Maurice Arnold

Bio: Maurice Arnold is an academic researcher from Aix-Marseille University. The author has contributed to research in topics: Younger Dryas & Deglaciation. The author has an hindex of 59, co-authored 141 publications receiving 11774 citations. Previous affiliations of Maurice Arnold include Centre national de la recherche scientifique & Aster.

Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge

Abstract: THE timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the Earth's surface2,3. Moreover, the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans, which probably disturbed the ocean's thermohaline circulation and, hence, global climate4–7. Sea-level increases bear witness to the melting of continental ice sheets, but only two such records—from Barbados8,9 and New Guinea10,11 corals—have been accurately dated. But these corals overlie active subduction zones, where tectonic movements are large and often discontinuous (especially in New Guinea), so the apparent sea-level records may be contaminated by a complex tectonic component. Here we date fossil corals from Tahiti, which is far from plate boundaries (and thus is likely to be tectonically relatively stable) and remote from the locations of large former ice sheets. The resulting record indicates a large sea-level jump shortly before 13,800 calendar years BP, which corresponds to meltwater pulse 1A in the Barbados coral records8,9. The timing of this event is more accurately constrained in the Tahiti record, revealing that the meltwater pulse coincides with a short and intense climate cooling event12–15 that followed the initiation of the Bolling–Allerod warm period12–16, but preceded the Younger Dryas cold event by about 1,000 years.

A 13,000-year climate record from western tibet

Abstract: ALTHOUGH the Tibetan plateau is important in influencing the atmospheric circulation of the Northern Hemisphere1–3, there are only a few continuous palaeoclimate records available, and these are limited to the plateau's northeastern margin4–6. Here we present a 13,000-yr record from Sumxi Co (western Tibet), constructed from both lake-core and shoreline studies, which shows that conditions in the early–middle Holocene were warmer and wetter than at present. These results confirm model predictions of an intensified monsoon over the region at ∼9,000 yr BP, owing to an orbitally induced increase in summer insolation7,8. We also find evidence for warm, humid pulses at ∼12,500 and ∼10,000 yr BP, in phase with the steps of the last deglaciation, and for a return to cold, dry conditions at ∼11-10,000 yr BP, none of which can be explained by orbital variations. The existence of the cold episode confirms that the cooling associated with the Younger Dry as event occurred in continental China6,9, and provides further evidence of the global nature of this event10

Century-scale events in monsoonal climate over the past 24,000 years

Abstract: BOTH the marine sediment record and numerical modelling of the atmospheric summer circulation over the northern Indian Ocean and southeast Asia have shown that the monsoonal climate exhibits a direct but nonlinear response to the intensity of solar insolation during summer, with a time lag of several thousand years1,2. Here we present evidence from a high-resolution record of oxygen isotopes and carbonate spanning the past 24,000 calendar years that the response of the southwest monsoon over the Arabian Sea to long-term, gradual insolation changes occurred in several distinct events of less than 300 years duration, at 14,300, 13,500, 13,060, 9,900, 8,800 and 7,30014C yr BP. Thus, during this transitional period from glacial to post-glacial conditions the slow solar forcing seems to have induced very rapid changes in local climate. We speculate that the rapid response may be related to albedo changes in Asia.

230Th-234U and 14C Ages Obtained by Mass Spectrometry on Corals

Abstract: In 1988, Fairbanks conducted a drilling expedition off the south coast of Barbados to recover submerged corals contemporaneous with the last deglaciation. Core recovery was excellent and >30 different samples were dated by conventional β-counting techniques (Fairbanks 1989). At about the same time, we developed, at Lamont, the thermal ionization mass spectrometry (TIMS) technique to obtain precise U-Th ages (Edwards 1988), and to compare them with the 14C estimates measured on the same samples. A surprising result was that the discrepancy between 14C and U-Th ages increased through time to ca. 3000–3500 yr at ca. 15,000 14C BP (Bard et al. 1990a). Because the three youngest samples yielded U-Th ages in agreement with their calibrated 14C ages, we concluded initially that the TIMS U-Th determinations were not only precise, but also accurate, and that the 14C vs. U-Th data set could be used for a first-order 14C calibration.

Radiocarbon Calibration by Means of Mass Spectrometric 230Th/234U and 14C Ages of Corals: An Updated Database Including Samples from Barbados, Mururoa and Tahiti

Abstract: As first shown by Bard et al. (1990a), high-precision 230Th-234U ages can be used successfully to calibrate the radiocarbon time scale beyond the high-precision tree-ring calibration that now reaches 11,900 cal BP (Kromer and Spurk 1998). Using mass spectrometric techniques, we measured 14C and 230Th ages on new samples collected from boreholes drilled off the islands of Tahiti and Mururoa (French Polynesia) in order to complement the database previously obtained on Barbados corals (Bard et al. 1990a, 1993). METHODS New 230Th/234U ages for Tahiti and Mururoa samples (Table 1) were measured with a VG-54-30 thermal ionization mass spectrometer (TIMS) fitted with an ion-counting Daly detector, at CEREGE (Aix-en-Provence). The chemical separations were similar to those previously described (Bard et al. 1990b). The 26 precision of the 230Th ages ranges from 30 to 60 yr, for ages between 8000 and 14,000 230Th yr BP.4 This represents an improvement by a factor of 2 to 3 over the performance obtained on Barbados corals by single collection and analog Daly detector on an MM30 mass spectrometer (Table 1; Bard et al. 1990a,b). The precision of the ages was checked by measuring numerous replicates (Bard et al. 1996). In particular, we performed five analyses of different pieces of the same coral specimen (sample P7-7: 10,995 ± 40, 11,005 ± 30, 11,025 ± 30, 10,995 ±30 and 10,995 ± 30 230Th yr BP; ages are rounded to the nearest 5 yr). The five 230Th/234U ages agree with each other within the 26 uncertainties, with an overall 2c uncertainty on the mean of 12 yr and a maximum difference between replicates of ca. 30 yr. Following Ludwig et al. (1992) and Stirling et al. (1995), the 229Th/ 33U ratio of our mixed spike was calibrated against the uraninite standard HU1 assumed to be at exact secular equilibrium. This calibration was shown to be accurate within 5% by means of gravimetric U and Th standards. This agreement is satisfactory if one takes into account the overall uncertainty on the half-lives of 234U and 230Th (2%o and 8%o, respectively; see Ludwig et al. 1992). Th samples are loaded with colloidal graphite on single-zone refined Re filaments and U samples on Re-Ta triple filaments. 234U/238U ratios are measured in dynamic multicollection mode: 233U, 234U and 235U ion beams are measured with the Daly ion counting detector, whereas 235U and 238U ion currents are measured with Faraday cups. Correction for isotopic fractionation is performed by normalizing the measured 238U/235U atomic ratio to the natural value (137.88). Faraday/Daly gain is monitored with 235U signals during each measurement block in order to correct for possible shifts of the gain. The external precision on individual values of b234U; (= [initial234U /238U-1 ] x 1000) is on the order of 2% (at 2a), as shown by repeated measurements of standards. The accuracy has been checked by ages expressed here as "BP" are relative to a fixed present of 1950.

IntCal13 and Marine13 radiocarbon age calibration curves 0-50,000 years cal BP

Abstract: Additional co-authors: TJ Heaton, AG Hogg, KA Hughen, KF Kaiser, B Kromer, SW Manning, RW Reimer, DA Richards, JR Southon, S Talamo, CSM Turney, J van der Plicht, CE Weyhenmeyer

Extended 14C Data Base and Revised Calib 3.0 14C Age Calibration Program

Abstract: The age calibration program, CALIB (Stuiver & Reimer 1986), first made available in 1986 and subsequently modified in 1987 (revision 2.0 and 2.1), has been amended anew. The 1993 program (revision 3.0) incorporates further refinements and a new calibration data set covering nearly 22,000 cal yr (≈18,400 14C yr). The new data, and corrections to the previously used data set, derive from a 6-yr (1986–1992) time-scale calibration effort of several laboratories.

A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation

Abstract: Coral reefs drilled offshore of Barbados provide the first continuous and detailed record of sea level change during the last deglaciation. The sea level was 121 ± 5 metres below present level during the last glacial maximum. The deglacial sea level rise was not monotonic; rather, it was marked by two intervals of rapid rise. Varying rates of melt-water discharge to the North Atlantic surface ocean dramatically affected North Atlantic deep-water production and oceanic oxygen isotope chemistry. A global oxygen isotope record for ocean water has been calculated from the Barbados sea level curve, allowing separation of the ice volume component common to all oxygen isotope records measured in deep-sea cores.

INTCAL98 Radiocarbon Age Calibration, 24,000-0 cal BP

Abstract: The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000-0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14C age-cal age information, produced by many laboratories, is converted to 14C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured 14C ages and the errors therein, regional 14C age differences, tree-coral 14C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year 14C results. Changes in oceanic deepwater circulation, especially for the 16,000-11,000 cal BP interval, are reflected in the Δ 14C values of INTCAL98.

IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP

Abstract: A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).