Late Holocene volcanic and anthropogenic mercury deposition in the western Central Andes (Lake Chungara, Chile)

Volcanismis one of the major natural processes emitting mercury (Hg) to the atmosphere, representing a significant component of the global Hg budget. The importance of volcanic eruptions for local-scale Hg deposition was investigated using analyses of Hg, inorganic elemental tracers, and organic biomarkers in a sediment sequence from Lake Chungara (4520 m a.s.l.). Environmental change and Hg deposition in the immediate vicinity of the Parinacota volcano were reconstructed over the last 2700 years, encompassing the pre-anthropogenic and anthropogenic periods. Twenty eruptions delivering large amounts of Hg (1 to 457 mu g Hg m(-2) yr(-1) deposited at the timescale of the event) were locally recorded. Peaks of Hg concentration recorded after most of the eruptions were attributed to a decrease in sedimentation rate together with the rapid re-oxidation of gaseous elemental Hg and deposition with fine particles and incorporation into lake primary producers. Over the study period, the contribution of volcanic emissions has been estimated as 32% of the total Hg input to the lake. Sharp depletions in primary production occurred at each eruption, likely resulting from massive volcaniclastic inputs and changes in the lake-water physico-chemistry. Excluding the volcanic deposition periods, Hg accumulation rates rose from natural background values (1.9 +/- 0.5 mu g m(-2) yr(-1)) by a factor of 2.3 during the pre-colonial mining period (1400-900 yr cal. BP), and by a factor of 6 and 7.6, respectively, during the Hispanic colonial epoch (400-150 yr cal. BP) and the industrial era (similar to 140 yr cal. BP to present). Altogether, the dataset indicates that lake primary production has been the main, but not limiting, carrier for Hg to the sediment. Volcanic activity and climate change are only secondary drivers of local Hg deposition relative to the magnitude of regional and global anthropogenic emissions

Un enregistreur quaternaire souterrain de l’environnement exokarstique et endokarstique : le cône d’entrée de l’aven d'Orgnac (Ardèche, France).

PosterInternational audienc

Investigating the excavated coloured rocks (‘ochres’) from Nawarla Gabarmang, a c. 48,000 year old Aboriginal site in northern Australia

PosterInternational audienc

Holocene vegetation, climate and human impact in steppes around Lake Sevan (Armenia) based on a multiproxy approach: Pollen, NPPs and brGDGTs

International audience<p>In the Caucasus Mountains, the role of human influences and climate changes on steppes expansion over the Holocene is still discussed because this region is poorly documented. This study investigates (1) modern pollen-vegetation relationships in Armenia and (2) changes in vegetation, human activity and climate in the Holocene record of Vanevan peat (south-eastern shore of Lake Sevan) located in Armenia. The last 9700 years are recorded in the Vanevan core. We used a multiproxy approach including XRF, Pollen, Non-Pollen Palynomorphs (NPPs) and branched glycerol dialkyl glycerol tetraethers (brGDGTs) to reconstruct changes in vegetation, human impact and climate. The combination of these proxies is innovative and aims to distinguish the impact of human activities and climate change on vegetation. Modern pollen assemblages from semi-desert/steppe regions of Armenia show an abundance of Chenopodiaceae while meadows steppes, subalpine and alpine meadows are dominated by Poaceae. The Holocene vegetation at Vanevan is characterized by steppes dominated by Poaceae, <em>Artemisia</em> and Chenopodiaceae. However, several arboreal taxa, such as <em>Quercus, Betula, Carpinus betulus</em> and <em>Ulmus</em>, are more developed on slopes between 8600 and 5100 cal BP. Regarding the human impact, the presence of agriculture is attested since 5200 cal BP, largely increases during the last 2000 years cal BP (high percentages of <em>Cerealia</em>-type pollen) and correlates with the occupation periods reported in archeological studies. Palaeoclimate changes at Vanevan are estimated from (1) water level changes (2) temperature reconstructions based on brGDGTs (3) climate reconstructions based on pollen (through a multi-method approach: Modern Analogue Technique, Weighted Averaging Partial Least Squares regression, Random Forest, and Boosted Regression Trees). Climate reconstructions based on pollen and brGDGTs are rare and the multi-method approach using pollen data is innovative in the region. The results of Vanevan give evidence of high temperatures from 7900 to 5100 cal BP and arid events at 6000, 5000-4500 and 4200 cal BP, in agreement with other regional records.</p&gt

Determining natural versus cultural coloured rocks (‘pigments’) at Nawarla Gabarnmang, a 48,000-50,000 year old Aboriginal site in northern Australia

International audienc

A high-resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania)

Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history

Early human impact on soils and hydro-sedimentary systems: Multi-proxy geoarchaeological analyses from La Narse de la Sauvetat (France)

International audienceWe analysed the late-Holocene pedo-sedimentary archives of La Narse de la Sauvetat, a hydromorphic depression in the southern Limagne plain (central France), where chronologically accurate studies are scarce. The multi-proxy geoarchaeological and palaeoenvironmental analysis of two cores from different areas of the basin was carried out through sedimentological, geochemical, micromorphological and malacological investigations. Integration of these datasets supported by a robust radiocarbon-based chronology allowed discussion of socio-environmental interactions and anthropogenic impacts from Late Neolithic to Early Middle Ages. Until the Middle Bronze Age, there was no clear evidence of anthropogenic impact on soils and hydro-sedimentary dynamics of the catchment, but two peaks of high alluvial activity probably related to the 4.2 and 3.5 kyr. BP climate events were first recorded in Limagne. Significant anthropogenic impacts started in the Late Bronze Age with increased erosion of the surrounding volcanic slopes. However, a major threshold was reached c. 2600 cal BP with a sharp increase in the catchment erosion interpreted as resulting from strong anthropogenic environmental changes related to agricultural activities and drainage. This implies an anthropogenic forcing on soils and hydro-sedimentary systems much earlier than was usually considered in Limagne. These impacts then gradually increased during Late Iron Age and Roman periods, but environmental effects were certainly contained by progress in agricultural management. Late Antiquity environmental changes are consistent with regional trend to drainage deterioration in lowlands, but marked asynchrony in this landscape change suggests that societal factors implying differential land management were certainly predominant here