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  • 1
    Publication Date: 2015-03-01
    Description: To assess the importance of climate variables for the distribution of modern pollen data in China, we present a continental-scale dataset consisting of 1374 samples. Boosted regression trees and constrained ordination techniques are employed to quantify the importance of six climate variables (annual precipitation, PANN; actual/potential evapotranspiration ratio, Alpha; mean annual temperature, TANN; mean temperature of the warmest month, MTWA; mean temperature of the coldest month, MTCO; annual sum of the growing degree days above 5°C, GDD5) for the distribution of individual pollen taxa and modern pollen assemblages. The results show that taxon-specific responses to the climate variables display a wide regional diversity and that the climate variables with low collinearity that best account for the spatial variability of modern pollen assemblages differ regionally. PANN is the most important variable in northwestern and northeastern China and the Tibetan Plateau, while MTWA and MTCO are the dominant variables in east-central and southern China. This suggests that the climate variables that can be optimally reconstructed from fossil pollen data vary in different bioclimatic regions of China. This feature is typical to many continental-scale modern pollen datasets and needs to be considered in pollen-based climate reconstructions.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 2
    Publication Date: 2014-01-01
    Description: In order to test the accuracy of accelerator mass spectrometry (AMS) radiocarbon dating of pollen, 8 samples of pollen concentrates and 4 bulk organic samples were collected and analyzed from trench T1041 at the Tianluoshan site, Yuyao city, Zhejiang Province. This site was chosen because a reliable chronology had been previously established there based on radiocarbon dates of plant materials. The pollen concentrate samples were measured using AMS 14C and the 4 bulk organic samples were measured by liquid scintillation counting (LSC). The pollen concentrates and bulk organic samples yield ages that are a few hundred years to thousands of years older than those from plant materials, respectively. Contributions from reworked sediments can explain the older ages for the pollen concentrates and sediment organic dates. This study suggests that caution must be exercised when discussing millennial- or centennial-scale climate events based on chronologies that are controlled by age determinations of pollen concentrates.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 3
    Publication Date: 2014-01-01
    Description: The rapid outward and upward growth of the world's large fluvial sedimentary systems during the second half of the Holocene is a remarkable geologic process that may have buried considerable areas of pre-existing riparian wetlands, which in turn would sequester massive carbon. However, the role of floodplain lakes in the global carbon budget has long been neglected. This article demonstrates the potential of organic carbon burial due to floodplain aggradation during the late Holocene by analyzing a sediment core from a buried floodplain lake in the lower Yellow River area. Based on detailed radiocarbon dating, this study inferred that landscape development in the study area has experienced three disparate stages closely related to the displacement of the lower Yellow River channel. The first stage (∼2250–1700 cal yr BP) represents a widespread pedogenic process while the Yellow River discharged to the northern Bohai Sea through a course much farther north from the present-day position. The subsequent stage (∼1700–1000 cal yr BP) broadly corresponds to the calm period of the Yellow River while it discharged to the southern Bohai Sea through a course slightly north from the present-day position. A lacustrine environment prevailed during this period, sequestering organic carbon at a rate of ∼0.58 kg m 2 yr 1. The final stage (∼1000 cal yr BP to present) is marked by the rapid growth of the floodplain due to the frequent rerouting of the lower Yellow River. This analysis suggests that fluvial sedimentary systems should be integrated into the terrestrial carbon budget when accounting for the aberrant rise of the atmospheric CO2 in the face of global cooling during the second half of the Holocene.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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