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An article in the special issue "Quantification of human–environment interactions in the past" comprising 8 articles (plus the introduction). This special issue is a contribution to PAGES' Focus 4 (human–climate–ecosystem interactions) theme and specifically the Land Use and Cover Soil and Sediment and Water Themes which ran up until 2014. The volume emerged from the PAGES supported meeting: ‘Towards a more accurate quantification of human–environment interactions in the past’ held in Leuven Belgium from 3–7 February 2014. ABSTRACT: This study combines a traditional qualitative description of sedimentary units with a quantitative sediment budget approach to document the colluvial and alluvial sediment dynamics in the Valdaine region (Drôme France) from the Iron Age to the early medieval period (700 BC–900 AD). Three transects through colluvial and alluvial deposits are discussed in detail to demonstrate the way in which absolute dating techniques and archeological evidence are combined to establish a stratigraphic framework. This framework is applied to 16 sites and further combined with an existing sediment budget to quantitatively reconstruct the catchment wide sedimentary evolution. Results show large variations over time in sediment deposition: a first phase from 700 to 400/300 BC followed by an incision phase between 300/200 BC and 100/50 BC an unprecedented peak in deposition during the Roman period (100/50 BC–450 AD) with continued but decreased deposition from 450 to 900 AD. These results show how sediment deposition relates to increased population density and anthropogenic land use on a timescale of a few centuries. The analysis indicates important erosion and deposition phases during the Roman period considered to be a warmer period (Roman warm period). A relation to particular regional climate variations could not be discovered possibly because of the temporal resolution of the sedimentological data that still fail to identify events lasting a few decades to a century.

Peatlands, wetlands with > 30 cm of organic sediment, cover more than 3 x 106 km2 of the earth surface and have been accumulating carbon and sediments throughout the Holocene. The location of peatland formation and accumulation has been dynamic over time, as peat formation in areas like Alaska and the West Siberian Lowlands preceded peat formation in Fennoscandia and Eastern North America due to more favorable climate for peat formation. Using the geographic distribution of peatlands in the past can indicate general climatic conditions, including hydroclimate, given that the underlying geology is well understood. Peatlands form under a variety of climatic conditions and landscape positions but do not persist under arid conditions, instead requiring either humid conditions or cold temperatures. However, peatlands may have existed in the past in areas not currently suitable for peatland formation and persistence, but where peats can be found at depth within the sediment column. Here we map the locations of histic paleosols, relict peat, and buried peats since the Last Glacial Maximum using a compilation of sites from previous studies. We compare these records of past peatland distribution to present-day peatland distribution. We evaluate regional differences in timing of peatland development in these buried peatlands to the development of extant peatlands. Finally, we compare the timing of past peatland extent to the to modeled paleoclimate during the Quaternary. In addition to implications for paleoclimate, these past peatlands are not well accounted for in present-day soil carbon stocks but could be an important component of deep soil carbon pools.

International audience

Fluvial architecture changed under the influence of increasing human impact throughout the Holocene in many north-west European catchments. Typically, peat formation - in a marshy environment during the Early and Middle Holocene - is replaced by clastic overbank deposition. In this study we show the importance of a detailed chronology of floodplain changes, with an example from the Belgian Dijle catchment. In total, 45 radiocarbon ages from 15 alluvial sites were used. Cumulative probability functions were made of the radiocarbon ages from the base (16 samples) and top (29 samples) of the peat layer. Two alluvial sites were studied in detail. The results indicate that the end of peat growth and the transition towards clastic overbank deposition is diachronous at the catchment scale, ranging between 6500 and 500 cal a BP. This diachronous pattern can be attributed to differences in timing and intensity of agricultural activities at the catchment scale, or to differences in hillslope-floodplain connectivity. Moreover, in the broad floodplain of the main valley, the top of the peat layer is even diachronous at cross-section scale. These results indicate that inferences on changes in sedimentation rate and floodplain changes should be based on a multi-transect and multi-core dating approach. © 2014 John Wiley & Sons, Ltd. ispartof: Journal of Quaternary Science vol:29 issue:4 pages:351-360 status: published

International audience

We address the enhancement of orange-light luminescence of Mn-doped zinc sulfide nanoparticles (NPs) induced by exposure to UV light. Ultrafine ZnS:Mn NPs are prepared by microwave-assisted crystal growth in ethanol, without adding any dispersant agents. When exposed to UV light, their orange emission intensity undergoes a strong increase. This effect is observed when the NPs are deposited as a thin layer on a transparent substrate or dispersed in an ethanolic suspension. Such a feature was already observed on polymer- or surfactant-coated ZnS:Mn NPs and explained as a passivation effect. In this study, by coupling X-ray photoelectron, Fourier transform infrared, and electron paramagnetic resonance spectroscopy, we establish that this photoactivated luminescence is rather the consequence of lattice-strain effects. Indeed, our data show that UV irradiation in air promotes surface oxidation, replacing the outer sulfide layer with a sulfate one. The mismatch between the resulting outer crystallographic metal sulfate lattice and the inner sulfide one induces mechanical strains on the latter, thus partially relaxing the selection rules controlling the electronic transition from the 4T1 to the 6A1 molecular states of [MnS4]6- emitting centers. These results are relevant because they shed light on the long controversial discussions on the origin of the photoactivated phosphorescence in such systems.