Papers by Nicolas Thouveny
Rock magnetic properties and radiocarbon dates of samples obtained on Ile de Possession, South Indian Ocean, supplement to: Van der Putten, Nathalie; Hébrard, Jean-Pierre; Verbruggen, Cyriel; Van de Vijver, Bart; Disnar, J R; Spassov, S; de Beaulieu, Jacques-Louis; De Dapper, M; Keravis, D; Hus, ...
A 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possessi... more A 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possession (Iles Crozet), has been investigated, based on a multi-proxy approach. The methods applied are macrobotanical (mosses, seeds and fruits) and diatom analyses, complemented by geochemical (Rock-Eval6) and rock magnetic measurements. The chronology of the core is based on 5 radiocarbon dates. When combining all the proxy data the following changes could be inferred. From the onset of the peat formation (6200 cal yr BP) until ca. 5550 cal yr BP, biological production was high and climatic conditions must have been relatively warm. At ca. 5550 cal yr BP a shift to low biological production occurred, lasting until ca. 4600 cal yr BP. During this period the organic matter is well preserved, pointing to a cold and/or wet environment. At ca. 4600 cal yr BP, biological production increased again. From ca. 4600 cal yr BP until ca. 4100 cal yr BP a 'hollow and hummock' micro topography de...
Kukla G.J., Beaulieu J.-L. de, Svobodova H., Andrieu-Ponel V., Thouveny N. & Stockausen H., 2002. Tentative Correlation of Pollen Records of the Last Interglacial at Grande Pile and Ribains with Marine Isotope Stages. Quaternary Research. 58, 32-35
Earth and Planetary Science Letters, 2020
Be/ 9 Be ratio (Be ratio) relative paleointensity (RPI) lock-in depth geomagnetic dipole moment (... more Be/ 9 Be ratio (Be ratio) relative paleointensity (RPI) lock-in depth geomagnetic dipole moment (GDM) atmospheric 10 Be production Documenting accurately amplitude and rhythms of geomagnetic variations is a prerequisite to understand the mechanisms triggering geomagnetic excursions and reversals. We present new authigenic 10 Be/ 9 Be ratio (Be ratio) results covering the 60-20 ka time interval from equatorial core MD05-2920. The most significant Be ratio peak is located 18 cm above the main relative paleointensity (RPI) minimum recorded in this sequence. These are interpreted as two independent recordings of the geomagnetic dipole moment (GDM) decrease linked to the Laschamp excursion dated at ca 41 ka. The stratigraphic offset is assignable to post-depositional magnetization lock-in processes resulting in time delay of 1.6 ka. The Be ratio and RPI records show comparable asymmetric behavior before and after the dipole low. The Be ratio record is combined with three other series to construct a global record of 10 Be paleoproduction variations. This compilation demonstrates the strong coherence of low and mid latitudes data sets and its comparison with 10 Be-flux records from polar regions fully supports the hypothesis of a global atmospheric 10 Be production doubling during the Laschamp. The Be ratio stack is converted in terms of GDM using both a theoretical model and a reconstruction of GDM values using absolute paleointensities measured on lava flows. Both methods provide similar results. The dipole moment record derived from this approach (BeDM 20-60 ) shows the following characteristics: high field values (> 11 × 10 22 Am 2 ) prior to a sharp two-steps dipole decrease until reaching minimum values (1.8 ± 0.7 × 10 22 Am 2 ) between 41.6 and 40.9 ka at the time of the Laschamp excursion. The GDM partly recovers up to values of ∼ 6.3 × 10 22 Am 2 , and oscillates in this range, without showing any sharp decreases that could be associated with excursions reported within the 38-20 ka time interval (e.g. the Mono Lake excursion).
Magnetostratigraphy and its application on hominid and archaeological sites of East Africa
Magnetostratigraphy and its application on hominid and archaeological sites of East Africa.
Beryllium isotopes of sediments from the Portuguese margin, supplement to: Carcaillet, Julien; Bourlès, Didier L; Thouveny, Nicolas; Arnold, Maurice (2004): A high resolution authigenic 10Be/9Be record of geomagnetic moment variations over the last 300 ka from sedimentary cores of the Portuguese ...
A high resolution study of authigenic Be isotopes (10Be and 9Be) combined with continuous relativ... more A high resolution study of authigenic Be isotopes (10Be and 9Be) combined with continuous relative paleointensity records has been performed along the same marine sedimentary sequences from the Portuguese margin (NE Atlantic) covering the past 300 kyr in order to assess relationships between geomagnetic moment variations and 10Be production rate variations. A careful examination of the various ways of taking into account environmental disturbing effects on the authigenic 10Be concentration leads to the conclusion that the most reliable proxy of cosmonuclide production rates is presently the authigenic 10Be/9Be ratio. Eight intervals of significant authigenic 10Be/9Be enhancement evidence geomagnetic moment drops related to global paleomagnetic excursions, some being already admitted, others being proposed as new geomagnetic features. Since, unlike sedimentary magnetic remanence, the authigenic 10Be/9Be records dipole moment variations without significant acquisition delay, it provid...
(Figure 5) Stable oxygen isotope ratios on bulk carbonate of sediment core MD03-2698
(Figure 5) Calcium carbonate content of sediment core MD03-2698
(Table 1) Calculated ages of sediment core MD03-2698
Analytical results from sediment core MD03-2698
It is well established that orbital scale sea-level changes generated larger transport of sedimen... more It is well established that orbital scale sea-level changes generated larger transport of sediments into the deep-sea during the last glacial maximum than the Holocene. However, the response of sedimentary processes to abrupt millennial-scale climate variability is rather unknown. ...
(Table 1) AMS 14C measurements in sediment core MD03-2698
Quaternary Geochronology, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Quaternary Science Reviews, 2020
The evolution of temperatures during the Holocene is controversial, especially for the early Holo... more The evolution of temperatures during the Holocene is controversial, especially for the early Holocene. The occurrence of the Holocene Thermal Maximum (HTM) during the early Holocene has recently been reconsidered and seasonal biases have been suggested in the paleoclimatic proxies. High regional variability and a low number of reliable and continuous quantitative reconstructions compared with the oceanic realm further complicate study of the Holocene climate in the continental realm. We analyzed branched glycerol dialkyl glycerol tetraethers (brGDGTs), an organic paleothermometer, and palynological signals as part of a multiproxy analysis of the sedimentary record from Lake St Front, in the Massif Central (France). Identification of a shift in brGDGT sources through the Holocene required removing terrigenous influences from the temperature signal. BrGDGT-and pollen-inferred paleotemperature reconstructions (based on the Modern Analog Technique and the Weighted Averaging Partial Least Squares method) were compared. Both showed a thermal maximum during the early Holocene followed by a decrease of temperatures. We evaluated biases which could potentially influence the reconstructed signal. There was no evidence for a summer temperature bias either for brGDGT-derived temperatures or for pollen-derived temperatures. The Lake St Front data, in agreement with other regional records, confirm the occurrence of the HTM as a general warm period during the early Holocene followed by mid-Holocene cooling in Western Europe and suggest that seasonal biases are not the main explanation of the Holocene conundrum d the disagreement between model simulations and proxy-based temperature reconstructions for the northern hemisphere.
Organic Geochemistry, 2019
The distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) has been shown to co... more The distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) has been shown to correlate with mean annual air temperature and is increasingly used for paleoclimate reconstructions, in particular in lakes. Numerous studies have reported in situ production of brGDGTs in lakes. These brGDGTs have different distributions compared with those produced in soils and their mixing hampers paleoclimate reconstructions. Very few tools exist to determine brGDGT sources in the present and to trace their changes in the past linked with environmental changes of climatic or anthropogenic origin. While human activities are known to affect both soil and aquatic ecosystems, particularly bacterial communities, the specific impacts on brGDGT distributions are poorly investigated. High resolution analyses of brGDGTs were carried out on Holocene sediments and catchment soils of Lake St Front (Massif Central, France) in association with sedimentological, palynological, and geochemical analyses. Comparison of brGDGT distributions in sediments and soils revealed their mixed origin. For the first time, we tested the reliability of the RIIIa/RIIa ratio in lakes which indicated a gradual shift from aquatic to terrigenous brGDGT sources over the Holocene. This shift was supported by sedimentological and geochemical indices. Three events with a high proportion of terrigenous brGDGTs (6-5.5, 2.8-2.5, and 2-0.2 kyr cal BP) coincide with changes in vegetation in the catchment area, driven by climate and/or human activities. This suggests that vegetation modifications in the watershed impact brGDGT distributions and may thus bias brGDGT-based paleoclimatic reconstructions.
Earth and Planetary Science Letters, 2018
10 Be/ 9 Be ratio geomagnetic dipole moment minimum Matuyama-Brunhes transition (MBT) geomagnetic... more 10 Be/ 9 Be ratio geomagnetic dipole moment minimum Matuyama-Brunhes transition (MBT) geomagnetic polarity reversal marine isotope stage 19 atmospheric 10 Be production rates New high-resolution authigenic 10 Be/ 9 Be ratio (Be-ratio) records covering the last geomagnetic reversal, i.e. the Matuyama-Brunhes transition (MBT), have been obtained and set on a time scale using benthic δ 18 O (Cibicides wuellerstorfi) records. The geographic distribution of the four studied sites allows global comparison between the North Atlantic, Indian and Pacific Oceans. All Be-ratio records contain a twofold increase triggered by the geomagnetic dipole moment (GDM) collapse associated with the MBT. The stratigraphic position of the Be-ratio spike, relative to marine isotope stages, allows establishment of a robust astrochronological framework for the MBT, anchoring its age between 778 and 766 ka (average mid-peaks at 772 ka), which is consistent with all other available 10 Be-proxy records from marine, ice and loess archives. The global 10 Be atmospheric production doubling represents an increase of more than 300 atoms m −2 s −1 that is compatible with the increased magnitude of atmospheric 10 Be production obtained by simulations between the present GDM and a null-GDM. The minimum 10 Be-derived GDM average computed for the 776-771 ka interval is 1.7 ± 0.4 × 10 22 Am 2 , in agreement with model simulations and absolute paleointensities of transitional lava flows.
DeuxiΦme Partie Apports TerrigΦnes au cours des derniers 120 mille ans sur la Marge Sud-Ouest de la Basse Californie (Mexique)
Holocene environmental changes in northern Lebanon as inferred from a multiproxy study on lacustrine-palustrine sediment
International audienc
The multiproxy analysis of a lacustrine-palustrine sediment core from Lebanon reveals four climate cycles
International audienc
Earth and Planetary Science Letters, 2014
High-resolution records of beryllium (10 Be) production and relative paleointensity have been obt... more High-resolution records of beryllium (10 Be) production and relative paleointensity have been obtained across the Matuyama-Brunhes (M-B) reversal from the equatorial Indian Ocean (Maldives area). Both magnetic and geochemical analyses were performed from the same discrete samples to avoid any artificial depth offset. The authigenic 10 Be concentrations were normalized with respect to 9 Be in order to correct for potential environmental effects, while the relative paleointensity was derived from the remanent magnetization intensity after accounting for changes in magnetic concentration within the sediment. The relative paleointensity and the 10 Be/ 9 Be records are both characterized by large deviations, which culminate in the middle of the reversal. In contrast to most previous studies, and despite relative high deposition rate (4.7 cm/ka), we observed a perfect synchronism between the 10 Be/ 9 Be peak, the lowest value of relative paleointensity and the switch in direction, which indicates that bioturbation and post-depositional processes did not affect the magnetic record. This leaves no ambiguity for the stratigraphic position of the reversal located within Marine Isotopic Stage 19 as revealed by the planktonic δ 18 O record from the same core. The magnetic data depict a two-phase process with a precursory event preceding the rapid polarity switch, while only the second phase is present in the 10 Be record, similarly to other low latitude records from the Indonesian area. Using an orbitally-tuned age model, we obtain an age of 772 ka ± 5 ka for the middle of the transition, while the precursory event occurred almost 20 ka before. We believe that the bimodal distribution emerging from the compilations of the ages of the M-B reversal results from the succession of these two events. Microtektites from the Australasian impact were found at 0.6 m below the transition (790 ka ± 5 ka B.P.) and confirm that this large event occurred 12 ka prior to the polarity transition. The distribution of tektite abundance was used to deconvolve the 10 Be/ 9 Be signal. The results confirm that the beryllium changes are concentrated during the transitional period, thus likely in presence of a multipolar geomagnetic field (or in the vicinity of a geomagnetic pole) that favored the penetration of cosmic rays and consequently increased the 10 Be production. The absence of 10 Be during the precursor indicates that the present site and the Indonesian ones were far away from a geomagnetic pole and that interlatitudinal atmospheric mixing was limited. The geomagnetic pole positions above the Indonesian sites during the precursor would thus be incompatible with the corresponding inclined dipolar field during this period, and suggest the dominance of low-degree harmonics.
Earth and Planetary Science Letters, 2018
Quaternary Science Reviews, 2021
Reconstructions of the global production rate of the cosmogenic isotope 10 Be from sedimentary re... more Reconstructions of the global production rate of the cosmogenic isotope 10 Be from sedimentary records of authigenic 10 Be/ 9 Be ratios have been successfully used to obtain independent estimates of geomagnetic dipole moment variations caused by field excursions or reversals. In this study, we assess the reliability of 10 Be/ 9 Be as a proxy for the cosmogenic 10 Be production rate by evaluating two potential biasing sources represented by sediment composition and climatic modulation. For this purpose, we compare five high-resolution 10 Be/ 9 Be records of the Matuyama-Brunhes (M-B) field reversal from sediment cores of the Indian, West Pacific, and North Atlantic oceans. Significant increase of 10 Be/ 9 Be ratios at $774 ka is explained in terms of the dominant control of geomagnetic modulation during the M-B reversal. Results do not support the existence of a direct proportionality between measured sedimentary 10 Be/ 9 Be ratio and cosmogenic 10 Be production rate, as shown by 10 Be/ 9 Be records that offset relative to each other during and outside the M-B reversal. Residual differences between offset-corrected rescaled records do not appear to be related to an incomplete correction of variable sediment scavenging efficiencies by 9 Be normalization. Instead, these differences can be explained by a common climatic modulation model, assuming a linear relation between 10 Be/ 9 Be and the global 10 Be production rate with site-and time-dependent additive and multiplicative coefficients. These coefficients are linear functions of a single global climate proxy identified with the benthic d 18 O record. Additive coefficients are almost constant in time and can represent up to $60% of the average 10 Be/ 9 Be value during periods of stable field polarity. Multiplicative coefficients are also site-specific, with mean values representing the bulk scavenging efficiency of the site, and variations about this mean expressing a multiplicative climatic modulation of the 10 Be production rate. The amplitude of this modulation amounts to 10e15% of the maximum variations recorded during the M-B reversal and is sufficiently large to mask minor variations of the dipole moment during stable polarity periods. Reconstructions of the geomagnetic dipole intensity can benefit from the information about climatic modulation effects gained with our modelling approach. Best suited sites for magnetic field reconstructions should be characterized by minimal Be-recycling contributions from ancient 10 Be reservoirs and minimal climatic modulation, as far as it can be determined from relative comparisons with other records. These conditions are most likely encountered in open basins at sites (1) with < 2.8 km water depth, (2) > 200 km offshore, and (3) located underneath a large current system extending over regions with minimum terrigenous inputs. Scaling all records with respect to a chosen reference enables to produce 10 Be/ 9 Be stacks with reduced noise and short-term local environmental effects. Differences between stacks obtained in this manner highlight global climatic effects that need to be considered when generating calibrated reconstructions of the geomagnetic dipole moment.
Uploads
Papers by Nicolas Thouveny