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Aix-en-Provence, France

Tisnerat-Laborde N.,French Climate and Environment Sciences Laboratory | Paterne M.,French Climate and Environment Sciences Laboratory | Metivier B.,French Natural History Museum | Arnold M.,CEREGE | And 3 more authors.
Quaternary Science Reviews | Year: 2010

We compiled new 14C analyses of mollusc shells (bivalves and gastropods) of known age from the collection of the Muséum National d'Histoire Naturelle de Paris and previously published data to investigate changes in the sea surface Δ14C and reservoir age in the northeast Atlantic sector (NEA) between 1823 and 1952 AD. The mollusc shells are mainly located off the Atlantic margin between 45°N and 60°N downstream of the North Atlantic Current (NAC). We show that the temporal variability of the NEA Δ14C is independent of the mollusc species, depth habitat, diet and latitudinal distribution. The quasi-null difference between mollusc Δ14C and the marine model indicate that the mollusc Δ14C reflects the Δ14C values of open marine conditions. Between 1823 and 1850 AD, the pre-anthropogenic mean of Δ14C is -45 ± 5‰, corresponding to a reservoir age of 380 ± 60 years and a ΔR value of -7 ± 50 years, in agreement with previous estimates. The Δ14C values show a significant long-term decrease of ∼12‰ from 1823 to 1952 AD attributed to changes in 14C production between 1823 and 1900 AD and the Suess effect between 1900 and 1952 AD.Between 1885 and 1950 AD, Δ14C fluctuations of ∼10‰ up to 18‰ occurred in the northeast Atlantic, corresponding to reservoir age variations of ∼90 years up to 170 years. These fluctuations are very similar to changes of Δ14C in the southern Norwegian Sea. Spectral analyses of the NEA Δ14C exhibit quasi-periodic cycles of about 7.4 years, almost equivalent to the quasi-periodic cycles of the winter index of the North Atlantic Oscillation (NAO) with a period around 6.5 years. We find that changes of NEA Δ14C cannot be attributed to changes in river runoff or the precipitation/evaporation budget. The Δ14C lows (or high reservoir ages) correspond to the more intense phase of the winter NAO, with a time lag of ∼1-3 years. Such a time lag may reflect the eastward transit time of upstream changes originating in the Labrador Sea, then entrained within the NAC along with the subpolar gyre into the northeast Atlantic sector. During these events, we estimate that about 70% of the total transport in the NAC was due to water originating in the Labrador Sea. © 2010 Elsevier Ltd.

Swingedouw D.,French Climate and Environment Sciences Laboratory | Terray L.,European Center for Research and Advanced Training in Scientific Computation | Servonnat J.,French Climate and Environment Sciences Laboratory | Guiot J.,CEREGE
Climate of the Past | Year: 2012

A simulation of the last millennium is compared to a recent spatio-temporal reconstruction of summer temperature over Europe. The focus is on the response to solar forcing over the pre-industrial era. Although the correlation between solar forcing and the reconstruction remains small, the spatial regression over solar forcing shows statistically significant regions. The meridional pattern of this regression is found to be similar in the model and in the reconstruction. This pattern exhibits a large warming over Northern and Mediterranean Europe and a lesser amplitude response over Central and Eastern Europe. The mechanisms explaining this pattern in the simulation are mainly related to evapotranspiration fluxes. It is shown that the evapotranspiration is larger in summer over Central and Eastern Europe when solar forcing increases, while it decreases over the Mediterranean area. The explanation for the evapotranspiration increase over Central and Eastern Europe is found in the increase of winter precipitation there, leading to a soil moisture increase in spring. As a consequence, the evapotranspiration is larger in summer, which leads to an increase in cloud cover over this region, reducing the surface shortwave flux there and leading to less warming. Over the Mediterranean area, the surface shortwave flux increases with solar forcing, the soil becomes dryer and the evapotranspiration is reduced in summer leading to a larger increase in temperature. This effect appears to be overestimated in the model as compared to the reconstruction. Finally, the warming of Northern Europe is related to the albedo feedback due to sea-ice cover retreat with increasing solar forcing. © 2012 Author(s).

Maouche S.,CRAAG | Maouche S.,University of Science and Technology Houari Boumediene | Meghraoui M.,Institute Of Physique Du Globe | Morhange C.,CEREGE | And 3 more authors.
Tectonophysics | Year: 2011

Major uplifts of late Quaternary marine terraces are visible along the coastline of the Tell Atlas of Algeria located along the Africa-Eurasia convergent plate boundary. The active tectonics of this region is associated with large shallow earthquakes (M ≥ 6.5), numerous thrust mechanisms and surface fault-related fold. We conducted a detailed levelling survey of late Pleistocene and Holocene marine notches in the Algiers region that experienced 0.50. m coastal uplift during the 2003 Zemmouri earthquake (Mw 6.8). East of Algiers, Holocene marine indicators show three pre-2003 main notch levels formed in the last 21.9. ka. West of Algiers on the Sahel anticline, the levelling of uplifted marine terraces shows a distinct staircase morphology with successive notches that document the incremental folding uplift during the late Pleistocene and Holocene. The timing of successive uplifts related to past coseismic movements along this coastal region indicates episodic activity during the late Holocene. Modelling of surface deformation in the Zemmouri earthquake area implies a 50-km-long, 20-km-wide, NE-SW trending, SE dipping fault rupture and an average 1.3 m coseismic slip at depth. Further west, the 70-km-long Sahel fold is subdivided in 3 sub-segments and shows ~0.84-1.2 mm/yr uplift rate in the last 120-140. ka. The homogeneous Holocene uplift of marine terraces and the anticline dimensions imply the possible occurrence of large earthquakes with Mw ≥ 7 in the past. The surface deformation and related successive uplifts are modelled to infer the size and characteristics of probable future earthquakes and their seismic hazard implications for the Algiers region. © 2011 Elsevier B.V.

Carpena J.,CEREGE | Lacout J.-L.,ENSIACET
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2010

Synthetic analogues of poor-silicated natural apatites have been doped with uranium. These minerals have been irradiated with a thermal neutron dose in the aim to induce the 235U fission and to obtain a fission track population. Thermal annealing experiments have been performed on the fission track population and allow us to compare the ability of the synthetic minerals to anneal such nuclear damages with their natural analogues. The thermal of the fission tracks in the synthetic minerals need more time and/or higher temperature to reach the same annealing rate as in the natural analogues. The alpha damage present in the natural analogues seems to enhance the thermal annealing of fission tracks. © 2010 Elsevier B.V. All rights reserved.

Rood D.H.,University of California at Santa Barbara | Rood D.H.,Lawrence Livermore National Laboratory | Burbank D.W.,University of California at Santa Barbara | Finkel R.C.,CEREGE | Finkel R.C.,University of California at Berkeley
Quaternary Science Reviews | Year: 2011

We use 10Be surface exposure dating to construct a high-resolution chronology of glacial fluctuations in the Sierra Nevada, California. Most previous studies focused on individual glaciated valleys, whereas our study compares chronologies developed throughout the range to identify regional patterns in the timing of glacier response to major climate changes. Sites throughout the range indicate Last Glacial Maximum retreat at 18.8 ± 1.9 ka (2σ) that suggests rather consistent changes in atmospheric variables, e.g., temperature and precipitation, throughout the range. The penultimate glacial retreat occurred at ca 145 ka. Our data suggest that the Sierra Nevada landscape is dominated by glacial features deposited during marine isotope stage (MIS) 2 and MIS 6. Deposits of previously recognized glaciations between circa 25 and 140 ka, e.g., MIS 4, Tenaya, early Tahoe, cannot be unequivocally identified. The timing of Sierra Nevada glacial retreat correlates well with other regional paleoclimate proxies in the Sierra Nevada, but differs significantly from paleoclimate proxies in other regions. Our dating results indicate that the onset of LGM retreat occurred several thousand years earlier in the Sierra Nevada than some glacial records in the western US. © 2010 Elsevier Ltd.

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