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Glacial Geomorphology of Bonney Drift, Taylor Valley, Antarctica 总被引：1，自引：0，他引：1
S.M. Higgins George H. Denton & Chris H. Hendy 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):365-389
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In two of the perennially ice-covered lakes in the McMurdo Dry Valleys, lakes Hoare and Bonney in the Taylor Valley, bottom water has 14C ages of 2.7 ka and 10 ka (respectively), rendering 14C ages of bottom sediments highly problematic. Consequently, we tested the effectiveness of thermoluminescence (TL) zeroing in polymineral fine silt material from several depositional environments around and on the lake (stream suspensions, ice-surface sand dune, and silty sand from near the top of the more-than-3m-thick ice). We also conducted TL and infrared-stimulated-luminescence (IRSL) dating tests on material from three box cores recovered from the bottom of Lake Hoare, in a transect away from the abutting Canada Glacier. We observed effective zeroing of light-sensitive TL in suspended silt from one input stream and less effective zeroing from another stream. We observed effective zeroing of light-sensitive TL also in silt from a glacier-proximal eolian ice-surface dune and from sand from within the upper 5 cm of ice. In contrast, in box-core 1, the bottom sediment yielded minimum TL apparent ages of 1500-2600 yrs, with no discernable stratigraphic depth trend. IRSL dating applied to the same box-core samples produced significantly lower age estimates, ranging from ~600 ± 200 yrs to 1440 ± 270 yrs top-to-bottom, an improvement over the depth-constant ~2200 yrs TL ages. In two other cores closer to the Canada Glacier, IRSL ages from ~600 ± 200 yrs (top) to ~ 2900± 300 yrs (at depth) were measured. Not only are the IRSL ages a significant improvement over the TL results, but the near-core-top IRSL ages are also a dramatic improvement over the 14C results (~2.7 ka). IRSL dating has a demonstrated potential to supplant 14C dating for such antarctic lacustrine deposits. 相似文献
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An area north of Lake Fryxell in the Taylor Valley, Antarctica, was surveyed to determine the frequency of occurrence of rocks that show strong evidence of wind abrasion and ventifaction, which is defined here as rocks having well-developed faceting, to define their relative abundance in this area of the ice-free McMurdo Dry Valley system and to provide an indication of the role of wind as a geomorphic agent in this area. The orientation of abrasion-caused features (facets, keels, and grooves) with respect to the present day wind regime is also described. Rocks were examined on five linear transects ranging from 300 to 510 m in length. A total of 1324 rocks were examined. On average, 60% of all rocks exhibited distinct wind abrasion features with polish being the most common feature and polished rocks were distributed equally between survey lines, suggesting abrasion was ubiquitous in the study area. Approximately 4% of the rocks had distinct facets and/or keels, and fine-grained ultramafic peridotite-type rocks produced the most finely-featured forms (i.e., sharp facet edges and keels). A larger percentage, ≈ 12.5%, had grooves. Grooves were typically associated with a tabular form of mafic diabase-type igneous rock. The distribution of faceted ventifacts and grooved rocks was not uniform for the five transects, suggesting that the distribution mechanism for the surface rocks and the source areas determined, to a large extent, what form of ventifact could be produced at a location. The orientation of the grooves and dip directions of the facets indicates the direction of the abrasive winds had a strong westerly component, which coincides with the modern wind regime of winter katabatic flows that move down valley toward the Ross Sea. The orientation of the facets and grooves suggests that the rate of formation of the ventifacts proceeds at a pace greater than other surficial processes (e.g., down-slope soil movement, cryoturbation), which should tend to remove trends in the facet and groove orientations, or that the down-slope movement of the surface is approximately perpendicular to the wind allowing preservation of the alignment. 相似文献
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Matthew A. Konfirst Charlotte Sjunneskog Reed P. Scherer Peter T. Doran 《Journal of Paleolimnology》2011,46(2):257-272
We present a diatom record from a sediment core taken in Lake Fryxell, Taylor Valley, Antarctica. Six zones were defined using
diatom assemblage changes that indicate varying limnological conditions. The early lake stage, ca. 35,000 cal years BP, is characterized by Mayamea atomus f. permitis, a species rarely reported in modern Antarctic Dry Valley environments. An extended period from ca. 35,000 to 19,000 cal years BP is characterized by low diatom abundance, with dominant taxa Luticola spp., Muelleria spp., and Diadesmis contenta. The modern assemblage was established ca. 13,000 cal years BP, after two relatively brief transitional stages. One key species
for this recent period, Navicula lineola var. perlepida, is absent in surface sediments and the modern environment, indicating an environmental change within the last several centuries.
The diatom assemblage is compared to modern diatom communities in Dry Valley streams, which provide the most complete information
on diatom distributions in this region. Although precise environmental interpretation of the core is hampered by limited knowledge
of environmental constraints on many of the diatom taxa present in the lake core, the data provide important new insights
into the history of Glacial Lake Washburn. 相似文献
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Keith A. Brugger 《Geomorphology》2006,75(3-4):318
Ice surface topography of a late Pleistocene glacier complex, herein named the Taylor River Glacier Complex (TRGC), was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps. During the last glacial maximum (LGM), the TRGC covered an area of 215 km2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and/or upland ice fields.Equilibrium-line altitudes (ELAs) for the glaciers of the TRGC were estimated using the accumulation-area ratio method, assuming that ratio to be 0.65 ± 0.05. ELAs thus derived ranged from about 3275 to 3400 m, with a mean of 3340 ± 60 m. A degree-day model (DDM) was used to infer the climatic significance of the LGM ELA. With no appreciable differences in precipitation with respect to modern climate, the ELA implies that mean summer temperatures during the LGM were 7.6 °C cooler than today. The DDM was also used to determine the temperatures required to maintain steady-state mass balances for each of the reconstructed glaciers. The required reductions in summer temperature vary little about a mean of 7.1 °C. The sensitivity of these results to slight (± 25%) changes assumed for LGM precipitation are less than ± 0.5 °C. Even under an LGM climate in which precipitation is assumed to be substantially different (± 50%) than the present, mean summer temperatures must be on the order of 7.0 to 8.5 °C lower to depress equilibrium lines to LGM altitudes. The greater sensitivity of the ELA to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation. 相似文献
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Wisconsinan and Holocene Climate History from an Ice Core at Taylor Dome, Western Ross Embayment, Antarctica 总被引：4，自引：0，他引：4
Eric J. Steig David L. Morse Edwin D. Waddington Minze Stuiver Pieter M. Grootes Paul A. Mayewski Mark S. Twickler & Sallie I. Whitlow 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):213-235
Geochemical data and geophysical measurements from a 554-m ice-core from Taylor Dome, East Antarctica, provide the basis for climate reconstruction in the western Ross Embayment through the entire Wisconsinan and Holocene. In comparison with ice cores from central East and West Antarctica, Taylor Dome shows greater variance of temperature, snow accumulation, and aerosol concentrations, reflecting significant variability in atmospheric circulation and air mass moisture content. Extreme aridity during the last glacial maximum at Taylor Dome reflects both colder temperatures and a shift in atmospheric circulation patterns associated with the advance of the Ross Sea ice sheet and accounts for regional alpine glacier retreats and high lake levels in the Dry Valleys. Inferred relationships between spatial accumulation gradients and ice sheet configuration indicate that advance of the Ross Sea ice sheet began in late marine isotope stage 5 or early stage 4. Precise dating of the Taylor Dome core achieved by trace-gas correlation with central Greenland ice cores shows that abrupt deglacial warming at Taylor Dome was near-synchronous with the ∼14.6 ka warming in central Greenland and lags the general warming trend in other Antarctic ice cores by at least 3000 years. Deglacial warming was following by a warm interval and transient cooling between 14.6 and 11.7 ka, synchronous with the Bølling/Allerød warming and Younger Dryas cooling events in central Greenland, and out of phase with the Antarctic Cold Reversal recorded in the Byrd (West Antarctica) ice core. Rapid climate changes during marine isotope stages 4 and 3 at Taylor Dome are similar in character to, and may be in phase with, the Northern Hemisphere stadial–interstadial (Dansgaard–Oeschger) events. Results from Taylor Dome illustrate the importance of obtaining ice cores from multiple Antarctic sites, to provide wide spatial coverage of past climate and ice dynamics. 相似文献
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Kay Anderson 《The Australian geographer》2005,36(3):267-282
This account sets itself against the binarism of physical versus cultural determinism that drives population–environment debate over people's place on the Australian continent. In reading back into colonial times, it evokes ‘our’ unresolved sense of relation to nature on a continent that has pressed awkward buttons since the time the botanist on Cook's Endeavour, Joseph Banks, first mused over the apparent contradiction on the east coast of human presence and uncultivated land. Australia's ‘state of nature’, including its inhabitants, elicited tensions in Anglo-Celtic peoples’ ambiguous relation with nature that have never gone away or been resolved. Indeed, I argue, against the background of what was considered in eighteenth-century Enlightenment thought to be a distinctly human separation from, and capacity to rise above, nature, that the Australian state of nature/native precipitated a crisis in prevailing ideas of ‘the human’. As consternation grew into the nineteenth century about the very capacity of Aboriginal people for improvement, and particularly for cultivation, I argue they challenged the basis upon which the unity of humankind had been assumed in Enlightenment thought. They could not be comprehended, according to the prevailing conception of racial difference, as a mere variety of the human. The radical idea of innate human difference may thus be understood as arising out of this incomprehension, as an attempt to account for the ontologically inexplicable difference of the Australian Aborigine. This lecture's excursion into the origins of ‘race’ is by way of highlighting the uncertainty of the divide between the human and non-human worlds. Imagining an entangled world of living things may help to craft fresh lines of debate about modes of environmental belonging and becoming on this continent that overcome the stale binaries and blind spots of Australia's population–environment debate. 相似文献
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企业研究的时间地理学框架 --兼论泰勒模式的时间地理学解释 总被引：2，自引：0，他引：2
企业空间扩张是公司地理学研究的重要内容。文章引入关注时空坐标系下对个人或群体的连续活动以及所面临的制约条件进行独到分析的时间地理学概念和理论体系，通过“时空棱柱”、“制约”等核心概念扩张性的应用，对企业空间扩张的代表性理论－泰勒模式做出新的诠释，并以此为基础尝试提出企业研究的时间地理学框架，展望了时间地理学在有关企业家研究、创新扩散研究、企业时间管理、企业行为的制约体系等方面的应用前景。 相似文献
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David L. Morse Edwin D. Waddington Hans-Peter Marshall Tomas A. Neumann Eric J. Steig Jack E. Dibb Dale P. Winebrenner & Robert J. Arthern 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):683-694
Accumulation rate measurements on the East Antarctic plateau are challenging due to both spatial and temporal variability. Annual stratigraphy is often not reliably or consistently preserved in the firn, and so accumulation cannot be determined from snow pit stratigraphy. We present a suite of accumulation rate measurements collected over several seasons at Taylor Dome, East Antarctica. We compare net accumulation results from direct burial rate measurements and β -activity firn cores along a 35 km traverse. The two methods are consistent and show that the net accumulation varies from greater than 10 cm a−1 to about 1 cm a−1 (ice equivalent) southwest to northeast across the dome. We map the depth of shallow radar layering to interpolate and extrapolate these point-location measurements and show that considerable variations occur over kilometer scales resulting from subtle surface topography. We also present accumulation rates estimated from concentration of the cosmogenic isotope 10 Be and from activity profiles of 210 Pb. Finally, satellite passive microwave data are used to estimate spatially averaged accumulation rates on the regional to continental scale to provide a context for these local observations. We show that robust mass balance measurements in this environment must rely on spatial and/or temporal averaging. 相似文献
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Brenda L. Hall & George H. Denton 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):305-336
More than 250 radiocarbon dates of lacustrine algae and marine shells afford a chronology for Ross Sea drift in eastern Taylor Valley. Dates of algae that lived in ice-dammed Glacial Lake Washburn show that grounded Ross Sea ice blocked the mouth of Taylor Valley between 8340 and 23,800 14 C yr bp . Ross Sea ice was at its maximum position at the Hjorth Hill moraine between 12,700 and 14,600 14 C yr bp and was within 500m distance of this position as late as 10,794 14 C yr bp . The implication is that the flow line of the Ross Sea ice sheet which extended around northern Ross Island and across McMurdo Sound to Taylor Valley must have remained intact, and hence that a grounded ice sheet must have existed east of Ross Island as late as 8340 14 C yr bp . Evidence from ice-dammed lakes in Taylor Valley and from shells from McMurdo Sound suggests grounding-line retreat from the vicinity of Ross Island between 6500 and 8340 14 C yr bp . If this is correct, then most recession to the present-day grounding line on the Siple Coast took place subsequently in the absence of significant deglacial sea-level rise. Rising sea level may have triggered internal mechanisms within the ice sheet that led to retreat, but did not in itself drive continued ice-sheet recession. Ice retreat, once set in motion, continued in the absence of sea-level forcing. If correct, this hypothesis implies that the grounding line could continue to recede into the interior reservoir of the West Antarctic Ice Sheet. 相似文献
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J.M. Powell 《The Australian geographer》1997,28(1):39-52
This exercise in a type of applied historiography begins by annotating aspects of reform in Western education from the 1880s to the 1930s, an interval which exhibits the responses of ‘new’ subjects to political and social demands for improved civics education, and encompasses the inauguration of a recognisably ‘academic’ geography in Australia. Designedly, since the nominated period also incorporates the early life and career of pioneering geographer Griffith Taylor, the discussion probes beneath the strata of obfuscatory generalisation to relate one individual's engagement with the vortex of change. More specifically, it extracts a few lessons from Taylor's approach to ‘Nation‐Planning’ to suggest an appropriate orientation to current reformism in Australian education. It is argued that, while this trend questions the civic utility of established disciplines, it has been badly served by a disturbing ignorance of the social and intellectual heritage of the subjects under challenge. 相似文献