Age of the Laschamp paleomagnetic excursion revisited

Gillot, P. Y.; Labeyrie, J.; Làj, C.; Valladas, G.; Guérin, Gilles; Poupeau, Gérard; Delibrias, G.

doi:10.1016/0012-821x(79)90053-0

Cited by 124 publications

(50 citation statements)

References 9 publications

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“…To account for past changes in 14 C production, these ages were converted to calendar ages assuming 400 years of reservoir age and applying the INTCAL98 calibration curve for ages up to 24 ka (11) and a polynomial calibration based on coupled 14 C͞ U/Th ages in corals for ages Ͼ24 ka (12). The Laschamp excursion (1,050 cm) is well marked in the magnetic record (C. L. Blanchet, N. Thouveny, and T.d.G.-T., unpublished results) and provides a chronological datum in marine isotope stage (MIS) 3 at 40 ka (13). The similarity of MD97-2134 paleointensity record with paleomagnetic reference stacks indicates that no hiatus interrupts the sediment record during the last 60 ky.…”

Section: Methodsmentioning

confidence: 91%

Evidence for large methane releases to the atmosphere from deep-sea gas-hydrate dissociation during the last glacial episode

Garidel‐Thoron

Beaufort

Bassinot

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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Past atmospheric methane-concentration oscillations recorded in polar ice cores vary together with rapid global climatic changes during the last glacial episode. In the ''clathrate gun hypothesis,'' massive releases of deep-sea methane from marine gas-hydrate dissociation led to these well known, global, abrupt warmings in the past. If evidence for such releases in the water column exists, however, the mechanism and eventual transfer to the atmosphere has not yet been documented clearly. Here we describe a highresolution marine-sediment record of stable carbon isotopic changes from the Papua Gulf, off Papua New Guinea, which exhibits two extremely depleted excursions (down to ؊9‰) at Ϸ39,000 and Ϸ55,000 years. Morphological, isotopic, and trace metal evidence dismisses authigenic calcite as the main source of depleted carbon. Massive methane release associated with deepsea gas-hydrate dissociation is the most likely cause for such large depletions of ␦ 13 C. The absence of a ␦ 13 C gradient in the water column during these events implies that the methane rose through the entire water column, reaching the sea-air interface and thus the atmosphere. Foraminiferal ␦ 18 O composition suggests that the rise of the methane in the water column created an upwelling flow. These inferred emission events suggest that during the last glacial episode, this process was likely widespread, including tropical regions. Thus, the release of methane from the ocean floor into the atmosphere cannot be dismissed as a strong positive feedback in climate dynamics processes.

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Section: Methodsmentioning

confidence: 91%

Evidence for large methane releases to the atmosphere from deep-sea gas-hydrate dissociation during the last glacial episode

Garidel‐Thoron

Beaufort

Bassinot

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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“…The basic chronology of core 25-GC1 is based on marker horizons such as the Laschamp geomagnetic excursion at 40.70 ± 0.95 ka BP (Bonhommet and Babkine, 1967;Gillot et al, 1979;Guillou et al, 2004;Plenier et al 2007;Nowaczyk et al, 2012), the Campanian Ignimbrite tephra at 39.28 ± 0.11 ka (DeVito et al, 2001;Pyle et al, 2006), the Korudagıtephra at ∼ 20 ka ± 6 ka (Kuzucuoglu et al, 1998), the Santorini tephra at ∼ 1627-1600 yr BC (Guichard et al, 1993;Friedrich et al, 2006), (Fig. 2).…”

Section: Chronological Frameworkmentioning

confidence: 99%

“…Shumilovskikh et al, 2012) or rather presence/absence of distinct species. Freshwater/brackish dinocysts include Pyxidinopsis psilata, Spiniferites cruciformis and Caspidinium rugosum, and marine dinocysts include Lingulodinium machaerophorum, Operculodinium centrocarpum, Tuberculodinium (Guichard et al, 1993;Friedrich et al, 2006), Korudagı tephra (Kuzucuoglu et al, 1998), Campanian Ignimbrite tephra (De Vivo et al, 2001;Pyle et al, 2006), Laschamp Event (Bonhommet and Babkine, 1967;Gillot et al, 1979;Guillou et al, 2004;Plenier et al, 2007;Nowaczyk et al, 2012), PJA (paleointensity based on anhysteretic remanent magnetization) -relative paleointensity of 25-GC1 tuned to MD95-2024 (Stoner et al, 2000), 25-GC1 proxy tuning to North Greenland Ice core Project (NGRIP) δ 18 O record (Svensson et al, 2008) and to the Black Sea sediment records GeoB-7622 and MD04-2788 .…”

Section: Palynological Investigationsmentioning

confidence: 99%

Orbital- and millennial-scale environmental changes between 64 and 20 ka BP recorded in Black Sea sediments

Shumilovskikh¹,

Fleitmann

Nowaczyk

et al. 2014

Clim. Past

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Abstract. High-resolution pollen and dinoflagellate cyst records from sediment core M72/5-25-GC1 were used to reconstruct vegetation dynamics in northern Anatolia and surface conditions of the Black Sea between 64 and 20 ka BP. During this period, the dominance of Artemisia in the pollen record indicates a steppe landscape and arid climate conditions. However, the concomitant presence of temperate arboreal pollen suggests the existence of glacial refugia in northern Anatolia. Long-term glacial vegetation dynamics reveal two major arid phases ∼ 64-55 and 40-32 ka BP, and two major humid phases ∼ 54-45 and 28-20 ka BP, correlating with higher and lower summer insolation, respectively. Dansgaard-Oeschger (D-O) cycles are clearly indicated by the 25-GC1 pollen record. Greenland interstadials are characterized by a marked increase in temperate tree pollen, indicating a spread of forests due to warm/wet conditions in northern Anatolia, whereas Greenland stadials reveal cold and arid conditions as indicated by spread of xerophytic biomes. There is evidence for a phase lag of ∼ 500 to 1500 yr between initial warming and forest expansion, possibly due to successive changes in atmospheric circulation in the North Atlantic sector. The dominance of Pyxidinopsis psilata and Spiniferites cruciformis in the dinocyst record indicates brackish Black Sea conditions during the entire glacial period. The decrease of marine indicators (marine dinocysts, acritarchs) at ∼ 54 ka BP and increase of freshwater algae (Pediastrum, Botryococcus) from 32 to 25 ka BP reveals freshening of the Black Sea surface water. This freshening is possibly related to humid phases in the region, to connection between Caspian Sea and Black Sea, to seasonal freshening by floating ice, and/or to closer position of river mouths due to low sea level. In the southern Black Sea, Greenland interstadials are clearly indicated by high dinocyst concentrations and calcium carbonate content, as a result of an increase in primary productivity. Heinrich events show a similar impact on the environment in the northern Anatolia/Black Sea region as Greenland stadials.

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“…Two series of experiments were made, firstly by a conventional method using a spike of 38Ar, and secondly by an amplitude method which does not involve 38Ar spikes but which determines the Ar content solely by the peak height assuming constant sensitivity of the machine. The latter method was first described by Gillot et al (1979), and is widely used for dating ultra young volcanic rocks in which the content of radiogenic 40Ar is extremely low (Nagao et al, 1991). One of the merits of this method is that the 38Ar/36Ar ratio of trapped Ar is obtained and we can use it to correct the effect of mass dependent fractionation of Ar which has often been recognized in volcanic rocks (Kaneoka, 1980).…”

Section: Geology and K-ar Datingmentioning

confidence: 99%

K-Ar Ages and Paleosecular Variation of Direction and Intensity from Quaternary Lava Sequences in the Ruapehu Volcano, New Zealand.

Tanaka

Kawamura

Nagao

et al. 1997

J. geomagn. geoelec

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Andesite lava sequences of the Quaternary Ruapehu Volcano, New Zealand were studied to obtain paleosecular variations, both direction and intensity.K-Ar dating was performed on 7 lavas of the younger Whakapapa Formation and 22 lavas of the older Te Herenga Formation. Initial experiments by the isotope dilution method using an 38Ar spike were unsuccessful on the younger lavas, while an amplitude method in which the abundance of Ar is estimated from a peak height of mass spectrum gave consistent results of 32 f 12 ka after the correction of the Ar isotopic ratios for mass dependent fractionation. The latter method also gave a more accurate result of 229 ± 35 ka for the older group. No significant relationship was observed in age versus stratigraphy for the 250 m thick older lava section. This suggests a short time span, less than the errors of dating, for the lava accumulation.Primary paleodirections were easily obtained, after cleaning by both AF and thermal demagnetization, from all lavas except two in which a possible effect of lightning was suspected. Paleointensity experiments, using mainly the Shaw method, were made on 15 lavas which showed good stability to thermal demagnetization. In the analysis of the Shaw results, the correction method of Kono (1978) was applied, since most samples showed changes in ARM capacity after heating. The double heating technique of Tsunakawa and Shaw

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Age of the Laschamp paleomagnetic excursion revisited

Cited by 124 publications

References 9 publications

Evidence for large methane releases to the atmosphere from deep-sea gas-hydrate dissociation during the last glacial episode

Evidence for large methane releases to the atmosphere from deep-sea gas-hydrate dissociation during the last glacial episode

Orbital- and millennial-scale environmental changes between 64 and 20 ka BP recorded in Black Sea sediments

K-Ar Ages and Paleosecular Variation of Direction and Intensity from Quaternary Lava Sequences in the Ruapehu Volcano, New Zealand.

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