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  • Articles  (112)
  • 2015-2019
  • 2010-2014  (112)
  • 2013  (112)
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  • Articles  (112)
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  • 2015-2019
  • 2010-2014  (112)
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  • 1
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    Trace-element variations in an annually layered stalagmite as recorders of climatic changes and anthropogenic pollution in Central China (2013)
    Cambridge University Press
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    Publication Date: 2013-12-29
    Description: Publication date: Available online 28 December 2013 Source: Quaternary Research Author(s): Liangcheng Tan , Chuan-Chou Shen , Yanjun Cai , Li Lo , Hai Cheng , Zhisheng An We analyzed variations in the Sr/Ca, Ba/Ca, REE/Ca (REE: rare earth element), Zn/Ca, and Pb/Ca ratios preserved in an annually layered stalagmite, XL21, from central China. The stalagmite record spans the 95 year period AD 1914–2008. The Sr/Ca and Ba/Ca ratios have a significant positive correlation with the stalagmite's growth rate, suggesting that they were primarily controlled by growth-rate variations. Variations in REE/Ca ratios are consistent with local temperature changes, suggesting temperature influenced REE concentrations in the stalagmite over decadal to annual timescales. Higher temperature in this humid area can increase vegetation cover, microbial activity, and organic decomposition in the soil, resulting in enhanced pCO 2 , organic matter concentration and reduced pH, and consequently increased REE mobilization from the overlying soil layer and host rock. Higher temperatures may also increase the natural Zn mobilization from the overlying soil mediated by organic matter and consequently may have led to increased Zn retention in XL21. An increasing trend is seen in the Pb/Ca ratios from XL21 since 1985, which is consistent with increased lead production in this area, and indicates an increase in mine-derived lead pollution in the local environment over the past 30 years.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
    Published by Cambridge University Press
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  • 2
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    Out-of-phase evolution between summer and winter East Asian monsoons during the Holocene as recorded by Chinese loess deposits (2013)
    Cambridge University Press
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    Publication Date: 2013-12-24
    Description: Publication date: Available online 23 December 2013 Source: Quaternary Research Author(s): Dunsheng Xia , Jia Jia , Guanhua Li , Shuang Zhao , Haitao Wei , Fahu Chen We analyzed climate proxies from loessic-soil sections of the southern Chinese Loess Plateau. The early Holocene paleosol, S0, is 3.2 m thick and contains six sub-soil units. Co-eval soils from the central Loess Plateau are thinner (~ 1 m). Consequently higher-resolution stratigraphic analyses can be made on our new sections and provide more insight into Holocene temporal variation of the East Asian monsoon. Both summer and winter monsoon evolution signals are recorded in the same sections, enabling the study of phase relationships between the signals. Our analyses consist of (i) measurements of magnetic properties sensitive to the production of fine-grained magnetic minerals which reflect precipitation intensity and summer monsoon strength; and (ii) grain-size analyses which reflect winter monsoon strength. Our results indicate that the Holocene precipitation maximum occurred in the mid-Holocene, ~ 7.8–3.5 cal ka BP, with an arid interval at 6.3–5.3 cal ka BP. The winter monsoon intensity declined to a minimum during 5.0–3.4 cal ka BP. These results suggest that the East Asian summer and winter monsoons were out of phase during the Holocene, possibly due to their different sensitivities to ice and snow coverage at high latitudes and to sea-surface temperature at low latitudes.
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    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 3
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    Terminal Pleistocene change in mammal communities in southeastern Washington State, USA (2013)
    Cambridge University Press
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    Publication Date: 2013-12-23
    Description: Publication date: Available online 22 December 2013 Source: Quaternary Research Author(s): R. Lee Lyman Small mammal communities in western North America experienced declines in taxonomic richness across the late Pleistocene to Holocene transition (PHT), a recent natural global warming event. One community also experienced a decline in evenness and others replaced one species with a congener. Variability in response of small mammal communities to PHT warming is apparent. At the presently arid and xeric Marmes site in the Columbia Basin of southeastern Washington State, megafauna were absent by about 13,000 cal yr BP, evenness of small mammals declined about 11,700 cal yr BP and again about 11,400 cal yr BP whereas richness declined about 11,400 cal BP. Regional faunal turnover was, however, minimal among small-bodied taxa. Local mammal communities are depauperate as a result of megafaunal extinctions and subsequent decreases in small-mammal richness and evenness. The latter chronologically corresponds with a decrease in primary productivity driven by increasing warmth and aridity. More faunas must be studied in order to fully document the range of variability in the responses of mammalian communities to PHT warming. Documentation of patterns in those responses will facilitate understanding and enhance predictive accuracy with respect to responses of mammalian communities to modern global warming.
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    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 4
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    Glacial and periglacial buzzsaws: fitting mechanisms to metaphors (2013)
    Cambridge University Press
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    Publication Date: 2013-12-19
    Description: Publication date: Available online 18 December 2013 Source: Quaternary Research Author(s): Adrian M. Hall , Johan Kleman
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    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 5
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    Geochronology and paleoenvironment of pluvial Harper Lake, Mojave Desert, California, USA (2013)
    Cambridge University Press
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    Publication Date: 2013-12-17
    Description: Publication date: Available online 16 December 2013 Source: Quaternary Research Author(s): Anna L. Garcia , Jeffrey R. Knott , Shannon A. Mahan , Jordon Bright Accurate reconstruction of the paleo-Mojave River and pluvial lake (Harper, Manix, Cronese, and Mojave) system of southern California is critical to understanding paleoclimate and the North American polar jet stream position over the last 500 ka. Previous studies inferred a polar jet stream south of 35°N at 18 ka and at ~ 40°N at 17–14 ka. Highstand sediments of Harper Lake, the upstream-most pluvial lake along the Mojave River, have yielded uncalibrated radiocarbon ages ranging from 24,000 to > 30,000 14 C yr BP. Based on geologic mapping, radiocarbon and optically stimulated luminescence dating, we infer a ~ 45–40 ka age for the Harper Lake highstand sediments. Combining the Harper Lake highstand with other Great Basin pluvial lake/spring and marine climate records, we infer that the North American polar jet stream was south of 35°N about 45–40 ka, but shifted to 40°N by ~ 35 ka. Ostracodes ( Limnocythere ceriotuberosa ) from Harper Lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the Mojave River, thus confirming the lake was fed by the Mojave River. The ~ 45–40 ka highstand at Harper Lake coincides with a shallowing interval at downstream Lake Manix.
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    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 6
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    Assessing soil erosion and control factors by radiometric technique in the source region of the Yellow River, Tibetan Plateau (2013)
    Cambridge University Press
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    Publication Date: 2013-12-15
    Description: Publication date: Available online 14 December 2013 Source: Quaternary Research Author(s): Yibo Wang , Fujun Niu , Qingbai Wu , Zeyong Gao Measurements of 137 Cs concentration in soils were made in a representative catchment to quantify erosion rates and identify the main factors involved in the erosion in the source region of the Yellow River in the Tibetan Plateau. In order to estimate erosion rates in terms of the main factors affecting soil loss, samples were collected taking into account the slope and vegetation cover along six selected transects within the Dari County catchment. The reference inventory for the area was established at a stable, well-preserved, site of small thickness (value of 2324 Bq·m − 2 ). All the sampling sites had been eroded and 137 Cs inventories varied widely in the topsoil (14.87–25.56 Bq·kg − 1 ). The effective soil loss values were also highly variable (11.03–28.35 t·km − 1 ·yr − 1 ) in line with the vegetation cover change. The radiometric approach was useful in quantifying soil erosion rates and examining patterns of soil movement.
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    Topics: Geography , Geosciences
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  • 7
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    Sea-level and reef accretion history of Marine Oxygen Isotope Stage 7 and late Stage 5 based on age and facies of submerged late Pleistocene reefs, Oahu, Hawaii (2013)
    Cambridge University Press
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    Publication Date: 2013-12-13
    Description: Publication date: Available online 12 December 2013 Source: Quaternary Research Author(s): Clark E. Sherman , Charles H. Fletcher , Ken H. Rubin , Kathleen R. Simmons , Walter H. Adey In situ Pleistocene reefs form a gently sloping nearshore terrace around the island of Oahu. TIMS Th–U ages of in situ corals indicate that most of the terrace is composed of reefal limestones correlating to Marine Oxygen Isotope Stage 7 (MIS 7, ~ 190–245 ka). The position of the in situ MIS 7 reef complex indicates that it formed during periods when local sea level was ~ 9 to 20 m below present sea level. Its extensiveness and geomorphic prominence as well as a paucity of emergent in situ MIS 7 reef-framework deposits on Oahu suggest that much of MIS 7 was characterized by regional sea levels below present. Later accretion along the seaward front of the terrace occurred during the latter part of MIS 5 (i.e., MIS 5a–5d, ~ 76–113 ka). The position of the late MIS 5 reefal limestones is consistent with formation during a period when local sea level was below present. The extensiveness of the submerged Pleistocene reefs around Oahu compared to the relative dearth of Holocene accretion is due to the fact that Pleistocene reefs had both more time and more accommodation space available for accretion than their Holocene counterparts.
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  • 8
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    Millennial- to centennial-scale climate periodicities and forcing mechanisms in the westernmost Mediterranean for the past 20,000yr (2013)
    Cambridge University Press
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    Publication Date: 2013-12-12
    Description: Publication date: Available online 11 December 2013 Source: Quaternary Research Author(s): Marta Rodrigo-Gámiz , Francisca Martínez-Ruiz , Francisco J. Rodríguez-Tovar , Francisco J. Jiménez-Espejo , Eulogio Pardo-Igúzquiza Cyclostratigraphic analysis conducted on a continuous high-resolution marine record from the western most Mediterranean reveals well-identified paleoclimate cycles for the last 20,000 yr. The detrital proxies used (Si/Al, Ti/Al, Zr/Al, Mg/Al, K/Al, Rb/Al) are related to different sediment-transport mechanisms, including eolian dust and fluvial runoff, which involve fluctuations in the atmosphere–hydrosphere systems. These fluctuations are accompanied by changes in marine productivity (supported by Ba/Al) and bottom-water redox conditions (Cu/Al, V/Al, Zn/Al, Fe/Al, Mn/Al, U/Th). Spectral analysis conducted using the Lomb–Scargle periodogram and the achieved significance level implemented with the permutation test allowed us to establish major periodicities at 1300, 1515, 2000, and 5000 yr, and secondary peaks at 650, 1087, and 3000 yr. Some of these cycles also agree with those previously described in the North Atlantic Ocean and circum-Mediterranean records. The periodicities obtained at 2000 and 5000 yr support a global connection with records distributed at high, mid, and low latitudes associated with solar activity, monsoonal regime and orbital forcing. The 1300- and 1515-yr cycles appear to be linked with North Atlantic climate variability and the African monsoon system. Thus, the analyzed record provides evidence of climate cycles and plausible forcing mechanisms coupled with ocean–atmosphere fluctuations.
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  • 9
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    Quaternary structural partitioning within the rigid Tarim plate inferred from magnetostratigraphy and sedimentation rate in the eastern Tarim Basin in China (2013)
    Cambridge University Press
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    Publication Date: 2013-12-08
    Description: Publication date: Available online 7 December 2013 Source: Quaternary Research Author(s): Hong Chang , Zhisheng An , Weiguo Liu , Hong Ao , Xiaoke Qiang , Yougui Song , Zhongping Lai It has been proposed that within the Tarim Basin tectonic activity has been limited since Triassic time. However, on the basis of magnetostratigraphy from the eastern Tarim Basin, which defines the chronology of sedimentation and structural evolution of the basin, we show that the basin interior has been uplifted and partitioned during Quaternary. The magnetostratigraphy was constructed from 2228 samples that yielded acceptable inclination values. Characteristic remnant magnetization (ChRM) with both normal (N1–N11) and reversed (R1–R11) polarity was isolated by thermal demagnetization. The data correlate best with polarity chrons C3r to C1n, which range from 5.39 Ma to recent on the geological time scale 2004 (GTS2004). An abrupt decrease in the sedimentation rate is observed at 1.77 Ma in the Ls1 core. This change does not overlap with known Pleistocene climate-change events. We attribute this sedimentation rate decrease to a structurally controlled local decrease in accommodation space where basin basement uplifts occur. This period of sedimentary environmental change reveals that structural partitioning in the basement of the Tarim Basin occurred since ~ 1.77 Ma, and we speculate that tilting of the Southeast Uplift (a sub-basin unit) within the Tarim Basin began in early Pleistocene time.
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  • 10
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    Paleoclimate record in the Nubian Sandstone Aquifer, Sinai Peninsula, Egypt (2013)
    Cambridge University Press
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    Publication Date: 2013-12-05
    Description: Publication date: Available online 4 December 2013 Source: Quaternary Research Author(s): Abdou Abouelmagd , Mohamed Sultan , Neil C. Sturchio , Farouk Soliman , Mohamed Rashed , Mohamed Ahmed , Alan E. Kehew , Adam Milewski , Kyle Chouinard Sixteen groundwater samples collected from production wells tapping Lower Cretaceous Nubian Sandstone and fractured basement aquifers in Sinai were analyzed for their stable isotopic compositions, dissolved noble gas concentrations (recharge temperatures), tritium activities, and 14 C abundances. Results define two groups of samples: Group I has older ages, lower recharge temperatures, and depleted isotopic compositions (adjusted 14 C model age: 24,000–31,000 yr BP; δ 18 O: − 9.59‰ to − 6.53‰; δ 2 H: − 72.9‰ to − 42.9‰; 〈 1 TU; and recharge T: 17.5–22.0°C) compared to Group II (adjusted 14 C model age: 700–4700 yr BP; δ 18 O: − 5.89‰ to − 4.84‰; δ 2 H: − 34.5‰ to − 24.1‰; 〈 1 to 2.78 TU; and recharge T: 20.6–26.2°C). Group II samples have isotopic compositions similar to those of average modern rainfall, with larger d-excess values than Group I waters, and locally measurable tritium activity (up to 2.8 TU). These observations are consistent with (1) the Nubian Aquifer being largely recharged prior to and/or during the Last Glacial Maximum (represented by Group I), possibly through the intensification of paleowesterlies; and (2) continued sporadic recharge during the relatively dry and warmer interglacial period (represented by Group II) under conditions similar to those of the present.
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    Topics: Geography , Geosciences
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