Publications by authors named "Edouard Bard"

18 Publications

  • Page 1 of 1

Extended dilation of the radiocarbon time scale between 40,000 and 48,000 y BP and the overlap between Neanderthals and .

Proc Natl Acad Sci U S A 2020 09 17;117(35):21005-21007. Epub 2020 Aug 17.

The CHRONO Centre for Climate, the Environment and Chronology, School of Natural and Built Environment, Queen's University Belfast, BT7 1NN Belfast, United Kingdom.

The new radiocarbon calibration curve (IntCal20) allows us to calculate the gradient of the relationship between C age and calendar age over the past 55 millennia before the present (55 ka BP). The new gradient curve exhibits a prolonged and prominent maximum between 48 and 40 ka BP during which the radiocarbon clock runs almost twice as fast as it should. This radiocarbon time dilation is due to the increase in the atmospheric C/C ratio caused by the C production rise linked to the transition into the Laschamp geomagnetic excursion centered around 41 ka BP. The major maximum in the gradient from 48 to 40 ka BP is a new feature of the IntCal20 calibration curve, with far-reaching impacts for scientific communities, such as prehistory and paleoclimatology, relying on accurate ages in this time range. To illustrate, we consider the duration of the overlap between Neanderthals and in Eurasia.
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http://dx.doi.org/10.1073/pnas.2012307117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7474600PMC
September 2020

Initial Upper Palaeolithic Homo sapiens from Bacho Kiro Cave, Bulgaria.

Nature 2020 05 11;581(7808):299-302. Epub 2020 May 11.

Archaeology Department, New Bulgarian University, Sofia, Bulgaria.

The Middle to Upper Palaeolithic transition in Europe witnessed the replacement and partial absorption of local Neanderthal populations by Homo sapiens populations of African origin. However, this process probably varied across regions and its details remain largely unknown. In particular, the duration of chronological overlap between the two groups is much debated, as are the implications of this overlap for the nature of the biological and cultural interactions between Neanderthals and H. sapiens. Here we report the discovery and direct dating of human remains found in association with Initial Upper Palaeolithic artefacts, from excavations at Bacho Kiro Cave (Bulgaria). Morphological analysis of a tooth and mitochondrial DNA from several hominin bone fragments, identified through proteomic screening, assign these finds to H. sapiens and link the expansion of Initial Upper Palaeolithic technologies with the spread of H. sapiens into the mid-latitudes of Eurasia before 45 thousand years ago. The excavations yielded a wealth of bone artefacts, including pendants manufactured from cave bear teeth that are reminiscent of those later produced by the last Neanderthals of western Europe. These finds are consistent with models based on the arrival of multiple waves of H. sapiens into Europe coming into contact with declining Neanderthal populations.
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http://dx.doi.org/10.1038/s41586-020-2259-zDOI Listing
May 2020

A C chronology for the Middle to Upper Palaeolithic transition at Bacho Kiro Cave, Bulgaria.

Nat Ecol Evol 2020 06 11;4(6):794-801. Epub 2020 May 11.

Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.

The stratigraphy at Bacho Kiro Cave, Bulgaria, spans the Middle to Upper Palaeolithic transition, including an Initial Upper Palaeolithic (IUP) assemblage argued to represent the earliest arrival of Upper Palaeolithic Homo sapiens in Europe. We applied the latest techniques in C dating to an extensive dataset of newly excavated animal and human bones to produce a robust, high-precision radiocarbon chronology for the site. At the base of the stratigraphy, the Middle Palaeolithic (MP) occupation dates to >51,000 yr BP. A chronological gap of over 3,000 years separates the MP occupation from the occupation of the cave by H. sapiens, which extends to 34,000 cal BP. The extensive IUP assemblage, now associated with directly dated H. sapiens fossils at this site, securely dates to 45,820-43,650 cal BP (95.4% probability), probably beginning from 46,940 cal BP (95.4% probability). The results provide chronological context for the early occupation of Europe by Upper Palaeolithic H. sapiens.
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http://dx.doi.org/10.1038/s41559-020-1136-3DOI Listing
June 2020

Shut down of the South American summer monsoon during the penultimate glacial.

Sci Rep 2020 04 15;10(1):6275. Epub 2020 Apr 15.

CEREGE, Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, 13545, Aix-en-Provence, France.

We analysed changes in mean annual air temperature (MAAT), vegetation and biomass burning on a long and continuous lake-peat sediment record from the Colônia basin, southeastern Brazil, examining the responses of a wet tropical rainforest over the last 180 ka. Stronger southern atmospheric circulation up to the latitude of Colônia was found for the penultimate glacial with lower temperatures than during the last glacial, while strengthening of the South American summer monsoon (SASM) circulation started during the last interglacial and progressively enhanced a longer wet summer season from 95 ka until the present. Past MAAT variations and fire history were possibly modulated by eccentricity, although with signatures which differ in average and in amplitude between the last 180 ka. Vegetation responses were driven by the interplay between the SASM and southern circulation linked to Antarctic ice volume, inferred by the presence of a cool mixed evergreen forest from 180 to 45 ka progressively replaced by a rainforest. We report cooler temperatures during the marine isotope stage 3 (MIS 3: 57-29 ka) than during the Last Glacial Maximum (LGM: 23-19 ka). Our findings show that tropical forest dynamics display different patterns than mid-latitude during the last 180 ka.
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http://dx.doi.org/10.1038/s41598-020-62888-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7160121PMC
April 2020

Liquid chromatographic isolation of individual carbohydrates from environmental matrices for stable carbon analysis and radiocarbon dating.

Anal Chim Acta 2019 Aug 18;1067:137-146. Epub 2019 Mar 18.

Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, France.

Carbohydrates are among the most abundant organic molecules in both aquatic and terrestrial ecosystems; however, very few studies have addressed their isotopic signature using compound-specific isotope analysis, which provides additional information on their origin (δC) and fate (ΔC). In this study, semi-preparative liquid chromatography with refractive index detection (HPLC-RI) was employed to produce pure carbohydrate targets for subsequent offline δC and ΔC isotopic analysis. δC analysis was performed by elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) whereas ΔC analysis was performed by an innovative measurement procedure based on the direct combustion of the isolated fractions using an elemental analyzer coupled to the gas source of a mini carbon dating system (AixMICADAS). In general, four successive purifications with Na, Ca, Pb, and Ca cation-exchange columns were sufficient to produce pure carbohydrates. These carbohydrates were subsequently identified using mass spectrometry by comparing their mass spectra with those of authentic standards. The applicability of the proposed method was tested on two different environmental samples comprising marine particulate organic matter (POM) and total suspended atmospheric particles (TSP). The obtained results revealed that for the marine POM sample, the δC values of the individual carbohydrates ranged from -18.5 to -16.8‰, except for levoglucosan and mannosan, which presented values of -27.2 and -26.2‰, respectively. For the TSP sample, the δC values ranged from -26.4 to -25.0‰. The galactose and glucose ΔC values were 19 and 43‰, respectively, for the POM sample. On the other hand, the levoglucosan radiocarbon value was 33‰ for the TSP sample. These results suggest that these carbohydrates exhibit a modern age in both of these samples. Radiocarbon HPLC collection window blanks, measured after the addition of phthalic acid (C free blank), ranged from -988 to -986‰ for the abovementioned compounds, indicating a very small background isotopic influence from the whole purification procedure. Overall, the proposed method does not require derivatization steps, produces extremely low blanks, and may be applied to different types of environmental samples.
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http://dx.doi.org/10.1016/j.aca.2019.03.028DOI Listing
August 2019

Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. (∼660 BC).

Proc Natl Acad Sci U S A 2019 03 11;116(13):5961-5966. Epub 2019 Mar 11.

Department of Geology-Quaternary Sciences, Lund University, 22362 Lund, Sweden;

Recently, it has been confirmed that extreme solar proton events can lead to significantly increased atmospheric production rates of cosmogenic radionuclides. Evidence of such events is recorded in annually resolved natural archives, such as tree rings [carbon-14 (C)] and ice cores [beryllium-10 (Be), chlorine-36 (Cl)]. Here, we show evidence for an extreme solar event around 2,610 years B.P. (∼660 BC) based on high-resolution Be data from two Greenland ice cores. Our conclusions are supported by modeled C production rates for the same period. Using existing Cl ice core data in conjunction with Be, we further show that this solar event was characterized by a very hard energy spectrum. These results indicate that the 2,610-years B.P. event was an order of magnitude stronger than any solar event recorded during the instrumental period and comparable with the solar proton event of AD 774/775, the largest solar event known to date. The results illustrate the importance of multiple ice core radionuclide measurements for the reliable identification of short-term production rate increases and the assessment of their origins.
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http://dx.doi.org/10.1073/pnas.1815725116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6442557PMC
March 2019

Permafrost thawing as a possible source of abrupt carbon release at the onset of the Bølling/Allerød.

Nat Commun 2014 Nov 20;5:5520. Epub 2014 Nov 20.

CEREGE, Aix Marseille University, CNRS, IRD, College de France, B.P. 80 Technopole de l'Arbois, 13545 Aix-en-Provence, France.

One of the most abrupt and yet unexplained past rises in atmospheric CO2 (>10 p.p.m.v. in two centuries) occurred in quasi-synchrony with abrupt northern hemispheric warming into the Bølling/Allerød, ~14,600 years ago. Here we use a U/Th-dated record of atmospheric Δ(14)C from Tahiti corals to provide an independent and precise age control for this CO2 rise. We also use model simulations to show that the release of old (nearly (14)C-free) carbon can explain these changes in CO2 and Δ(14)C. The Δ(14)C record provides an independent constraint on the amount of carbon released (~125 Pg C). We suggest, in line with observations of atmospheric CH4 and terrigenous biomarkers, that thawing permafrost in high northern latitudes could have been the source of carbon, possibly with contribution from flooding of the Siberian continental shelf during meltwater pulse 1A. Our findings highlight the potential of the permafrost carbon reservoir to modulate abrupt climate changes via greenhouse-gas feedbacks.
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http://dx.doi.org/10.1038/ncomms6520DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4263146PMC
November 2014

Climate change. Out of the African Humid Period.

Authors:
Edouard Bard

Science 2013 Nov;342(6160):808-9

Collège de France and CEREGE (Aix-Marseille University, CNRS, IRD, CdF), Aix-en-Provence F-13545, France.

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http://dx.doi.org/10.1126/science.1246519DOI Listing
November 2013

Abrupt drainage cycles of the Fennoscandian Ice Sheet.

Proc Natl Acad Sci U S A 2013 Apr 8;110(17):6682-7. Epub 2013 Apr 8.

Aix Marseille Université, Centre National de la Recherche Scientifique, Institut de Recherche pour le Développement, Collège de France, 13545 Aix-en-Provence Cedex 04, France.

Continental ice sheets are a key component of the Earth's climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate-lake-FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas.
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http://dx.doi.org/10.1073/pnas.1214676110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637780PMC
April 2013

Pronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1.

Nat Commun 2012 Jul 24;3:965. Epub 2012 Jul 24.

MARUM-Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany.

The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation. This interval between ~18,000 and 14,600 years ago, known as Heinrich Stadial 1, was accompanied by a disruption of global climate and has been suggested as a key factor for the termination. However, the response of interannual climate variability in the tropical Pacific (El Niño-Southern Oscillation) to Heinrich Stadial 1 is poorly understood. Here we use Sr/Ca in a fossil Tahiti coral to reconstruct tropical South Pacific sea surface temperature around 15,000 years ago at monthly resolution. Unlike today, interannual South Pacific sea surface temperature variability at typical El Niño-Southern Oscillation periods was pronounced at Tahiti. Our results indicate that the El Niño-Southern Oscillation was active during Heinrich Stadial 1, consistent with climate model simulations of enhanced El Niño-Southern Oscillation variability at that time. Furthermore, a greater El Niño-Southern Oscillation influence in the South Pacific during Heinrich Stadial 1 is suggested, resulting from a southward expansion or shift of El Niño-Southern Oscillation sea surface temperature anomalies.
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http://dx.doi.org/10.1038/ncomms1973DOI Listing
July 2012

Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation.

Nature 2012 Apr 4;484(7392):49-54. Epub 2012 Apr 4.

Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.

The covariation of carbon dioxide (CO(2)) concentration and temperature in Antarctic ice-core records suggests a close link between CO(2) and climate during the Pleistocene ice ages. The role and relative importance of CO(2) in producing these climate changes remains unclear, however, in part because the ice-core deuterium record reflects local rather than global temperature. Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO(2) during the last (that is, the most recent) deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO(2) concentrations is an explanation for much of the temperature change at the end of the most recent ice age.
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http://dx.doi.org/10.1038/nature10915DOI Listing
April 2012

Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago.

Nature 2012 Mar 28;483(7391):559-64. Epub 2012 Mar 28.

CEREGE, UMR Aix-Marseille Université - CNRS - IRD - College de France, Technopole de l'Arbois, BP 80, 13545 Aix-en-Provence Cedex 4, France.

Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the Bølling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A.
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http://dx.doi.org/10.1038/nature10902DOI Listing
March 2012

Deglacial meltwater pulse 1B and Younger Dryas sea levels revisited with boreholes at Tahiti.

Science 2010 Mar 14;327(5970):1235-7. Epub 2010 Jan 14.

Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement (CEREGE), UMR 6635 CNRS, University Aix-Marseille, Institut de Recherche pour le Développement, Collège de France, Europôle de l'Arbois, BP 80, F-13545 Aix-en-Provence Cedex 4, France.

Reconstructing sea-level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets. The resolution of the few sea-level records covering the critical time interval between 14,000 and 9,000 calendar years before the present is still insufficient to draw conclusions about sea-level changes associated with the Younger Dryas cold event and the meltwater pulse 1B (MWP-1B). We used the uranium-thorium method to date shallow-living corals from three new cores drilled onshore in the Tahiti barrier reef. No significant discontinuity can be detected in the sea-level rise during the MWP-1B period. The new Tahiti sea-level record shows that the sea-level rise slowed down during the Younger Dryas before accelerating again during the Holocene.
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http://dx.doi.org/10.1126/science.1180557DOI Listing
March 2010

Migration of the subtropical front as a modulator of glacial climate.

Nature 2009 Jul;460(7253):380-3

CEREGE (UMR 6635), Collège de France, University Paul-Cézanne Aix-Marseille, CNRS, IRD, Europole de l'Arbois BP 80, 13545 Aix-en-Provence Cedex 4, France.

Ice cores extracted from the Antarctic ice sheet suggest that glacial conditions, and the relationship between isotopically derived temperatures and atmospheric PCO(2) have been constant over the last 800,000 years of the Late Pleistocene epoch. But independent lines of evidence, such as the extent of Northern Hemisphere ice sheets, sea level and other temperature records, point towards a fluctuating severity of glacial periods, particularly during the more extreme glacial stadials centred around 340,000 and 420,000 years ago (marine isotope stages 10 and 12). Previously unidentified mechanisms therefore appear to have mediated the relationship between insolation, CO(2) and climate. Here we test whether northward migration of the subtropical front (STF) off the southeastern coast of South Africa acts as a gatekeeper for the Agulhas current, which controls the transport of heat and salt from the Indo-Pacific Ocean to the Atlantic Ocean. Using a new 800,000-year record of sea surface temperature and ocean productivity from ocean sediment core MD962077, we demonstrate that during cold stadials (particularly marine isotope stages 10 and 12), productivity peaked and sea surface temperature was up to 6 degrees C cooler than modern temperatures. This suggests that during these cooler stadials, the STF moved northward by up to 7 degrees latitude, nearly shutting off the Agulhas current. Our results, combined with faunal assemblages from the south Atlantic show that variable northwards migration of the Southern Hemisphere STF can modulate the severity of each glacial period by altering the strength of the Agulhas current carrying heat and salt to the Atlantic meridional overturning circulation. We show hence that the degree of northwards migration of the STF can partially decouple global climate from atmospheric partial pressure of carbon dioxide, P CO(2), and help to resolve the long-standing puzzle of differing glacial amplitudes within a consistent range of atmospheric PCO(2).
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http://dx.doi.org/10.1038/nature08189DOI Listing
July 2009

Penultimate deglacial sea-level timing from uranium/thorium dating of Tahitian corals.

Science 2009 May 23;324(5931):1186-9. Epub 2009 Apr 23.

Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK.

The timing of sea-level change provides important constraints on the mechanisms driving Earth's climate between glacial and interglacial states. Fossil corals constrain the timing of past sea level by their suitability for dating and their growth position close to sea level. The coral-derived age for the last deglaciation is consistent with climate change forced by Northern Hemisphere summer insolation (NHI), but the timing of the penultimate deglaciation is more controversial. We found, by means of uranium/thorium dating of fossil corals, that sea level during the penultimate deglaciation had risen to ~85 meters below the present sea level by 137,000 years ago, and that it fluctuated on a millennial time scale during deglaciation. This indicates that the penultimate deglaciation occurred earlier with respect to NHI than the last deglacial, beginning when NHI was at a minimum.
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http://dx.doi.org/10.1126/science.1168754DOI Listing
May 2009

Moisture transport across Central America as a positive feedback on abrupt climatic changes.

Nature 2007 Feb;445(7130):908-11

CEREGE, UMR6635, CNRS Université Paul Cézanne Aix-Marseille III, Collège de France, Europôle de l'Arbois, BP 80, 13545 Aix-en-Provence Cedex 04, France.

Moisture transport from the Atlantic to the Pacific ocean across Central America leads to relatively high salinities in the North Atlantic Ocean and contributes to the formation of North Atlantic Deep Water. This deep water formation varied strongly between Dansgaard/Oeschger interstadials and Heinrich events-millennial-scale abrupt warm and cold events, respectively, during the last glacial period. Increases in the moisture transport across Central America have been proposed to coincide with northerly shifts of the Intertropical Convergence Zone and with Dansgaard/Oeschger interstadials, with opposite changes for Heinrich events. Here we reconstruct sea surface salinities in the eastern equatorial Pacific Ocean over the past 90,000 years by comparing palaeotemperature estimates from alkenones and Mg/Ca ratios with foraminiferal oxygen isotope ratios that vary with both temperature and salinity. We detect millennial-scale fluctuations of sea surface salinities in the eastern equatorial Pacific Ocean of up to two to four practical salinity units. High salinities are associated with the southward migration of the tropical Atlantic Intertropical Convergence Zone, coinciding with Heinrich events and with Greenland stadials. The amplitudes of these salinity variations are significantly larger on the Pacific side of the Panama isthmus, as inferred from a comparison of our data with a palaeoclimate record from the Caribbean basin. We conclude that millennial-scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes, modulating the North Atlantic freshwater budget and hence North Atlantic Deep Water formation.
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http://dx.doi.org/10.1038/nature05578DOI Listing
February 2007

Early reactivation of European rivers during the last deglaciation.

Science 2006 Sep;313(5793):1623-5

CEREGE, Collège de France, UMR 6635, CNRS Université Aix-Marseille III, Europole de l'Arbois, BP 80, 13545 Aix-en-Provence, France.

During the Last Glacial Maximum, the sea-level lowstand combined with the large extent of the Fennoscandian and British ice sheets led to the funneling of European continental runoff, resulting in the largest river system that ever drained the European continent. Here, we show an abrupt and early reactivation of the European hydrological cycle at the onset of the last deglaciation, leading to intense discharge of the Channel River into the Bay of Biscay. This freshwater influx, probably combined with inputs from proglacial or ice-dammed lakes, dramatically affected the hydrology of the region, both on land and in the ocean.
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http://dx.doi.org/10.1126/science.1130511DOI Listing
September 2006

Paleoclimate. A better radiocarbon clock.

Science 2004 Jan;303(5655):178-9

CEREGE, UMR 6635 and Collège de France, 13545 Aix-en-Provence, France.

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http://dx.doi.org/10.1126/science.1091964DOI Listing
January 2004