As a part of a wider study aimed at determining new molecular biomarkers in soils and sediments that could be specific of distinct vegetation types with respect to unravelling past changes in land use, we analysed the neutral lipid content of soil developed in the catchment of a small lake in central France. The ketone/acetate lipid fraction of soil under pasture or meadow contains a series of pentacyclic triterpenyl acetates of wide structural diversity, most being reported in soil for the first time. The restricted number of potential plant sources of triterpenyl acetates (some produced by a single species) underlines the potential of triterpenyl acetates as new biomarkers to track past vegetation change in palaeoenvironmental studies, when found in natural archives such as soil, sediments or peat.

International audienceNortheast Brazil represents a key area in terms of Holocene environmental changes in South America due to its distinct semi-arid climate at near equatorial latitudes as well as to a wetter Early and Middle Holocene paleoclimate in comparison with other South America regions, which also experienced a reduced monsoon at that time. We studied the lacustrine sediments of Lake Boqueirão, which is located at 5°S latitude on the Brazilian Atlantic coast; it is directly influenced by displacement of the Intertropical Convergence Zone (ITCZ). A short (1 m) core "Boqc0701" was collected at a 7.5 m water depth during a seismic survey. Organic matter (OM) geochemical [Rock Eval Total Organic Carbon (TOC), Hydrogen Index (HI), Oxygen Index (OI)] and petrographical studies allowed us to distinguish five sedimentary intervals during the last 3 kyrs. Phase E (3000 to 2050 cal yr BP) presents the largest TOC, HI and OI fluctuations in the entire core. The most probable cause of these variations is a great instability in the lake level during this period. Phase D (2050 to 1830 cal yr BP) is marked by an increase in sedimentation rate and a higher contribution from a well-preserved OM with an algal origin; this was interpreted as a higher and more stable lake level. During phase C (1830 to 1550 cal yrs BP), low HI and high OI indicate the input of more oxidized, degraded and detrital OM, reflecting a lower lake level. In phase B (1550 to 1470 cal yr BP), the OM quality and quantity (HI and TOC) indicate an algal contribution. During phase A (1470 to 570 cal yr BP), the high stability of the proxies may be due to a deep environment where OM fluctuations are strongly buffered. These changes in lake level can be compared with other tropical South America high resolution records. A correspondence seems to exist between phases of low ENSO, cool North Atlantic Ocean and Boqueirão wet phases. We did not encounter this same pattern during the last 1050 years, during which the 1050-570 cal yrs BP interval was generally wet (although probable fluctuations are buffered in our proxies) while the North Atlantic was warm (Mann et al., 2009). A prolonged dryness occurred in Lake Boqueirão from 570 cal yrs BP until recent decades. This phase corresponds to the Little Ice Age characterized by a cooler North Atlantic Ocean (Mann et al., 2009). These data indicate that the teleconnection pattern between the tropical Atlantic, ENSO and Northeast Brazil rainfalls has changed in the past

A multi-proxy study has been performed on a sediment core from the Curuai floodplain, Central Amazonia. The combination of elemental, isotopic and molecular analysis of a 110 cm core (a record of ca. the last 100 yr) allowed reconstruction of the hydrological conditions of organic matter (OM) deposition. Two units could be delineated. The first (UI) was composed of three sub-units: UIa (0-15 cm), composed of highly degraded organic particles originating from the surrounding soil and indicative of restricted transport; UIb (15-48 cm), during which the region was permanently flooded and the material stored came from soil runoff, mainly from alluvial forest; and UIc (48-88 cm) composed of material from Amazon River suspended sediment, itself originating from OM degradation in forest soil. In UII (88-111 cm), the OM originated mainly from the forest soil and other plant remains in the floodplain. The data reveal that, during the four distinct depositional periods, the sedimentary OM alternated between land derived soil and alluvial vegetation due to changes in hydrodynamics.

International audiencePurpose: Eighteen soils were sampled in the Lake Aydat catchment in order to analyse free fatty acid (FA) content; FAs are considered to be among the most amenable biomarkers to mobilisation by runoff waters. The majority of the study area has soil cover consisting of grasslands or forest since the 2nd World War, although some covers having changed more recently. Material and methods: The soil studied all developed on volcanic rocks (andisols). The bulk organic matter (OM) content of the samples was characterized by Rock-Eval (RE) pyrolysis. The FAs were determined by gas chromatography-mass spectrometry (GC-MS) analysis of isolated and derivatized (methylation and trimethylsilylation) FA fractions. Results and discussion: Few low molecular weight compounds (LMW; i.e.

International audienceTo reconstruct the evolution of livestock in SW Greenland over the last two millennia, we measured the concentration of bile acids in a sedimentary sequence retrieved from Lake Igaliku. Deoxycholic acid (DOC) was the sole bile acid. and was present throughout the sequence.The DOC flux correlated quantitatively with that of coprophilous fungal spores. Maximum DOC and coprophilous fungal spores fluxe was recorded during the two periods of human settlement and grazing activity in the region (i.e. the Norse settlement during the Middle Ages and the recent Danish agricultural phase since 1920). These flux values were consistent with the presence of recent livestock around the lake and are attested to by way of archaeological data relating to the Norse period. In contrast, the DOC and coprophilous fungal spores background during pre-Norse times and the Little Ice Age (LIA), indicated the presence of wild herbivores. Lower DOC and coprophilous fungal spore fluxes values after the Norse abandonment, compared with pre-colonization conditions, could indicate that Norse activity in conjunction with climate pejoration, altered durably the pristine wildlife.Therefore, these quantitative correlations between DOC and coprophilous fungal spores fluxes potentially suggest a quantitative relationship with the livestock grazing in the catchment. The comparison between sedimentary DOC and coprophilous fungal spores provides tremendous highlights on past pastoral dynamics over the last 2000 yr in SW Greenland

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International audiencePaleoenvironmental studies previously performed on Lake Igaliku revealed two agropastoral phases in south Greenland: the Norse settlement from AD 986 to ca. AD 1450 and the recent installation of sheep farmers, since the 1920s. To improve the knowledge of the timing and magnitude of the Greenlandic agropastoral activities, a lipid inventory was realized and compared with biological and geochemical data. During the 12th century, a major increase in deoxycholic acid (DOC) and coprophilous fungal spores revealed a maximum of herbivores. Synchronously, a minimum of the n-C29/n-C31 alkane ratio and tree and shrub pollen and a maximum of triterpenyl acetates showed a reduction in the tree and shrub cover, because of grazing activities. Lupanone, produced by angiosperms, appeared simultaneously in the molecular content, probably revealing an introduction of plant species by the Norse, as it has been the case for Rumex spp. No major erosion was recorded by trimethyl-tetrahydrocrysenes (TTHCs) and titanium (Ti) fluxes. No massive algal production, identified by the n-C17/total n-alkane ratio and mesotrophic diatoms, was either revealed. After the Norse abandon (around AD 1450), a return of the vegetation to quasi-pristine conditions was observed in the molecular content. Finally, a re-introduction of sheep in the 1920s provoked major impacts between the 1970s and the 1990s. A major decrease in the n-C29/n-C31 alkane ratio and tree and shrub pollen associated with maxima of triterpenyl acetates, TTHCs, Ti fluxes, and mesotrophic diatoms highlighted a reduction in the tree and shrub cover, a strong soil mobilization, and algal blooms, probably linking to the recent mechanized creation of hay fields and the massive use of fertilizers. In this study, molecular biomarkers revealed two periods of major impacts: the 12th century and between the 1970s and the 1990s, separated by centuries without agropastoral practices, allowing a quasi-resilience of the vegetation