Radiocarbon dating, pollen and non-pollen palynomorph analyses from a lake core were used to establish the timing and effects of farming activities around Lake Igaliku, Eastern Settlement, Greenland. The absence of agro-pastoral impact before the medieval colonization by Europeans provides an opportunity to understand the development of farming activity in a pristine landscape. The results show that the first phase of clearance and grazing pressure, without the expansion of the Norse apophyte (native plant, in habitats created by humans) Rumex acetosa type, could have occurred in the 9-10th century A.D. The presence of Norse settlers and livestock is clearly recorded from the 11-12th century A.D. with increasing frequencies of the Norse apophytes Rumex acetosa type and Ranunculus acris type, and coprophilous fungi. This colonization phase is followed by a period of decreasing human impact at the beginning of the 14th century, with a decrease in weeds, apophytes and coprophilous fungi suggesting a reduced grazing pressure. The regrowth of Salix and Betula and the disappearance of anthropogenic indicators except Rumex acetosa type between the 15th and 18th century demonstrate the abandonment of the settlement, until the development of contemporary agriculture in the 20th century.

Assessing the extent to which changes in lacustrine biodiversity are affected by anthropogenic or climatic forces requires extensive palaeolimnological data. We used high-throughput sequencing to generate time-series data encompassing over 2200 years of microbial eukaryotes (protists and Fungi) diversity changes from the sedimentary DNA record of two lakes (Lake Bourget in French Alps and Lake Igaliku in Greenland). From 176 samples, we sequenced a large diversity of microbial eukaryotes, with a total 16 386 operational taxonomic units distributed within 50 phylogenetic groups. Thus, microbial groups, such as Chlorophyta, Dinophyceae, Haptophyceae and Ciliophora, that were not previously considered in lacustrine sediment record analyses appeared to be potential biological markers of trophic status changes. Our data suggest that shifts in relative abundance of extant species, including shifts between rare and abundant taxa, drive ecosystem responses to local and global environmental changes. Community structure shift events were concomitant with major climate variations (more particularly in Lake Igaliku). However, this study shows that the impacts of climatic fluctuations may be overpassed by the high-magnitude eutrophication impacts, as observed in the eutrophicated Lake Bourget. Overall, our data show that DNA preserved in sediment constitutes a precious archive of information on past biodiversity changes.

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This is the first integrated multiproxy study to investigate climate, catchment evolution and lake ecology in South Greenland. A 4-m-long sedimentary sequence from Lake Igaliku (618 00 0 N, 458 26 0 W, 15 m asl) documents major environmental and climatic changes in south Greenland during the last 10 ka. The chronology is based on a 210 Pb and 137 Cs profile and 28 radiocarbon dates. The paleoenvironmental history is interpreted on the basis of magnetic susceptibility, grain size, total organic carbon, total nitrogen and sulphur, sedimentation rates, pollen, and diatom assemblages. The basal radiocarbon date at ca. 10 cal ka BP provides a minimum age for the deglaciation of the basin, which is followed by *500 years of high sedimentation rates in a glaciomarine environment. After the glacio-isostatic emergence of the basin ca. 9.5 cal ka BP, limnological and terrestrial proxies suggests early warmth, which may have been interrupted by a cold, dry and windy period between 8.6 and 8.1 cal ka BP. A dry and windy event *5.3-4.8 cal ka BP preceded the Neoglacial transition at Lake Igaliku, which is characterized by a shift toward moister and perhaps cooler conditions *4.8 cal ka BP, causing major changes in terrestrial and aquatic ecological conditions. Significant cooling is documented after *3 cal ka BP. Since *1 cal ka BP the climatic-driven changes were overprinted by the human influence of Norse and recent agriculture.

Two peat sequences were sampled in the vicinity of the main mining districts of the Vosges Mountains: Sainte-Marie-aux-Mines and Plancher-les-Mines. Lead isotopic compositions and excess lead fluxes were calculated for each of these radiocarbon-dated sequences. Geochemical records are in very good agreement with the mining history of the area, well known over the last millennium. Except for an anomaly corresponding to the Middle Bronze Age which has not yet been resolved, there is no clear geochemical evidence of local metal production in the Vosges before the 10th century as excess lead deposition archived between 500 BC and 500 AD is attributed to long-range transport of polluted particulate matter. The approach described here can be applied to other mining districts where archaeological evidence is scarce or even lacking, but where past exploitation is suspected

International audienc

Terra Nova, 00, 1–8, 2010 Abstract The present tectonic activity of the Jura fold‐and‐thrust belt is a matter of scientific debate. At its north‐western front, differentially uplifted palaeo‐meanders of the Doubs River record Late Quaternary growth of the Citadelle Anticline, associated with a minimum rock uplift of 13 m. Local rock uplift rates estimated from optical stimulated luminescence dating of oxbow lake deposits measure 0.17 ± 0.05 mm per annum. Reconstruction of the deformation history reveals that buckling took place simultaneously with focused Pleistocene river incision. The structural, geomorphic and temporal setting suggests that active deformation could possibly be sustained by incision‐related erosion. These observations shed new light on the modes of recent deformation in the Jura Mountains and on the present‐day dynamics of the Alpine orogenic front.

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