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1.
Combining cosmogenic nuclides and major elements from moraine soil profiles to improve weathering rate estimates 总被引：1，自引：0，他引：1
Previous studies of chemical weathering rates for soil developed on glacial moraines generally assumed little or no physical erosion of the soil surface. In this study, we investigate the influence of physical erosion on soil profile weathering rate calculations. The calculation of chemical weathering rates is based on the assumption that soil profiles represent the integrated amount of weathering since the time of moraine deposition. The weathering rate of a surface subjected to denudation is the sum of the weathering loss from the existing soil profile added to the weathering loss in the material removed by denudation, divided by the deposition age. In this study, the amount of weathered material removed since moraine deposition is calculated using the denudation rate estimated from cosmogenic nuclide data and the deposition age of the moraine. Weathering rates accounting for denudation since moraine deposition are compared to weathering rates based on the assumption of no physical erosion and on the assumption of steady-state denudation for the Type Pinedale moraine ( 21 ka) and the Bull Lake-age moraine ( 140 ka) in the Fremont Lake Area (Wind River Mountains, Wyoming, USA). The total weathering rates accounting for denudation are 8.15 ± 1.05 g(oxide) m− 2 y− 1 for the Type Pinedale moraine and 4.78 ± 0.89 g(oxide) m− 2 y− 1 for the Bull Lake-age moraine, which are 2 to 4 times higher, respectively, than weathering rates based on the assumption of no physical erosion. The weathering rates based on denudation since moraine deposition are comparable or smaller than weathering rates assuming steady-state denudation. We find the assumption of steady-state denudation is not valid in depositional landscapes with young deposition ages or slow denudation rates. The decrease in weathering rates over time between the Type Pinedale and Bull Lake-age soils that is observed in the case of no physical erosion is decreased when the influence of denudation on the total weathering rates is taken into account. Fresh unweathered material with high reactive mineral surface area is continuously provided to the surface layer by denudation diminishing the effect of decreasing weathering rate over time. 相似文献
2.
BY TIMOTHY F. JOHNSEN HELENA ALEXANDERSON DEREK FABEL STEWART P.H.T. FREEMAN 《Geografiska Annaler: Series A, Physical Geography》2009,91(2):113-120
The overall pattern of deglaciation of the southern part of the Scandinavian Ice Sheet has been considered established, although details of the chronology and ice sheet dynamics are less well known. Even less is known for the south Swedish Upland because the area was deglaciated mostly by stagnation. Within this area lies the conspicuous Vimmerby moraine, for which we have used the terrestrial cosmogenic nuclide (10 Be) exposure dating technique to derive the exposure age of six glacially transported boulders. The six 10 Be cosmogenic ages are internally consistent, ranging from 14.9 ± 1.5 to 12.4 ± 1.3 ka with a mean of 13.6 ±0.9 ka. Adjusting for the effects of surface erosion, snow burial and glacio-isostatic rebound causes the mean age to increase only by c. 6% to c. 14.4± 0.9 ka. The 10 Be derived age for the Vimmerby moraine is in agreement with previous estimates forthe timing of deglaciation based on radiocarbon dating and varve chronology. This result shows promise for further terrestrial cosmogenic nuclide exposure studies in southern Sweden. 相似文献
3.
"三元剥蚀"与路南石林发育 总被引：3，自引：0，他引：3
石林是一种稀有的喀斯特地貌景观,其发育演化有其独特的过程。本文提出了石林发育的"三元剥蚀"机制,通过对土下溶蚀速率、表土剥蚀速率与(石)柱顶剥蚀速率三者不同组合的分析,讨论了石林发育的方向与趋势,并对当前路南石林发育的阶段和方向进行了具体研究。研究表明,作为石林增长拔高源动力的土下溶蚀强度的影响范围是有限的,其下限约在土下10m处,而真正能促使石林快速发育的深度是在土下2m以内。在现代自然条件下,路南石林顶部的剥蚀降低速度为10.4mm/ka,土下的溶蚀加深速度为26.17 mm/ka,石林的实际高度仍以15.77mm/ka的速度在拔高;表土剥蚀速度为650mm/ka,石林的可见高度现正以639.6mm/ka的速度增加,土壤正以623.83mm/ka的速度快速变薄,表明虽然目前石林的可见高度仍在增加,但其发育的最佳时期已经过去。 相似文献
4.
Richard A. Shakesby John A. Matthews Mark S. Berrisford & Lindsey J. McEwen 《Geografiska Annaler: Series A, Physical Geography》1999,81(1):31-45
It is demonstrated that pronival (protalus) ramparts can be formed by a snow-push mechanism and need not accumulate in the conventional manner as a result of supranival processes. Ridges in pronival positions up to 1.2 m high and of unequivocal snow-push origin are described from two sites in Smørbotn cirque, Romsdalsalpane, southern Norway. The seven lines of evidence are: (1) parallel abrasion tracks on large boulders embedded in the substrate; (2) displaced surface and embedded clasts with proximal furrows; (3) corrugated (flute-like) substrate surfaces; (4) the sickle-shaped plan-form of the ridges; (5) generally asymmetrical ridge cross-profiles (shallow, concave proximal; steep, convex distal); (6) strong preferred orientations and dips of surface-embedded clasts on ridge proximal slopes; and (7) a subnival/pronival ridge comprising loosely packed diamicton forming along the contact zone between the snowbed and substrate. This evidence indicates ridge formation by snow sliding involving bulldozing of the substrate. Factors considered important in favouring snow push producing distinct pronival ramparts at the sites include: a maritime periglacial climate with heavy winter snowfall and rapid snow-firn conversion producing snow densities of up to 900 kg m–3 ; a deformable substrate with relatively small inputs of rockfall or avalanche debris; and a steep headwall susceptible to snow avalanching and hence enhanced snow supply. Consideration is given to the prospect that larger pronival ramparts can form incrementally by a snow-push mechanism. 相似文献
5.
JAMES BOCKHEIM 《Geografiska Annaler: Series A, Physical Geography》2007,89(3):153-165
Soil‐forming processes and soil development rates are compared and contrasted on glacial deposits in two adjacent and coeval valleys of the Quartermain Mountains, which are important because they display Miocene glacial Stratigraphy and some of the oldest landforms in the McMurdo Dry Valleys. More than 100 soil profiles were examined on seven drift sheets ranging from 115 000 to greater than 11.3 million years in age in Beacon Valley and Arena Valley. Although the two valleys contain drifts of similar age, they differ markedly in ice content of the substrate. Whereas Arena Valley generally has ‘dry‐frozen’ permafrost in the upper 1 m and minimal patterned ground, Beacon Valley contains massive ice buried by glacial drift and ice cored rock glaciers and has ice‐cemented perma‐frost in the upper 1 m and considerable associated patterned ground. Arena Valley soils have twice the rate of profile salt accumulation than Beacon Valley soils, because of lower available soil water and minimal cryoturbation. The following soil properties increase with age in both valleys: weathering stage, morphogenetic salt stage, thickness of the salt pan, the quantity of profile salts, electrical conductivity of the horizon of maximum salt enrichment, and depth of staining. Whereas soils less than 200 000 years and older soils derived from sandstone‐rich ground moraine are Typic Anhyorthels and Anhyturbels, soils of early Quaternary and older age, particularly on dolerite‐rich drifts, are Petronitric Anhyorthels. Arena Valley has the highest pedodiversity recorded in the McMurdo Dry Valleys. The soils of the Quartermain Mountains are the only soils in the McMurdo Dry Valleys known to contain abundant nitrates. 相似文献
6.
《Geomorphology》1988,1(2):143-160
A soil chronosequence was examined on landslide scars of different ages in the Taranaki hill country. This area, underlain by Tertiary silty sandstone, was deforested 90 years ago. Sequential aerial photographs, historical terrestrial photographs and documented erosion events were used to date landslide scars formed since forest removal and establish age control for the chronosequence.Soil depth increased with landslide age and was used as an index of soil formation. Mean soil depth increased from 5 cm on 15 year old scars to 20 cm on 82 year old scars. Measures soil depths were attributed to rafted soil, colluvium and bedrock weathering. A chronofunction was derived by regressing mean soil depth against the logarithm of known scar age. Similarly, a second chronofunction was derived by excluding depths of rafted soil from the calculation of mean soil depth to describe soil accumulation on exposed bedrock within the landslide scar. This chronofunction showed a better correlation (r2 = 0.92 compared with r2 = 0.79) and can give an estimate of the age of other landslide scars to within ±27% for ages up to 90 years.The rate of soil depth increase averaged 3.5 mm yr−1 over the first 40 years after slipping but dropped to 1.2 mm yr−1 over the following 50 years. The logarithmic chronofunction suggests that the rate of soil formation further decreases beyond 90 years. Soil formation is primarily a result of bedrock weathering and accumulation of colluvium derived from surface fragmentation of exposed bedrock and crumbling scar margins. 相似文献
7.
新疆阿尔泰山东段冰碛物光释光测年研究 总被引：3，自引：0，他引：3
冰川是塑造地表形态最积极的外营力之一,对冰川地貌的年代学研究是重建古冰川发展史的关键,也是研究气候变化的重要途径。冰碛物是冰川作用的直接产物,代表过去发生的冰川事件,对冰碛物进行准确测年能够为重建古冰川的进退、理解区域古气候变化提供年代学支撑。本文在新疆阿尔泰山东段采集了8个冰碛物样品以进行光释光测年,利用单片再生剂量法对90~125 μm的石英颗粒进行等效剂量的测定。通过等效剂量值频率分布特征及De（t）坪区图分析得出大部分冰碛物的光释光信号晒退不彻底,所以利用一阶动力学公式对持续激发的光释光信号晒退曲线（CW-OSL）进行多组分拟合拆分,得到快速、中速、慢速3种组分,依据分离出的快速组分确定等效剂量值。研究结果显示,距今32 ka以来阿尔泰山东段区域在MIS3阶段、MIS2阶段、8.2 ka左右、全新世大暖期及新冰期等5个时段有冰川发育,冰川发育与气候变化密切相关。 相似文献
8.
《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(4):290-302
Two-years of ground temperatures (10 cm and 50 cm depths) from the foreland of Storbreen in the Jotunheimen Mountains of Norway demonstrate that seasonal and annual ground temperature differences induced by microtopographic position at a constant elevation are comparable to differences stemming from ～ 100 m to ～ 300 m in elevation. Between ～ 1460 m a.s.l. and ～ 1150 m a.s.l., mean annual lapse rates calculated for soil depths of 10 cm were≤0.8°C per100m beneath tundra, moraine crests, and moraine proximal base positions, each of which was calculated independently. Seasonal lapse rates were often larger,≥1.0°C per 100m in both summer and winter. The calculated ground temperature lapse rates compare favorably with those already reported in the literature for the region. Categorical data in the form of Thawed, Freeze-Thaw, Isothermal, and Frozen Days also showed considerable variability by elevation and microtopographic position. Variability in growing conditions was examined by calculating Thawing Degree Days and Growing Degree Days. These values sometimes, but not always, mimic ground temperature patterns. Although no wintertime field observations are available, the depth and duration of seasonal snow cover appears to be the primary source of variability. 相似文献
9.
Kråkenes faces the open sea on the west coast of Norway. During the Younger Dryas a cirque glacier deposited a large outer and a smaller inner moraine in a cirque at the site and melt-water entered a small lake depositing glaciolacustrine sediments. The glaciolacustrine succession can be divided into three sub-units corresponding to the advance, the still-stand and the retreat phases of the glacier. The sediment succession contains both varves and other types of rhythmites, the latter being mainly deposited as turbidity underflows caused by localized slumping events. Lee-side accumulation of snow by wind and avalanching into the cirque was crucial to form and maintain the cirque glacier once summer temperatures were low enough. At maximum, the glacier likely was in equilibrium with climate. The initial retreat from the maximum position might have been triggered by fall-out of volcanic ash from Iceland, but the continued retreat was due to increased ablation season temperatures. The most rapid change in climate at the Younger Dryas/Preboreal transition occurred after the cirque glacier had melted away completely. 相似文献
10.
Robert G. Darmody & Colin E. Thorn 《Geografiska Annaler: Series A, Physical Geography》1997,79(4):215-222
Chemical weathering and associated soil development trends on glacial forelands are commonly assumed to exhibit increases with time elapsed since glaciation. However, this gross trend is complicated by several other factors including elevation, aspect, and microtopography. This paper demonstrates that on the glacial foreland at Storbreen, Jotunheimen, Norway, chemical weathering and associated soil development trends show significant elevational influences. We sampled soils at shallow depths (0–1, 1–5, and 15–20 cm) at two sites on a moraine dated to 1750 at its elevational extremes of 1155 m (site L) and 1385 m (site H). The two moraine sites also differed developmentally from an adjacent 9000-year-old surface (site T) at an intermediate elevation, 1205 m. Analyses were conducted on the fine-earth fractions. Extractable elemental composition exhibited detectable differences between the same-age soils at different elevations with the lower site L tending to have measured parameters intermediate between the high site H and the older site T. Weathering, as indicated by mineralogy, was more pronounced at the 9000-year-old site T and least evident at the high elevation site H. In addition, elevation under the conditions of the field research may inhibit pedogenesis as indicated by the chemical data. Site H, for example, showed little variation with depth and had in general, less organic matter accumulation, smaller C:N ratio, greater pH, and lesser amounts of the measured extractable elements than the soil at site L. Site T generally had smaller pH and larger levels of the measured elements than the other sites. It was concluded that elevation has a significant control on weathering and pedogenesis that may mask the effects of age in this cold and wet environment. 相似文献
11.
ABSTRACTThis study investigated the late Quaternary climate and environmental characteristics of two tributary valleys (Xingmu and Depu Valleys) in the Parlung Zangbo Valley, southeastern Tibetan Plateau. Optically stimulated luminescence (OSL) samples collected from moraines at the mouth of Xingmu Valley produce a wide age range from 13.9 ka to 76 ka. The ages measured from the lenticular sand are consistent with the relative geomorphic sequence of the landforms. Lenticular sand layers below the moraine were dated to 37.9 ka and 44.7 ka, indicating that fluvial processes were likely dominant in the valley during Marine Isotope Stage (MIS) 3. The outer moraine ridges at the valley mouth were formed during 13.9 ka and 26.5 ka, corresponding to MIS2. At Depu Valley, OSL samples from two sets of lateral and terminal moraines close to the modern glacier, provide ages from 1.4 ka to 29.2 ka. The paleosol layer widely developed during 2.6 cal ka BP and 8.7 cal ka BP in the study area, reflecting a relatively warm condition during the mid-Holocene. 相似文献
12.
沙障在固定流沙、促进植被恢复和改良土壤等生态建设方面起着重要作用。对毛乌素沙地设置沙柳（Salix psammophila）沙障6、8、10、11、12年的沙丘迎风坡（裸露沙丘地作为对照）开展了植被调查和土壤养分测试分析。结果显示：设障8年后的沙丘迎风坡0—30 cm深度内的土壤有机质、全氮含量显著（P<0.05）高于流动沙丘,且设障10—11年沙丘迎风坡植被盖度、0—80 cm深度内土壤有机质和全氮含量达到最大,但全磷和全钾含量无明显的变化,所有样地间和3个深度层间的全磷、全钾含量均无显著性差异;植被总盖度、0—80 cm深度内土壤有机质含量及全氮含量相互之间存在极显著线性正相关关系（P<0.01）,而且土壤pH值随有机质含量增加而线性降低。沙柳沙障固沙地的植被盖度、土壤有机质和全氮相互之间存在趋同性,且布设10年的沙障土壤改良和植被恢复成效达到最大,之后表现出下降趋势。据此建议活体沙柳沙障在维持其固沙功效的前提下以10年为限需进行平茬处理。 相似文献
13.
14.
Moraine Exposure Dates Imply Synchronous Younger Dryas Glacier Advances in the European Alps and in the Southern Alps of New Zealand 总被引：6，自引：0，他引：6
Susan Ivy-Ochs Christian Schlüchter Peter W. Kubik & George H. Denton 《Geografiska Annaler: Series A, Physical Geography》1999,81(2):313-323
Samples taken from the top surfaces of boulders on the Lake Misery moraines at Arthur's Pass, in the Southern Alps of New Zealand, were analysed for 10 Be by accelerator mass spectrometry. Exposure ages calculated with the currently accepted production rate, along with scaling corrections for sample latitude and elevation (42°50'S, 960 m), are: 9300 ± 990, 11,000 ± 1360, 11,410 ± 1030, 12,050 ± 960, and 12,410 ± 1180 years. We consider the date of 9300 years to be an outlier, not included in our mean exposure age of 11,720 ± 320 years for the Lake Misery moraines. Based on exposure ages and geomorphologic similarities, we compare the Lake Misery moraines with an Egesen moraine complex at Julier Pass in the Swiss Alps (46°30'N, 2200 m). Based on the 10 Be, 26 Al, and 36 Cl exposure ages of three boulders, we calculate a mean exposure age of 11,750 ± 140 years for the outer Egesen moraine at Julier Pass. Based solely on 10 Be measurements, we obtain a mean exposure age of 11,860 ± 210 years for this outer moraine. Egesen moraines in the Swiss Alps represent glacier readvance during the Younger Dryas cold reversal, based on regional correlations and on basal radiocarbon dates from bogs located up-valley of Egesen moraines. The exposure dates from Arthur's Pass and Julier Pass show synchronous glacier advances both in the Southern Alps and in the European Alps during the European Younger Dryas chronozone of Mangerud et al . 相似文献
15.
以烟台市的芝罘岛风砂沉积剖面为研究对象,分析色度特征,并结合光释光测年探讨末次间冰期该地区的气候。结果表明：1）色度参数L*均值为52.13,在整个剖面表现为黄土层L*高于古土壤层,指示寒冷干燥的气候条件。a*、b*、C*、h*均值依次为11.18、25.03、27.43和0.421,其值均表现为古土壤层高于黄土层,指示温暖湿润的气候条件。2）各色度参数在剖面垂直方向上呈现峰谷交替的3个旋回,反映该地区末次间冰期的气候变化经历由夏季风占主导,气候暖湿,降水较多（MIS5e：118.5—124.9 ka）→夏季风势力减弱,冬季风增强,气温下降（MIS5d：105.2—118.5 ka）→夏季风影响明显,气候湿热（MIS5c：94.7—105.2 ka）→冬季风增强,气温下降（MIS5b：83.4—94.7 ka）→开始转向暖湿（MIS5a：70.18—83.4 ka）→再转向干冷（MIS4：62.85—70.18 ka）的冷暖震荡。 相似文献
16.
1990~2000年中国土壤碳氮蓄积量与土地利用变化 总被引：52，自引：1，他引：51
基于2473个土壤剖面资料和1980年代末~1990年代末陆地卫星TM影像分析中国1990~2000年林地、草地、耕地之间的土地利用变化对土壤碳氮蓄积量的影响。IPCC建议的国家温室气体清单方法计算表明从1990~2000年中国林地、草地、耕地土壤 (30 cm) 有机碳氮库分别损失了77.6±35.2 TgC (1Tg = 106 t) 和5.6±2.6 TgN,年均损失约7.76 TgC/yr和0.56 TgN/yr,其中耕地土壤碳库分别增加了79.0±7.7 TgC 和9.0±0.7 TgN,草地土壤碳氮蓄积量分别损失了100.7±25.9 TgC和9.8±2.2 TgN,林地土壤碳氮蓄积量分别损失了55.9±17.0 TgC和4.9±1.1 TgN。同时根据中国6大行政区林地、耕地和草地之间的相互转换面积、土壤有机碳氮密度的变化率进行估算,表明土壤 (30 cm和100 cm) 有机碳氮蓄积量分别损失了53.7 TgC、5.1 TgN和99.5 TgC 、9.4 TgN。由于中国不同地区土地利用变化的空间格局差异显著,从而导致东北地区土壤碳氮蓄积量变化较大,而华东地区变化较小。 相似文献
17.
黄土不同指标的古环境意义探讨 总被引：8，自引：5，他引：3
在确认“黄土也是古土壤”的前提下,对新近发现的位于黄土高原西北部沙漠黄土边界带的彭阳剖面进行了烧失量、色度、磁化率、粒度、CaCO3等环境变化代用指标的系统测试。通过建立土壤发育指数和红化指数,探讨了各指标与古土壤发育强度之间的关系。根据古土壤的发育强度,初步建立了800 ka BP生态脆弱区的高分辨率环境图谱。此图谱与公认的海洋氧同位素曲线、洛川剖面可以进行良好的对比,并揭示出更多的环境变化信息。 相似文献
18.
甘肃黄土高原土壤水分变化对冬小麦产量的影响 总被引：1，自引：0，他引：1
甘肃黄土高原属半干旱和半湿润气候过渡区。潜在蒸散量大于降水量,土壤水是影响冬小麦生产最直接因素。运用甘肃西峰农业气象试验站1981-2010 年冬小麦大田试验及土壤湿度观测资料,对近30 年土壤水变化规律及与冬小麦各产量要素的关系进行分析。结果表明,冬小麦贮水量最大时段为冬前生长期,其次为返青期至拔节期,最小为孕穗期至成熟期。耗水量最大时段为孕穗期至成熟期,其次为冬前生长阶段,最小为返青期至拔节期。1981-2010年土壤100 cm土层、1990-2010 年200 cm土层贮水量呈减少趋势,耗水量呈增加趋势。冬小麦土壤水分利用率呈上升趋势,变化转折点出现在1998 年。200 cm、100 cm土层贮水量与冬小麦不孕小穗率相关性显著。不同生长阶段各层次土壤贮水量均与千粒重相关性显著,且随着深度加深,相关性愈加显著。冬前生长阶段、返青期至拔节期各深度层次土壤贮水量与单株成穗数相关性分别通过0.1、0.01 信度水平检验。在冬小麦各生长阶段,各层次土壤贮水量与单产相关性显著。5 月中旬100 cm 土层贮水量对产量影响较大,aj(t) 值达20 kg/hm2·mm。不孕小穗率与不同生长阶段100 cm土层耗水量均呈显著负相关关系。千粒重与冬前生长阶段的各深度层次耗水量相关性显著。单株成穗数与返青期至拔节期上层土壤耗水量相关性显著。单产与孕穗期至成熟期各层次耗水量相关性显著。从当年9 月到次年5 月100 cm土层耗水量对单产影响逐渐增大,5 月中旬aj(t) 达25 kg/hm2·mm。此后耗水量对产量的影响逐渐降低。 相似文献
19.
根据27个土壤剖面的405个土壤样品,研究云南中部地区华山松林、旱冬瓜林、云南松林的土壤含水率、容重和细根重及其垂直分布特征。结果表明：3种森林100em深土壤的平均含水率分别是（28．79±11．98）％、（24．66±9．89）％、（14．11±5．84）％,差异极显著;平均容重分别是（1．14±0．20）g／cm3、（1．26±0．18）g/cm3、（1．42±0．12）g／cm3,差异极显著;平均细根重分别为（0．1956±0．2144）g／100cm3、（0．0706±0．1066）g／100cm3、（0．1381±0．2989）g／100cm3,在0．05水平上差异显著。华山松林林下土壤的物理性质最好,旱冬瓜林次之,云南松林最差。3种森林里,随着土壤深度增加,土壤含水率增加,土壤容重和土壤细根重减少。华山松林与云南松林平均容重与平均细根重均显著负相关,旱冬瓜林平均含水率与平均容重显著负相关。华山松林下土壤细根量最大,0～20cm层根系占根系总重量的83％。 相似文献
20.
民勤绿洲外围不同林龄人工梭梭林的土壤水分特征 总被引：5，自引：0，他引：5
2009年6月到9月,每月中旬在民勤绿洲边缘不同林龄(2 a,5 a,10 a,20 a,30 a)的人工梭梭林内测试不同深度(20 cm,30 cm,50 cm,100 cm,150 cm和200 cm)的土壤含水量变化情况。分析结果表明,不同林龄的梭梭林内土壤含水量与时间和深度有关。土壤表层含水量主要受自然降雨控制,8月底发生比较大的自然降雨后,9月不同林龄梭梭林内20 cm和30 cm的含水量显著高于其他3个月。土壤50 cm以下的含水量比较稳定,当降雨少,土壤表层含水量低时,可以作为梭梭利用的水分来源。在7月和8月,5 a梭梭林内土壤含水量最低,表明梭梭对土壤水分的消耗最多,栽植密度过大,因此,需要间伐减少植株数量才能维持其稳定性。 相似文献