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1.
Amaelle Landais Valérie Masson-Delmotte Jean Jouzel Dominique Raynaud Sigfus Johnsen Christof Huber Markus Leuenberger Jakob Schwander Bénédicte Minster 《Climate Dynamics》2006,26(2-3):273-284
The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated
climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show
that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception (∼123–100 kyears
BP) encompassing Dansgaard–Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out
disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of
10±2.5 and 16±2.5°C, amplitudes which mimic those observed in full glacial conditions. We use records of δ18O of O2 to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years,
and to examine the interhemispheric sequence of events over this period. After a synchronous North–South temperature decrease,
the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic
counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to
intermediate levels of CO2 and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24
and 23 appear similar to typical full glacial DO events. 相似文献
2.
Summary Barylite has been identified for the first time in Greenland in several specimens from the nepheline syenite pegmatite pockets at Narssârssuk. The crystals are orthorhombic, showing the forms {100}, {210} and {201}, and form thin plates parallel to {100}. Electron microprobe analysis and emission spectrography show a composition close to the ideal formula. The refined unit cell paramters are:a=9.835(2) Å,b=11.654(3) Å andc=4.673(1) Å. The barylite is biaxial negative, 2V
=66o±2o,n
=1.694,n
= 1.697 andn
calc.=1.698.
Das erste grönländische Vorkommen des seltenen Minerales Barylith
Zusammenfassung Der seltene Barylith wurde zum ersten Mal in Grönland in verschiedenen Proben aus Nephelin-Syenit-Pegmatit-Drusen bei Narssârssuk identifiziert. Die Kristalle sind orthorhombisch mit den Formen {100}, {210} und {201}, sie bilden dünne Tafeln nach {100}. Elektronensonden-Analyse und Emissions-Spektrographie ergeben eine chemische Zussammensetzung, die der Idealform nahekommt. Die verfeinerten Zellparameter sind folgende:a=9,835(2) Å,b=11,654(3) Å undc=4,673(1) Å. Barylith ist zweiachsig negativ, 2V =66o±2o,n =1,694,n =1.697 undn calc.= 1,698.相似文献
3.
Independent calendar year chronologies are a basic requirement for the establishment of high resolution land-ice teleconnections.
The annually laminated Meerfelder Maar record provides both an independent chronology, established by varve counting, and
high resolution lithological proxy data for the period of the last Glacial/Interglacial transition. These data reveal a series
of four periods of climatic deterioration coinciding with negative isotopic deviations in the GRIP record signal, thus demonstrating
the synchronicity of environment changes in Western Germany and temperature shifts in Greenland. The terrestrial data supports
a further sub-division of the event stratigraphy based on the GRIP core, by introducing the cold event GI-1c2 between 13 500
and 13 400 calendar years BP. Multiproxy analyses reveal that the environmental response at Meerfelder Maar was not linear
throughout the Lateglacial but was modified by local processes. A change in the response of the lake environment to climate
deterioration was observed during sub-stage GI-1b (Gerzensee oscillation), the only event with gradual rather than abrupt
transitions. The two-fold character of the Younger Dryas as seen in the GRIP record is more pronounced in the Meerfelder Maar
record. This lithological signal occurred with a delay of 60 years to the GRIP signal, and has been linked to a shift in the
catchment. It is proposed that the trigger for this shift was a trend towards a more humid second half of the Younger Dryas.
Received: 21 May 1999 / Accepted: 18 August 1999 相似文献
4.
Rate coefficients for the association reactions of NO+ ions with N2 and CO2, O2+ with N2, and N+ and N2+ with N2 have been determined as a function of gas temperature in a laboratory experiment employing a variable-temperature drift-tube apparatus. The measured rate coefficients were fitted to power laws of the form where the exponents x ranged from 2.2 to 4.3. The strong temperature dependence observed in the case of the reaction of NO+ with N2 (x = 4.3) supports the thesis by Arnold et al. (1979) that the temperature variability of D-region ion densities is a result of this reaction step in the ion clustering sequence. 相似文献
5.
Jeffrey A. Macdonald Manfred A. Biondi Rainer Johnsen 《Planetary and Space Science》1984,32(5):651-654
The dissociative recombination coefficients α for capture of electrons by H3+ and H5+ ions have been determined as a function of electron temperature Te using a microwave afterglow-mass spectrometer apparatus. At ion and neutral temperatures Tu+ = Tn = 240 K, the coefficient α (H3+) is found to vary slowly with Te at first, decreasing from 1.6 × 10?7 cm3/s at Te = 240 K to 1.2 × 10?7 cm3/s at Te = 500 K, thereafter falling as Te?1 over the range 500 K ? Te, ? 3000 K. These results, which have a ± 20% uncertainty, agree satisfactorily over the common energy range (0.03–0.36 eV) with the recombination cross sections determined in merged beam measurements by Auerbach et al. At T+ = Tn = 128 K, the coefficient α(H5+) is found to be (1.8 ± 0.3) × 10?6 [Te(K)/300]?0.69 cm3/s over the range 128 K ? Te ? 3000 K, with a more rapid decrease, as Te?1, between 3000 K and 5500 K. The implications of these results for modelling planetary atmospheres and interstellar clouds are briefly touched on. 相似文献
6.
Cessation of the Norwegian drift net fishery: changes observed in Norwegian and Russian populations of Atlantic salmon 总被引：3，自引：2，他引：1
7.
Mike Walker Sigfus Johnsen Sune Olander Rasmussen Trevor Popp Jørgen‐Peder Steffensen Phil Gibbard Wim Hoek John Lowe John Andrews Svante Björck Les C. Cwynar Konrad Hughen Peter Kershaw Bernd Kromer Thomas Litt David J. Lowe Takeshi Nakagawa Rewi Newnham Jakob Schwander 《第四纪科学杂志》2009,24(1):3-17
The Greenland ice core from NorthGRIP (NGRIP) contains a proxy climate record across the Pleistocene–Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision. This climatic event is most clearly reflected in an abrupt shift in deuterium excess values, accompanied by more gradual changes in δ18O, dust concentration, a range of chemical species, and annual layer thickness. A timescale based on multi‐parameter annual layer counting provides an age of 11 700 calendar yr b2 k (before AD 2000) for the base of the Holocene, with a maximum counting error of 99 yr. A proposal that an archived core from this unique sequence should constitute the Global Stratotype Section and Point (GSSP) for the base of the Holocene Series/Epoch (Quaternary System/Period) has been ratified by the International Union of Geological Sciences. Five auxiliary stratotypes for the Pleistocene–Holocene boundary have also been recognised. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
8.
Katrine K. Andersen Anders Svensson Sigfus J. Johnsen Sune O. Rasmussen Matthias Bigler Regine Rthlisberger Urs Ruth Marie-Louise Siggaard-Andersen Jrgen Peder Steffensen Dorthe Dahl-Jensen Bo M. Vinther Henrik B. Clausen 《Quaternary Science Reviews》2006,25(23-24):3246
The Greenland Ice Core Chronology 2005, GICC05, is extended back to 42 ka b2k (before 2000 AD), i.e. to the end of Greenland Stadial 11. The chronology is based on independent multi-parameter counting of annual layers using comprehensive high-resolution measurements available from the North Greenland Ice Core Project, NGRIP. These are measurements of visual stratigraphy, conductivity of the solid ice, electrolytical melt water conductivity and the concentration of Na+, Ca2+, SO42−, NO3−, NH4+. An uncertainty estimate of the time scale is obtained from identification of ‘uncertain’ annual layers, which are counted as 0.5±0.5 years. The sum of the uncertain annual layers, the so-called maximum counting error of the presented chronology ranges from 4% in the warm interstadial periods to 7% in the cold stadials. The annual accumulation rates of the stadials and interstadials are on average one-third and half of the present day values, respectively, and the onset of the Greenland Interstadials 2, 3, and 8, based on 20 year averaged δ18O values, are determined as 23,340, 27,780, and 38,220 yr b2k in GICC05. 相似文献
9.
A. Aldahan G. Possnert S. J. Johnsen H. B. Clausen E. Isaksson W. Karlen M. Hansson 《Journal of Earth System Science》1998,107(2):139-147
We report in this study the distribution of10Be in the top 40 m of the Renland ice core (East Greenland) and in a 30 m long core from DML (Dronning Maud Land, Antarctica)
for the period 1931–1988. The two sites show differences in10Be content, the Antarctica site showing smaller variance and a lower average10Be annual flux. Similarly, the average accumulation rate (cm water equivalent year−1) is higher in the Renland relative to DML. The variability in accumulation (precipitation) rates seems to explain part of
the difference in10Be flux between the two polar sites. Cyclic fluctuations of10Be flux correlate with the 11-year sunspot number and cosmic ray intensity than with the aa index (perturbation of the geomagnetic
activity by the solar wind). Our data corroborate10Be cyclic fluctuation pattern from the Dye 3 ice core and confirm a promising potential for correlation of global and local
events. 相似文献
10.
Valrie Masson Franoise Vimeux Jean Jouzel Vin Morgan Marc Delmotte Philippe Ciais Claus Hammer Sigfus Johnsen Vladimir Ya. Lipenkov E. Mosley-Thompson Jean-Robert Petit Eric J. Steig Michel Stievenard Rein Vaikmae 《Quaternary Research》2000,54(3):348
A comparison is made of the Holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east Antarctica (Vostok, Dome B, Plateau Remote, Komsomolskaia, Dome C, Taylor Dome, Dominion Range, D47, KM105, and Law Dome) and west Antarctica (Byrd), with temporal resolution from 20 to 50 yr. The long-term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations. All the records confirm the widespread Antarctic early Holocene optimum between 11,500 and 9000 yr; in the Ross Sea sector, a secondary optimum is identified between 7000 and 5000 yr, whereas all eastern Antarctic sites show a late optimum between 6000 and 3000 yr. Superimposed on the long time trend, all the records exhibit 9 aperiodic millennial-scale oscillations. Climatic optima show a reduced pacing between warm events (typically 800 yr), whereas cooler periods are associated with less-frequent warm events (pacing >1200 yr). 相似文献