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  • 1
    Language: English
    In: Science (American Association for the Advancement of Science), 2012-07-20, Vol.337 (6092), p.315-320
    Description: The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous "super interglacials" during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ∼4° to 5°C and ∼300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity.
    Subject(s): Arctic Regions ; Arrays ; Climate ; Climate Change ; Climate models ; Climate Research ; Climatic changes ; Cold Climate ; Earth and Related Environmental Sciences ; Environmental aspects ; Freshwater ; Geologic Sediments ; Geological facies ; Geological time ; Geovetenskap och miljövetenskap ; Glacial lakes ; Ice Cover ; Ice sheets ; Klimatforskning ; Lakes ; Latitude ; Meteorites ; Natural Sciences ; Naturvetenskap ; Oceans ; Paleoclimate science ; Paleoclimatology ; Paleolimnology ; Pollen ; Radiometric Dating ; Research ; RESEARCH ARTICLE ; Russia ; Sediments ; Summer ; Time Factors
    ISSN: 0036-8075
    ISSN: 1095-9203
    E-ISSN: 1095-9203
    Source: JSTOR Life Sciences
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
    Source: Get It Now
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  • 2
    Language: English
    In: Nature (London), 2007-01-04, Vol.445 (7123), p.74-77
    Description: The Asian-Australian monsoon is an important component of the Earth's climate system that influences the societal and economic activity of roughly half the world's population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the Bølling-Allerød warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period ad 700 to 900 (refs 4-6), suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.
    Subject(s): Art and archaeology ; Asia ; China ; Climatology. Bioclimatology. Climate change ; Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; External geophysics ; Meteorology ; Paleontology ; Paleontology: general ; Tang dynasty
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Academic Search Ultimate
    Source: Nature Journals Online
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  • 3
    Language: English
    In: International journal of earth sciences : Geologische Rundschau, 2018-10-01, Vol.108 (1), p.267-285
    Description: We report here on results of palaeo- and rock magnetic investigations of two sediment cores from the Upper Congo deep-sea fan. The sediments have a high organic content and contain a heterogeneous Fe-mineral assemblage with biogenic magnetite and detrital (Ti-)magnetite as the main magnetic carrier minerals. Pyrite, hematite, and Fe-oxyhydroxides were identified by comparing high-temperature magnetic susceptibility curves with those from Fe-minerals of known composition. According to AMS 14 C dates, the 6.8 m-long profile spans the last 37 kyr. Sediments older than 20 ka are affected by reductive diagenesis that has led to a loss of the fine-grained magnetic mineral fraction. Sediments younger than 20 ka have stable magnetizations. Characteristic remanent magnetization records of inclination and declination were obtained for each core. There is a little agreement between these records, modelled curves, and other sediment records from Equatorial Africa, so no composite record could be established. The cores are not ideal relative palaeointensity recorders and estimates using different normalizers did not yield consistent signals from both cores. Normalization methods used for relative palaeointensity estimation were not developed for sediments that contain large amounts of ultra-fine-grained biogenic magnetite; therefore, the relative palaeointensity estimates should be considered with caution. However, in view of the incoherent picture given by the scarce available palaeointensity information from the region off South-West Africa, the GeoB6517-2 record may provide a tentative relative palaeointensity record for comparison, at least for the past 10 kyr.
    Subject(s): Analysis ; Diagenesis ; Earth and Environmental Science ; Earth Sciences ; Geochemistry ; Geology ; Geophysics/Geodesy ; Geosciences, Multidisciplinary ; Hematite ; Investigations ; Magnetite ; Magnetization ; Mineral Resources ; Original Paper ; Physical Sciences ; Science & Technology ; Sedimentology ; Sediments (Geology) ; Structural Geology ; Sulfur compounds
    ISSN: 1437-3254
    E-ISSN: 1437-3262
    Source: Academic Search Ultimate
    Source: Web of Science - Science Citation Index Expanded - 2019〈img src="http://exlibris-pub.s3.amazonaws.com/fromwos-v2.jpg" /〉
    Source: Alma/SFX Local Collection
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  • 4
    Language: English
    In: Biogeosciences, 2016-04-08, Vol.13 (7), p.2093-2109
    Description: The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial–interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before ∼  320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial–interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial–interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.
    ISSN: 1726-4189
    ISSN: 1726-4170
    E-ISSN: 1726-4189
    Source: DOAJ Directory of Open Access Journals - Not for CDI Discovery
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  • 5
    Language: English
    In: Tectonics (Washington, D.C.), 2008-11-07, Vol.27 (6), p.TC6001-n/a
    Description: The southern Alborz mountains of northern Iran are an integral part of the Arabia/Eurasia collision zone. A magnetostratigraphic and rock magnetic investigation of the Eyvanekey stratigraphic section in the southern Alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the Alborz foreland basin. The section constitutes three coarsening upward units (units 1, 2, and 3), comprising the Upper Red and Hezardarreh formations. Our data reveal that the Upper Red Formation was deposited between 17.5 and 7.5 Ma, while the depositional age of the top of the Hezardarreh Formation can be extrapolated to ∼6.2 Ma. Slow sediment accumulation rates correlate with sedimentary facies comprising prograding, coarsening‐upward units. This is likely the result of intraforeland uplift (units 1 and 2) and basin inversion, probably associated with a growth syncline located in the proximal foreland (unit 3). In contrast, fine‐grained strata at the bottom of each cycle are associated with faster sediment accumulation rates, testifying to enhanced flexural basin subsidence in the course of thrust loading. Progradation of coarse‐grained facies also occurred during relatively fast sediment accumulation (top of unit 2), suggesting that the influx of coarse‐grained sediment outpaced the storage capacity of the proximal foreland. Thus, despite an overall southward propagation of deformation into the southern Alborz foreland, the locus of active deformation must have migrated back and forth on a time scale of circa 0.7 to 2 Ma.
    Subject(s): Alborz mountains ; Biological and Chemical ; coarsening upward unit ; compressional ; Continental tectonics ; Facies (Geology) ; foreland basin system ; Geomagnetism and Paleomagnetism ; Magnetostratigraphy ; Natural history ; northern Iran ; Oceanography ; sediment accumulation rate ; Sedimentary basin processes ; Sedimentary basins ; Sedimentation ; Structure ; Tectonophysics
    ISSN: 0278-7407
    E-ISSN: 1944-9194
    Source: Wiley Online Library All Backfiles
    Source: Elektronische Zeitschriftenbibliothek - Frei zugängliche E-Journals
    Source: Wiley-Blackwell Full Collection 2014
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  • 6
    Language: English
    In: Journal of geophysical research. Solid earth, 2020-08, Vol.125 (8), p.n/a
    Description: A full‐vector paleomagnetic record, comprising directional data and relative paleointensity (rPI), was derived from 16 sediment cores recovered from the southeastern Black Sea. The obtained data were used to create a stack covering the time window between 68.9 and 14.5 ka. Age models are based on radiocarbon dating and correlations of warming/cooling cycles monitored by high‐resolution X‐ray fluorescence (XRF) elementary ratios and by ice‐rafted debris (IRD) in Black Sea sediments to the sequence of “Dansgaard‐Oeschger” (D‐O) events defined from the Greenland ice core oxygen isotope stratigraphy. The reconstructed prominent lows in paleointensity at about 64.5, 41.2, and 34.5 ka are coeval with the Norwegian‐Greenland Sea, the Laschamps, and the Mono Lake excursions, respectively. For a further analysis, the stacked Black Sea paleomagnetic record was converted into one component being parallel to the direction expected from a geocentric axial dipole (GAD) and two components perpendicular to it (EW, inclined NS), representing definitely only non‐GAD components of the geomagnetic field. Discussions of the field configurations at the Black Sea site are focused on the three excursional events. The Norwegian‐Greenland Sea excursion was dominated by a decaying axial dipole and persisting weak nondipole field, with directional variations still within the range of normal secular variations. The Laschamps excursion comprises two full polarity transitions and a short stable interval of reversed polarity in between. The Mono Lake excursion was mostly dominated by a nondipole field, though with a less pronounced weakening of the axial dipole component. Key Points Reconstructed paleosecular variation record between 68.9 and 14.5 ka from Black Sea sediments Increasing axial dipole component with reversed polarity during the midpoint of the Laschamps excursion Comparable levels of dipole and nondipole contributions during the Mono Lake excursion
    Subject(s): Black Sea ; Laschamps excursion ; Mono Lake excursion ; Norwegian‐Greenland Sea excursion ; paleosecular variations
    ISSN: 2169-9313
    E-ISSN: 2169-9356
    Source: Alma/SFX Local Collection
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  • 7
    Language: English
    In: Frontiers in earth science (Lausanne), 2018-10-25, Vol.6
    Description: The large and well-studied archaeological record of Israel offers a unique opportunity for collecting high resolution archaeomagnetic data from the past several millennia. Here, we initiate the first catalog of archaeomagnetic directions from Israel, with data covering the past four millennia. The catalog consists of 76 directions, of which 47 fulfill quality selection criteria with Fisher precision parameter (k) ≥ 60, 95% cone of confidence (α95) 〈 6° and number of specimens per site (n) ≥ 8. The new catalog complements our published paleointensity data from the Levant and enables testing the hypothesis of a regional geomagnetic anomaly in the Levant during the Iron Age proposed by Shaar et al. (2016, 2017). Most of the archaeomagnetic directions show 〈 15° angular deviations from an axial dipole field. However, we observe in the tenth and ninth century BCE short intervals with field directions that are 19°-22° different from an axial dipole field and inclinations that are 20°-22° steeper than an axial dipole field. The beginning of the first millennium BCE is also characterized with fast secular variation rates. The new catalog provides additional support to the Levantine Iron Age Anomaly hypothesis.
    Subject(s): Archaeology ; archaeomagnetism ; Catalogs ; Earth Sciences ; geomagnetic field ; geomagnetic secular variations ; Geophysics ; Israel ; levantine Iron-Age Anomaly ; paleomagnetism ; Sciences of the Universe
    ISSN: 2296-6463
    E-ISSN: 2296-6463
    Source: Alma/SFX Local Collection
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  • 8
    Language: English
    In: Geophysical journal international, 2011-10, Vol.187 (1), p.34-44
    Description: SUMMARY Magnetic extracts obtained from sediment cores recovered from Lake Kinneret, Israel, were subjected to comprehensive scanning electron microscope and in‐line energy dispersive X‐ray spectroscopy analyses. A variety of ferrimagnetic iron oxides and iron sulphide particles were identified, along with apparently non‐magnetic iron sulphides. The majority of the iron oxides are titanomagnetites that have undergone pervasive dissolution, and in many cases were only preserved as skeletal, 3‐D lattices of ilmenite lamellae. Often the spaces between the submicron ilmenite lamellae are empty. Also sponge‐like dissolution features are observed in some residual titanomagnetite grains. Another group of titanomagnetite grains is characterized by superficial shrinkage‐cracks, which indicate low‐temperature maghemitization. In some cases, these cracks appear to be where dissolution started. Most titanomagnetites contain impurities of Al, Mg, Si and Mn on the order of 1 per cent. Chromium‐magnetites, with minor Ti, Mg and Al content on the order of a few percent, but without Mn, were also found. Chromium‐magnetites mostly occur as octahedra in a well‐preserved state, which indicates that they are less prone to dissolution. Magnetite spherules of 40–60 μm in size, which were mostly hollow, were only found in material collected from the outer zone of the core section that was in contact with the steel core barrel. These spherules were not found in material collected from the centre of the core. They are therefore interpreted as contaminants that were produced during fabrication of the steel core barrel. Iron sulphides are present as pyrite, either as larger aggregates of cubic crystals, each of up to 20 μm in size, or as 5–10 μm framboidal aggregates, consisting mostly about 0.3 μm idiomorphic octahedra. The cubic pyrite crystals have heterogeneous compositions. Pure pyrite should be non‐magnetic, but even aggregates of up to 150 μm in size were magnetically separated. They probably therefore contain a magnetic core of greigite or overgrown titanomagnetite. The latter possibility is supported by observations of residual titanomagnetites with individual pyrite crystals residing directly on their surfaces, or filling space between ilmenite lamellae. Irregular aggregates of flaky, submicron iron sulphides were also found, which are interpreted to be greigite. The greigite has a low degree of visible crystallization. Pyrite and/or greigite grains were found inside the aggregates, or in agglomerates with organic remnants. Together, visual observations and elemental analyses provide clear evidence of pervasive dissolution of primary titanomagnetite and concurrent sulphidization of sediments from Lake Kinneret.
    Subject(s): Aggregates ; Dissolution ; Ilmenite ; Iron ; Landscape evolution ; Magnetic mineralogy and petrology ; Magnetite ; Magnetostratigraphy ; Oxides ; Pyrite ; Rock and mineral magnetism ; Scanning electron microscopy ; Sediments ; Sediments (Geology) ; Sulfides ; Sulfur compounds
    ISSN: 0956-540X
    E-ISSN: 1365-246X
    Source: Oxford Journals Current Collection
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  • 9
    Language: English
    In: Journal of paleolimnology, 2006-12-27, Vol.37 (1), p.65-76
    Description: Byline: Norbert R. Nowaczyk (1), Martin Melles (2), Pavel Minyuk (3) Keywords: Solar forcing; Magnetic susceptibility; Lake El'gygytgyn; Siberia; Lake sediments A combined analysis of magnetic susceptibility, total organic carbon (TOC), biogenic silica (opal), and TiO.sub.2 content of the 12.6 m long composite core PG1351 recovered from Lake El'gygytgyn, Chukotka Peninsula, indicate a clear response of the lacustrine sedimentary record to climate variations. The impact is not direct, but through variations in oxygenation of the bottom waters. Mixing of the water body is typical for warmer climates, whereas the development of a stratified water body associated with anoxic conditions at the lake floor appears during cold climates. Oxic conditions lead to a good magnetite preservation and thus to high magnetic susceptibilities, but also to a large-scale degradation of organic matter, as reflected by low TOC (total organic carbon) values. During anoxic conditions, magnetite is severely dissolved yielding very low susceptibility values, whereas organic matter is best preserved, reflected by high TOC values. Hence, in general, neither susceptibility reflects the lithogenic fraction, nor does TOC reflect bioproductivity in case of the studied El'gygytgyn sediments. Based on available infrared stimulated luminescence (IRSL) dating, the obtained susceptibility pattern of core PG1351 shows an obvious correlation to northern hemisphere insolation variations, with a dominating impact of the Earth's 18 and 23 kyr precessional cycles for the upper half of PG1351, that is, during the past 150 ka. Therefore, the whole susceptibility record, together with biogenic silica (as a proxy for bioproductivity), TOC (as an indicator for redox conditions), and TiO.sub.2 (as a proxy for lithogenic input), was systematically tuned to the northern hemisphere insolation yielding an age of about 250 ka for the base of the composite core. Author Affiliation: (1) GeoForschungsZentrum Potsdam, Section 3.3 -- "Climate Dynamics and Sediments", Telegrafenberg Haus C, D-14474, Potsdam, Germany (2) Institute for Geophysics and Geology, University Leipzig, Talstrasse 35, D-04103, Leipzig, Germany (3) North-East Interdisciplinary Science Research Institute (NEISRI), Russian Academy of Sciences, 16 Portovaya St., 685000, Magadan, Russia Article History: Registration Date: 08/05/2006 Received Date: 09/09/2004 Accepted Date: 01/05/2005 Online Date: 25/08/2006 Article note: This is the fifth in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.
    Subject(s): Analysis ; Disease susceptibility
    ISSN: 0921-2728
    E-ISSN: 1573-0417
    Source: Alma/SFX Local Collection
    Source: ProQuest Central
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  • 10
    Language: English
    In: Journal of paleolimnology, 2006-12-27, Vol.37 (1), p.89-104
    Description: Byline: Martin Melles (1), Julie Brigham-Grette (2), Olga Yu. Glushkova (3), Pavel S. Minyuk (3), Norbert R. Nowaczyk (4), Hans-W. Hubberten (5) Keywords: Siberian Arctic; Quaternary; Paleolimnology; Paleoclimate; Organic geochemistry; Carbon isotopes The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El'gygytgyn, NE Siberia, was investigated for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios ([delt[a].sup.13]C.sub.TOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation, thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate, resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1--7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions. During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall, and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more snow cover onaPSthe perennial ice, strongly reducing light penetration and biogenic primary production inaPSthe lake. While the cold--warm pattern duringaPSthe past three glacial--interglacial cycles is probably controlled by changes in regional summer insolation, differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely were due to changes in atmospheric circulation patterns. Author Affiliation: (1) Institute for Geophysics and Geology, University Leipzig, Talstrasse 35, D-04103, Leipzig, Germany (2) Department of Geosciences, University of Massachusetts, Morrill Science Building, Box 35820, Amherst, MA, 01003, USA (3) North East Interdisciplinary Research Institute Far East Branch, Russian Academy of Sciences, 16 Portovaya Street, Magadan, 685000, Russia (4) GeoForschungsZentrum, Telegrafenberg C321, D-14473, Potsdam, Germany (5) Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Telegrafenberg A43, D-14473, Potsdam, Germany Article History: Registration Date: 08/05/2006 Received Date: 09/02/2004 Accepted Date: 09/08/2005 Online Date: 09/12/2006 Article note: This is the seventh in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. JulieBrigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.
    ISSN: 0921-2728
    E-ISSN: 1573-0417
    Source: Alma/SFX Local Collection
    Source: ProQuest Central
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