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  • 1
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    A late Holocene paleoenvironmental reconstruction from Agua Caliente, southern Belize, linked to regional climate variability and cultural change at the Maya polity of Uxbenká (2014)
    Cambridge University Press
    Details
    Publication Date: 2014-07-01
    Description: We report high-resolution macroscopic charcoal, pollen and sedimentological data for Agua Caliente, a freshwater lagoon located in southern Belize, and infer a late Holocene record of human land-use/climate interactions for the nearby prehistoric Maya center of Uxbenká. Land-use activities spanning the initial clearance of forests for agriculture through the drought-linked Maya collapse and continuing into the historic recolonization of the region are all reflected in the record. Human land alteration in association with swidden agriculture is evident early in the record during the Middle Preclassic starting ca. 2600 cal yr BP. Fire slowly tapered off during the Late and Terminal Classic, consistent with the gradual political demise and depopulation of the Uxbenká polity sometime between ca. 1150 and 950 cal yr BP, during a period of multiple droughts evident in a nearby speleothem record. Fire activity was at its lowest during the Maya Postclassic ca. 950–430 cal yr BP, but rose consistent with increasing recolonization of the region between ca. 430 cal yr BP and present. These data suggest that this environmental record provides both a proxy for 2800 years of cultural change, including colonization, growth, decline, and reorganization of regional populations, and an independent confirmation of recent paleoclimate reconstructions from the same region.
    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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    Towards Organic Carbon Isotope Records from Stalagmites: Coupled δ13C and 14C Analysis Using Wet Chemical Oxidation (2019)
    Cambridge University Press
    Details
    Publication Date: 2019-04-23
    Description: Speleothem organic matter can be a powerful tracer for past environmental conditions and karst processes. Carbon isotope measurements (δ13C and 14C) in particular can provide crucial information on the provenance and age of speleothem organic matter, but are challenging due to low concentrations of organic matter in stalagmites. Here, we present a method development study on extraction and isotopic characterization of speleothem organic matter using a rapid procedure with low laboratory contamination risk. An extensive blank assessment allowed us to quantify possible sources of contamination through the entire method. Although blank contamination is consistently low (1.7 ± 0.34 – 4.3 ± 0.86 μg C for the entire procedure), incomplete sample decarbonation poses a still unresolved problem of the method, but can be detected when considering both δ13C and 14C values. We test the method on five stalagmites, showing reproducible results on samples as small as 7 μg C for δ13C and 20 μg C for 14C. Furthermore, we find consistently lower non-purgeable organic carbon (NPOC) 14C values compared to the carbonate 14C over the bomb spike interval in two stalagmites from Yok Balum Cave, Belize, suggesting overprint of a pre-aged or even fossil source of carbon on the organic fraction incorporated by these stalagmites.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Published by Cambridge University Press
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  • 3
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    The Granite Problem: Evidence from the Quartz and Feldspar of a Tertiary Granite (1954)
    Cambridge University Press
    Details
    Publication Date: 1954-02-01
    Description: The inversion temperatures of the quartz from twenty-five specimens of the Beinn an Dubhaich granite have been measured and found to correspond to the inversion temperatures of quartz from rhyolites previously studied. Optical and X-ray studies of the alkali and plagioclase feldspars indicate high temperature modifications. The Beinn an Dubhaich granite has the textural and compositional features of a granite together with mineralogical features normally associated with rhyolitic rocks. The results serve to emphasize that methods are now available which make it possible in some cases to determine whether a particular granite was formed by metamorphism of sediments or by crystallization of a magma. It is concluded that the older granites and those which crystallized at greater depths probably have undergone considerable rearrangement of their mineralogical and textural features subsequent to primary crystallization.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 4
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    Simulations of the 1979–88 polar climates by global climate models (1995)
    Cambridge University Press
    Details
    Publication Date: 1995-01-01
    Description: The simulation of the northern and southern polar climates for 1979–88 by 14 global climate models (GCMs), using the observed monthly averaged sea-surface temperatures and sea-ice extents as boundary conditions, is part of an international effort to determine the systematic errors of atmospheric models under realistic conditions, the so-called Atmospheric Model Intercomparison Project (AMIP), In this study, intercomparison of the models’ simulation of polar climate is discussed in terms of selected surface and vertically integrated monthly averaged quantities, such as sea-level pressure, cloudiness, precipitable water, precipitation and evaporation/sublimation. The results suggest that the accuracy of model-simulated climate features in high latitudes primarily depends on the horizontal resolution and the treatment of physical processes in the GCMs. AMIP offers an unprecedented opportunity for the comprehensive evaluation and validation of current atmospheric models and provides valuable information for model improvement.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 5
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    Evaluating moist physics for Antarctic mesoscale simulations (1997)
    Cambridge University Press
    Details
    Publication Date: 1997-01-01
    Description: The performance of an explicit cloud physics parameterization is examined with simulations of high southern latitude winter climate using a version of the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model, version 4. The results reveal that there are three moist physics regimes in the vertical over the elevated interior of Antarctica: the very cold upper troposphere, the relatively warm middle troposphere and the cold boundary layer. Deficiencies for these layers include excessive cloud ice in the upper troposphere, excessive cloud ice in the inversion layer near the ice surface, overly warm temperatures in the lower troposphere, overly cold temperatures in the upper troposphere and excessive downward longwave radiation at the Earth’s surface. Three sensitivity experiments were performed to investigate possible improvements in the cloud parameterization. The results indicate that a reduction of the numerous cloud condensation nuclei, while reducing some errors, appears to be insufficient to improve the simulation. A reduction in the excessive cloud ice in the upper troposphere significantly improves the simulation of upper-tropospheric temperature.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 6
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    Global atmospheric responses to Antarctic forcing (1998)
    Cambridge University Press
    Details
    Publication Date: 1998-01-01
    Description: To evaluate the greatest impact that sea-ice anomalies around Antarctica could have on the global atmosphere, 15 year seasonal cycle simulations are conducted with the U.S. National Center for Atmospheric Research Community Climate Model version 2.1. Sensitivity simulations are performed with the following conditions: (1) all sea ice in the Southern Hemisphere is replaced by year-round open water, but the permanent ice shelves are retained (NSIS); and (2) all sea ice in the Southern Hemisphere and the major ice shelves are removed and replaced by open water (NISH). The results are compared to a standard run (CNT) with boundary conditions set for the present climate. The comparison shows that trains of positive and negative anomalies in zonal-mean fields extend into the tropical latitudes of the Northern Hemisphere. Anomalies are largest during April-October. The additional removal of the ice shelves in NISH enhances the response, as zonally averaged anomalies are similar in pattern to those in NSIS but are roughly twice as large poleward of 50° S, and only slightly larger farther north. Anomalies in the eddy fields are found in both hemispheres. in NISH, and to a lesser degree in NSIS. these anomalies appear to be related to a delayed northern advance over China during June of the rain front associated with the summer monsoon. Consequently, precipitation is enhanced in middle and southern China and decreased in northern China. Observational analyses have also found links between Antarctic sea-ice variations and modulations of the East Asian monsoon.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 7
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    Evaluating moist physics for Antarctic mesoscale simulations (1997)
    Cambridge University Press
    Details
    Publication Date: 1997-01-01
    Description: The performance of an explicit cloud physics parameterization is examined with simulations of high southern latitude winter climate using a version of the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model, version 4. The results reveal that there are three moist physics regimes in the vertical over the elevated interior of Antarctica: the very cold upper troposphere, the relatively warm middle troposphere and the cold boundary layer. Deficiencies for these layers include excessive cloud ice in the upper troposphere, excessive cloud ice in the inversion layer near the ice surface, overly warm temperatures in the lower troposphere, overly cold temperatures in the upper troposphere and excessive downward longwave radiation at the Earth’s surface. Three sensitivity experiments were performed to investigate possible improvements in the cloud parameterization. The results indicate that a reduction of the numerous cloud condensation nuclei, while reducing some errors, appears to be insufficient to improve the simulation. A reduction in the excessive cloud ice in the upper troposphere significantly improves the simulation of upper-tropospheric temperature.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 8
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    Spatial and morphological change on Eliot Glacier, Mount Hood, Oregon, USA (2007)
    Cambridge University Press
    Details
    Publication Date: 2007-01-01
    Description: Eliot Glacier is a small (1.6 km2) glacier on Mount Hood, Oregon, USA, and its ablation zone is largely covered with rock debris. We examine the interrelated processes of ablation rates, ice thickness and surface velocities to understand the retreat rate of this glacier. Since measurements began in 1901, the glacier has retreated 680 m, lost 19% of its area and thinned by about 50 m at the lower glacier profile before the terminus retreated past that point. The upper profile, 800m up-glacier, has shown thinning and thickening due to a kinematic wave resulting from a cool period during the 1940s–70s, and is currently about the same thickness as in 1940. Overall, the glacier has retreated at a slower rate than other glaciers on Mount Hood. We hypothesize that the rock debris covering the ablation zone reduces Eliot Glacier’s sensitivity to global warming and slows its retreat rate compared to other glaciers on Mount Hood. Spatial variations in debris thickness are the primary factor in controlling spatial variations in melt. A continuity model of debris thickness shows the rate of debris thickening down-glacier is roughly constant and is a result of the compensating effects of strain thickening and debris melt-out from the ice.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 9
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    Simulations of the 1979–88 polar climates by global climate models (1995)
    Cambridge University Press
    Details
    Publication Date: 1995-01-01
    Description: The simulation of the northern and southern polar climates for 1979–88 by 14 global climate models (GCMs), using the observed monthly averaged sea-surface temperatures and sea-ice extents as boundary conditions, is part of an international effort to determine the systematic errors of atmospheric models under realistic conditions, the so-called Atmospheric Model Intercomparison Project (AMIP), In this study, intercomparison of the models’ simulation of polar climate is discussed in terms of selected surface and vertically integrated monthly averaged quantities, such as sea-level pressure, cloudiness, precipitable water, precipitation and evaporation/sublimation. The results suggest that the accuracy of model-simulated climate features in high latitudes primarily depends on the horizontal resolution and the treatment of physical processes in the GCMs. AMIP offers an unprecedented opportunity for the comprehensive evaluation and validation of current atmospheric models and provides valuable information for model improvement.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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