000 years. This finding challenges the iron fertilization hypothesis on long time scales, as the significant changes in dust, e.g. from the last glacial maximum toward the Holocene have neither an impact on nssSO 4 2À nor on NH 4 þ fluxes found in interior Antarctica. The inter-site correlation of both species is weak, r 2 ¼ 0.42 for the nssSO 4 2À flux and r 2 ¼ 0.12 for the NH 4 þ flux respectively, emphasizing the local source characteristics of biogenic aerosol from the SO. Millennial variability in NH 4 þ and nssSO 4 2À is within the uncertainty of our flux estimates. Correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssSO 4 2À flux for the Atlantic sector of the Southern Ocean, but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at EDML.
Journal of Geophysical Research, 2008
The study of past climate variability from ice core investigations has been largely developed bot... more The study of past climate variability from ice core investigations has been largely developed both in polar areas over the past decades and, more recently, in tropical regions, specifically along the South American Andes between 0°and 20°S. However a large gap still remains at mid-latitudes in the Southern Hemisphere. In this framework, a 15.3-m long shallow firn core has been extracted in March 2005 from the summit plateau of Monte San Valentín (3747 m, 46°35 0 S, 73°19 0 W) in the Northern Patagonia Icefield to test its potential for paleoclimate and paleoenvironmental reconstructions. The firn temperature is À11.9°C at 10-m depth allowing to expect well preserved both chemical and isotopic signals, unperturbed by water percolation. The dating of the core, on the basis of a multi-proxy approach combining annual layer counting and radionuclide measurements, shows that past environment and climate can be reconstructed back to the mid-1960s. A mean annual snow accumulation rate of 36 ± 3 cm year À1 (i.e., 19 ± 2 g cm À2 year À1) is inferred, with a snow density varying between 0.35 and 0.6 g cm À3 , which is much lower than accumulation rates previously reported in Patagonia at lower elevations. Here, we present and discuss high-resolution profiles of the isotopic composition of the snow and selected chemical markers. These data provide original information on environmental conditions prevailing over Southern Patagonia in terms of air masses trajectories and origins and biogeochemical reservoirs. Our main conclusion is that the San Valentín site is not only influenced by air masses originating from the southern Pacific and directly transported by the prevailing west winds but also by inputs from South American continental sources from the E-NE, sometimes mixed with circumpolar aged air masses, the relative influence of these two very distinct source areas changing at the interannual timescale. Thus this site should offer a wealth of information regarding (South) Pacific, Argentinian NE-E areas and Antarctic climate variability.
Journal of Geophysical Research: Atmospheres, 1995
Central Greenland and East Antarctic ice cores have been studied to investigate the carboxylic ac... more Central Greenland and East Antarctic ice cores have been studied to investigate the carboxylic acid (acetate, CH3COO-; formate, HCOO-; glycolate, C2H303-; and oxalate, C204-) content of high-latitude precipitation. The two records cover the end of the last glacial age, the last great climatic change having occurred between 10,000 and 15,000 years B.P., and the Holocene period which started some 10,000 years ago. Carboxylic acids were measured using ion chromatography. These measurements are more difficult and require more stringent precautions to prevent sample contamination than inorganic trace species measurements. Carboxylic acids account for up to 25% of the free acidity in Greenland and are one order of magnitude more abundant in Greenland than in Antarctic precipitation. In Greenland precipitation deposited under present climatic conditions, formic and acetic acids are both present at the 10 ng g-• level and are the most abundant carboxylic acids, while glycolic and oxalic acids with concentrations close to 1 ng g-• represent minor carboxylic acid species. The level of formic, and to a lesser extent acetic, acid is also found to be strongly pH dependent. There is less formic acid at depths corresponding to periods when the acidity of the atmosphere was enhanced by a volcanic activity. Over the last 12,700 years, the carboxylic acid level of Greenland precipitation has often been sporadically enhanced by several orders of magnitude. Such large perturbations, which are accompanied by large increases of NH4 + concentrations, are probably caused by biomass-burning events which occurred at high northern latitudes. A particular chemical feature appears in snow layers corresponding to biomass-burning events which occurred during the Younger Dryas (11,550 to 12,700 years B.P.). During this cold stage, the precipitation was alkaline and the events were accompanied by an input of nitrite suggesting that peroxyacetyl nitrate (PAN) was present in the atmosphere and was hydrolyzed in alkaline cloud water. Formate and acetate profiles indicate that background levels of these carboxylic acids were 5 and 2 times lower, respectively, during the last glacial maximum (15,000 to 34,000 years B.P.) than during the Holocene stage in Greenland precipitation. The increases of the acetate and formate snow contents in response to the glacial-interglacial climatic transition exhibit a time lag of some 5000 years. In particular, the formic acid increase follows perfectly the timing of the retreat of the Laurentide ice sheet from 18,000 years B.P. to the mid-Holocene stage (6000 years B.P.). Our data suggest therefore that carboxylic acids in Greenland precipitation are mainly linked to emissions from the high-latitude continental biosphere. In contrast, the incloud oxidation of formaldehyde produced from methane oxidation under acidic conditions likely represents the main source of formic acid in East Antarctica. Finally, the study of recent Greenland snow deposits indicates that the expected trend of carboxylic acid concentrations due to man-made activities is counteracted by a simultaneous increase of the acidity related to growing fossil fuel combustion, which leads to a less efficient uptake of carboxylic acids into precipitation.
Journal of Geophysical Research: Oceans, 1997
Selected segments from the Eemian period of the Greenland Ice Core Project (GRIP) core from Summi... more Selected segments from the Eemian period of the Greenland Ice Core Project (GRIP) core from Summit, Greenland, have been analyzed by ion chromatography and Coulter Multisizer. The results will be discussed with special emphasis on the sudden cooling events, event 1 and event 2, in the record as observed in the •SO profile [GRIP members, 1993; Dansgaard et al., 1993]. Whether the sudden cooling events of the Eemian represent a real climatic signal or they are a consequence of disturbed ice core stratigraphy is still a matter of debate [Chappellaz et al., this issue]. However, several features of the chemical profiles across these cooling events are difficult to explain if they were a result of disturbed stratigraphy. We will focus our discussion on the unique profiles of nitrate, methane sulfonic acid (MSA), and ammonium across event 1 and argue that even if we allow for movement of ions by diffusion or displacement of ions by physical or chemical interactions, events 1 and 2 are not likely to consist of ice from other climatic periods which have been inserted in the Eemian strata by folding processes. Furthermore, our records do not show any layers in the vicinity of the Eemian strata which can be a possible source of the ice in event 1. We believe that the events represent a climate signal, and we will discuss other possible explanations of the profiles. Our conclusion that the cold events in the Eemian represent a real climatic signal runs counter to other evidence from gas measurements. However, whatever their cause, the unusual chemical signals require further discussion and explanation.
Journal of Geophysical Research, 2003
Chloride (Cl À) and sodium (Na +) in ice cores originate mainly from sea salt, and one would thus... more Chloride (Cl À) and sodium (Na +) in ice cores originate mainly from sea salt, and one would thus expect the Cl À /Na + ratio to reflect the seawater ratio. However, at Dome C, a low-accumulation site in East Antarctica, this is not the case in present-day snow. Instead, a Cl À excess relative to Na + is observed in surface snow, and within a few meters depth the Cl À concentration decreases, and the Cl À /Na + ratio becomes significantly lower than the seawater ratio. Aerosol studies at coastal Antarctic sites have shown that the reaction of sea-salt aerosols with nitric and sulphuric acid leads to the formation of HCl that eventually escapes the sea-salt aerosol. The observed decrease in Cl À concentrations in the uppermost snow layers is due to reemission of HCl from the snow. Postdepositional loss of HCl depends among other factors on the accumulation rate at the site, with lower accumulation rates leading to larger losses. During the Last Glacial Maximum (LGM) the Cl À /Na + ratio is relatively stable and close to the seawater ratio, despite the even lower accumulation rate during that time. The likely explanation for this conflicting observation is that high levels of dust neutralized nitric and sulphuric acids during the LGM which in turn reduced the formation of HCl from sea-salt aerosol. With less or no HCl formed, postdepositional loss would be prevented, keeping the Cl À /Na + ratio close to that of sea water.
Journal of Geophysical Research: Atmospheres, 2002
Sulfur isotopes of sulfate have been measured in a discontinuous set of polar ice core samples fr... more Sulfur isotopes of sulfate have been measured in a discontinuous set of polar ice core samples from Summit, central Greenland, covering the preindustrial (from the fourteenth to the eighteenth century) and industrial (from 1872 to 1969 A.D.) periods. Results have been used to estimate the different source contributions to the deposited sulfate and their evolution along the last centuries. They indicate that the preindustrial background sulfate budget is slightly dominated on a year-round average by marine biogenic emissions, amounting to close to half of the non-sea-salt sulfate (49%). The second contribution is provided by continental sources of secondary sulfate, including background volcanism and, to a lesser extent, continental biota (44% of the non-sea-salt sulfate). Sulfur emitted by relatively weak eruptions is found to be largely depleted in 34 S compared to bulk volcanic S, suggesting an efficient washout of the heavier isotope during the tropospheric transport. The impact of human-driven emissions on the sulfate deposited in central Greenland ice is visible in isotope data as early as 1870 A.D. The isotopic signature of anthropogenic sulfur deposited during the twentieth century is found to be constant (d 34 S % + 3.0 ± 1.5%), regardless of the changes of dominant source regions and emission processes. This signature is slightly but measurably lighter than the one reported for Arctic haze pollution events.
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Papers by Martine De angelis