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Montréal, Canada

Magyari E.K.,Eotvos Lorand University | Veres D.,Romanian Academy of Sciences | Wennrich V.,University of Cologne | Wagner B.,University of Cologne | And 10 more authors.
Quaternary Science Reviews | Year: 2014

The Carpathian Mountains were one of the main mountain reserves of the boreal and cool temperate flora during the Last Glacial Maximum (LGM) in East-Central Europe. Previous studies demonstrated Lateglacial vegetation dynamics in this area; however, our knowledge on the LGM vegetation composition is very limited due to the scarcity of suitable sedimentary archives. Here we present a new record of vegetation, fire and lacustrine sedimentation from the youngest volcanic crater of the Carpathians (Lake St Anne, Lacul Sfânta Ana, Szent-Anna-tó) to examine environmental change in this region during the LGM and the subsequent deglaciation. Our record indicates the persistence of boreal forest steppe vegetation (with Pinus, Betula, Salix, Populus and Picea) in the foreland and low mountain zone of the East Carpathians and Juniperus shrubland at higher elevation. We demonstrate attenuated response of the regional vegetation to maximum global cooling. Between ~22,870 and 19,150calyr BP we find increased regional biomass burning that is antagonistic with the global trend. Increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers. We also demonstrate xerophytic steppe expansion directly after the LGM, from ~19,150calyr BP, and regional increase in boreal woodland cover with Pinus and Betula from 16,300calyr BP. Plant macrofossils indicate local (950ma.s.l.) establishment of Betula nana and Betula pubescens at 15,150calyr BP, Pinus sylvestris at 14,700calyr BP and Larix decidua at 12,870calyr BP. Pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the LGM (Fagus sylvatica, Corylus avellana, Fraxinus excelsior). Our sedimentological data also demonstrate intensified aeolian dust accumulation between 26,000 and 20,000calyr BP. © 2014 Elsevier Ltd. Source


Baudron P.,CIRAD - Agricultural Research for Development | Barbecot F.,GEOTOP UQAM | Barbecot F.,University Paris - Sud | Arostegui J.L.G.,Instituto Geologico Y Minero Of Espana | And 4 more authors.
Hydrological Processes | Year: 2014

The development of intense agriculture in semiarid areas modifies intensity and spatial distribution of groundwater recharge by summing irrigation return flow to limited rainfall infiltration. Environmental tracers provide key information, but their interpretation is complicated by more complex groundwater flow patterns. In multilayered aquifers, the real origin of the groundwater samples is hard to assess because of local mixing processes occurring inside long-screened boreholes. We use environmental tracers (14C, 13C, 2H, 18O, 3H) to investigate the long-term evolution of recharge in the five-layer Campo de Cartagena aquifer in South-Eastern Spain, in addition to high-resolution temperature loggings to identify the depth of origin of groundwater. Despite the complex background, this methodology allowed a reliable interpretation of the geochemistry and provided a better understanding of the groundwater flow patterns. The tritium method did not give good quantitative results because of the high variability of the recharge signal but remained an excellent indicator of recent recharge. Nonetheless, both pre-anthropization and post-anthropization recharge regime could be identified and quantified by radiocarbon. Before the development of agriculture, recharge varied from 17mm. year-1 at the mountain ranges to 6mm. year-1 in the plain, whereas the mean annual rainfall is about 300mm. In response to the increase of agricultural activity, recharge fluxes to the plain were amplified and nowadays reach up to 210mm. year-1 in irrigated areas. These values are strengthened by global water budget and local unsaturated zone studies. © 2013 John Wiley & Sons, Ltd. Source


Baudron P.,Fundacion Instituto Euromediterraneo del Agua | Baudron P.,CIRAD - Agricultural Research for Development | Baudron P.,University Paris - Sud | Barbecot F.,GEOTOP UQAM | And 8 more authors.
Radiocarbon | Year: 2013

Radiocarbon decay is rarely used to assess the residence time of modern groundwater due to the low resolution of its long half-life in comparison to the expected range of ages. Nonetheless, the modern 14C peak induced by the nuclear bomb tests traces efficiently the impacts of recent human activities on groundwater recharge, as well as for tritium. A simple lumped parameter model (LPM) was implemented in order to assess the interest of 14C and 3H nuclear peaks in a highly anthropized aquifer system of southeastern Spain under intense agricultural development. It required i) to assess a correction factor for modern 14C activities and ii) to reconstruct the 3H recharge input function, affected by irrigation. In such a complex hydrogeological context, an exponential model did not provide satisfying results for all samples. A better solution was reached by taking into account the qualitative recent variation of the recharge rates into a combined exponential flow and piston flow model. Apart from presenting an uncommon approach for 14C dating of modern groundwater, this study highlights the need of considering not only the variation of the tracer but also the variability of recharge rates in LPMs. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona. Source


Simon Q.,GEOTOP UQAM | Hillaire-Marcel C.,GEOTOP UQAM | St-Onge G.,GEOTOP UQAM | St-Onge G.,Canada Research Chair in Marine Geology | Andrews J.T.,University of Colorado at Boulder
Journal of Quaternary Science | Year: 2014

Precise relationships between high-frequency ice sheet dynamics and late Quaternary climate variability are still poorly understood, notably with regard to their relative timing and causal mechanisms. Baffin Bay is of particular interest in this regard due to the influence of ice streaming activities from the north-eastern Laurentide, southern Innuitian and western Greenland ice margins on its sedimentary regimes during glacial times. Here we document such ice margin dynamics using a sedimentological analysis performed on a piston core from central Baffin Bay and spanning the last 115 ka. Lithofacies analysis and mineralogical assemblages are used to reconstruct sediment sources (using the SedUnMix program) and depositional mechanisms. Coarse detrital carbonate (DC, dolomite-rich) layers are attributed either to north-eastern Laurentide and Innuitian ice stream surges or to pervasive ice rafted debris delivery processes at distinct periods. Out-of-phase fine-grained glaciomarine sediments with a mineralogical signature from western Greenland, linked to Uummannaq ice streaming activity, are interbedded with the coarse DC layers. The new results suggest that during the last glacial cycle, the north-eastern Laurentide and southern Innuitian ice streams were sensitive to high-frequency climate fluctuations, such as the Dansgaard-Oeschger events, while the western Greenland margins were more sensitive to large-scale climatic/oceanic reorganizations, such as relative sea-level changes and/or advection of warmer Atlantic waters into the bay. © 2013 John Wiley & Sons, Ltd. Source


Hillaire-Marcel C.,GEOTOP UQAM | Maccali J.,GEOTOP UQAM | Not C.,GEOTOP UQAM | Not C.,University of Tokyo | Poirier A.,GEOTOP UQAM
Quaternary Science Reviews | Year: 2013

Radiogenic isotopes (Sr, Nd) in Ice Rafted Debris (IRD) sediments from the Lomonosov Ridge and Fram Strait Arctic areas are used to document changes in Arctic sea-ice sources and trajectories since the Last Glacial Maximum (LGM). The two records provide evidence for enhanced sea-ice production in the Beaufort Sea and its subsequent export through Fram Strait during the Younger Dryas (YD) interval. This pattern, exclusive to the YD, followed an LGM-Bølling-Allerød interval, when multiyear and/or reduced sea-ice mobility resulted in sedimentary hiatuses in the Central Arctic. Meanwhile, IRD from Svalbard-Barents ice-sheet margin source were still deposited in the Fram Strait area. The "isotopic excursion" of the YD points to enhanced sea-ice production in the Beaufort Sea, which we link to the Lake Agassiz (?)/Laurentide ice sheet drainage event through the Mackenzie route. Following this event, the Holocene depicts a 5-fold reduction in IRD rates with a shift towards prominent sea-ice production along Russian shelves. From a methodological viewpoint, we demonstrate that radiogenic isotopes must be used in a multi-proxy approach to better constrain IRD and sea-ice sources and routes. From a paleoceanographic perspective, we conclude that an Arctic freshwater/sea-ice export route should now be seen as the most likely mechanism for an AMOC reduction during the YD in accordance with more recent improved model experiment. © 2013 Elsevier Ltd. Source

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