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91.
The physical characteristics of surface sediments from a suite of pristine lakes on Signy Island, maritime Antarctic, were used to develop a quantitative link between catchment ice-extent and lake-sediment response. Percentage dry weight, median particle size, percentage loss-on-ignition and wet density of the lakes' surface sediments were the most significant variables explaining contemporary catchment ice-extent. Two independent reconstruction models – Partial Least Squares (PLS) and a Modern Analog Technique (MAT) – were applied to dated sediment cores at two sites on Signy Island. The validity of the reconstructions was tested against historical information on catchment ice-extent. With sufficiently high sedimentation rates and sampling resolution, the models can predict sub-decadal changes in ice-extent. The model results are best regarded as indicators of erosion resulting from meltwater activity in the catchment. Comparison of results with Twentieth Century climate records affirms the hypothesis that climatic warming is the most likely cause for the ice retreat observed on Signy Island during the last 40 yrs. Similar reconstruction models using these simple sedimentary measures could be developed for analogous locations in the Antarctic and in Arctic and Alpine regions. 相似文献
92.
青海达布逊湖50万年以来气候变化的孢粉学证据 总被引:18,自引:0,他引:18
基于青海柴达木盆地达布逊湖达 1井岩芯样品孢粉分析结果,将孢粉谱划分为Q2 、Q3 和Q4 三个孢粉带;并根据孢粉组合特征讨论了过去 5 0万年中研究区植被演化和古气候变化问题。达 1井沉积剖面年龄根据古地磁测定。研究结果表明,柴达木盆地中更新世中、晚期 ( 5 0 0~ 130kaBP)气候可能为暖温带半潮湿型,晚更新世 ( 130~ 10kaBP)气候为温带半干燥型,全新世 ( 10~ 0kaBP)气候为寒温带干燥型。晚更新世气候变化与青藏高原古里雅冰芯所记录的冷暖事件演变基本一致. 相似文献
93.
94.
塔里木及邻区晚古生代早期古气候与构造 总被引:2,自引:0,他引:2
影响塔里木及邻区晚古生代早期气候的地球内部因素为古昆仑和南天山两个古洋盆封闭及有关的两条缝合构造带演化,从而形成上述时空段内热带海洋气候、热(亚热)带季风气候、热带沙漠气候以及热带滨岸干湿气候区域的更替,古气候特征的判断主要依据古地磁数据、古生态气候学、沉积环境诸方面。 相似文献
95.
西菲律宾海沉积物稀土元素地球化学 总被引:7,自引:0,他引:7
对取自西菲律宾海区3个沉积物柱样(WP1、WP2和WP40)的32个样品的稀土元素(REE)地球化学行为进行了系统的研究。区内沉积物表现出以下特征:①稀土元素含量及总量(ZREE)较低,WP1、WP2和WP40孔的ΣREE依次为72.91×10-6,54.15×10-6和54.18×10-6,REE在粘土粒级中得到了较大富集;②REE球粒陨石标准化的分布模式曲线表现为负斜率,富集轻稀土,WP1、WP2和WP40孔LREE/HREE比值平均值为37.36,26.33和17.16,页岩标准化曲线大致呈水平;③与球粒陨石和页岩相比,Ce都表现为强烈的亏损;以球粒陨石为标准,WP40孔表现为弱的Eu正异常,其他两孔表现为弱的Eu负异常;以页岩为标准,皆显示Eu正异常;④ΣREE纵向变化曲线与CaCO3旋回曲线有良好的对应关系。上述特征表明:①沉积物的来源复杂,有陆源、火山源、生物源和自生源,在所研究的三个孔中,WP1孔含有较多的陆源物质,WP2和WP40含有较多的火山物质;②被粘土吸附是本区REE重要的存在形式;③沉积物形成环境为氧化条件;④据ΣREE的纵向变化曲线与CaCO3旋回曲线,将本区沉积物自下而上划分为末次冰期亚间冰期沉积、冰期最盛期沉积和全新世沉积。 相似文献
96.
湖相介形虫壳的稳定同位素和微量元素在古气候研究中的应用 总被引:2,自引:3,他引:2
本文介绍了测定实验室养殖的介形虫Candonarawsoni和水的氧同位素分馏系数,结果表明,这个种属的介形虫壳的氧同位素组成是它所生成环境水的氧同位素组成和水温的函数。因此,介形虫壳的氧同位素组成是一个很好的水化学环境指示计。本文研究了Candonarawsoni的脱壳温度范围,发现它可以在很宽温度范围内脱壳及生长新壳。由于季节温度变化很大,所以用介形虫壳的地球化学指标研究古环境的变化时,每个样品都要采集较多的个体介形虫壳,以使其分析结果能代表年平均温度。 相似文献
97.
Katrina Allen Kennedy 《Journal of Paleolimnology》1994,10(2):69-84
Medicine Lake is a highly saline, meromictic, magnesium sulfate, closed-basin lake in northeastern South Dakota. The geochemical, mineralogical, and magnetic stratigraphies of sediments deposited from about 10.8 to 4.5 ka B.P. document the evolution of the saline brine in response to climatic change in the early to mid-Holocene. During the spruce occupation of the Medicine Lake catchment (10.8–10.0 ka B.P.), dark-grey massive basal sediments with low total-sulfur and carbonate content, upwardly increasing organic-carbon content, and high magnetic susceptibility were deposited in a deep freshwater lake. As the vegetation in the area changed from spruce to birch to oak and elm and finally to prairie between 10.0 and 9.2 ka B.P., and as the lake became shallow and salinity increased from <2 to >10%, light-and dark-grey calcareous and organic-carbon-rich banded sediments with low total-sulfur content and low magnetic susceptibility were deposited. Previous studies have shown that during the forest/prairie transition the lake then changed abruptly from fresh to saline as it lost a substantial portion of its volume. During the early prairie period (9.2–5.5 ka B.P.), alternating sections of aragonite-rich laminae and grey massive sediments with high total-sulfur content and multiple gypsum layers were deposited in a meromictic environment under conditions of fluctuating lake levels and salinity. Continued aridity during the mid-Holocene (5.5–4.5 ka B.P.) probably maintained the lake at relatively low levels and high salinity as dark-grey generally massive sediments with moderate total-sulfur, carbonate, and organic-carbon content and no measurable magnetic susceptibility were deposited. 相似文献
98.
许家窑泥河湾河-湖相沉积物磁化率(k)、天然剩磁(NRM)、饱和等温剩磁(SIRM4T)、非磁滞剩磁(ARM)及S比率(IRM-0.3T/IRM4T)等磁学参数与深海氧同位素的对比分析结果显示:1)许家窑泥河湾层从布容/松山界线到氧同位素阶段5(0.13MaB.P.)基本上是连续沉积,沉积速率保持在约2.45cm/103a左右;2)与同期形成的黄土高原黄土-古土壤序列类似,许家窑河-湖相层也很好地记录了当时中国北方的第四纪气候和环境特征,其典型特征为冰期时高矫顽力赤铁矿含量的显著增加,而间冰期则以低矫顽力的磁铁矿及磁赤铁矿为主要载磁矿物;3)由尝试建立的S比率时间标尺所确定的许家窑古人类遗址处的地层年代约0.5MaB.P.,与先前报道的化石的UTh绝对年龄(0.1MaB.P.)不一致;4)与k相比,S比率与SIRM更适合作为河-湖相沉积物的古气候替代性指标;5)以2.45cm/103a的沉积速率来推算,沉积物的主要物质来源为正常的河-湖相沉积,而直接接受的类似于黄土状的粉尘并不占主导地位 相似文献
99.
Quantitative reconstruction of the lake water paleotemperature of Daihai Lake, Inner Mongolia, China and its significance in paleoclimate 总被引:5,自引:2,他引:5
By measuring Sr/Ca ratios of the ostracod shells (Limnocthere cf. inopinata) in sediments of the Daihai Lake, and combined with Sr2+/Ca2+ ratios of the lake water, this paper obtained paleosalinity of the lake water. Vaporizing experiment of the lake water in
laboratory showed that there was a quantitative relationship between salinity and oxygen isotope. Using this relationship,
oxygen isotope values of the paleo-lake water were calculated. By measuring the oxygen isotope of the authigenic carbonate
in the lake’s sediments, and in combination with the oxygen isotope values of the paleo-lake water, the paleotemperature of
the lake water was calculated. Finally, based on these proxies, the paleoclimate in the lake basin was explored. 相似文献
100.