青藏高原中部错鄂湖晚新生代以来的沉积环境演变及其构造隆升意义

错鄂湖200m深井岩芯古地磁测年表明,错鄂湖形成于约2．8Ma年前．沉积岩性组合、粒度特征和磁化率变化揭示了约3次大的沉积环境变化过程,反映了至少2次剧烈的青藏高原隆升过程;同时,孢粉组合也揭示了构造隆升导致的植被组合的变化．初步研究认为,大的湖泊沉积环境变化主要是在青藏高原不断隆升的背景上进行的．2．8-2．5Ma和0．8Ma以来的沉积环境演化主要受构造运动的控制,而2．5-0．8Ma环境演化过程更多的受到冰期-间冰期旋回气候变化的影响．     

Establishing a chronology for lacustrine sediments using a multiple dating approach—A case study from the Frickenhauser See, central Germany

In order to establish a reliable chronology for lacustrine sediments of the Frickenhauser See (central Germany) different dating methods have been applied. A total of 17 AMS ¹⁴C dates, all within the last 2000 years, were supplemented with ¹³⁷Cs/²¹⁰Pb dating and varve counting of the uppermost sediments (131 years). The age–depth model for the Frickenhauser See has to cope with highly variable sedimentation rates and overlapping probability distributions of calibrated ¹⁴C dates. The uncertainty of calibrated ¹⁴C dates could be considerably reduced by including the stratigraphic relationship of the dated samples, the age information derived from short-lived isotopes and varve counting as well as an upper and lower limit of realistic sedimentation rates as ‘a priori’ information in the calibration procedure. Sets of possible age combinations obtained by repeated sampling from the modified probability distributions were used to calculate continuous age–depth relationships based on monotonic smoothing splines. The obtained age–depth model for the sediment record of the Frickenhauser See represents the average of over 16,000 such model runs and suggests a drastic increase in sedimentation rates from around 1–2 mm a⁻¹ (200–1000 AD) to over 25 mm a⁻¹ for the period between 1100 and 1300 AD. From then on, sedimentation rates exhibit relatively stable values around 3–9 mm a⁻¹. ‘Conventional’ age–depth models such as general polynomial regression or cubic splines either do not include the obtained age-information in a satisfying manner (the model being too “stiff”) or exhibit “swings” causing age-reversals in the model. Although the age–depth relationships obtained for monotonic smoothing splines and mixed-effect regression are generally very similar, they differ in their respective sedimentation rates as well as in their uncertainties. Mixed-effect regression resulted in much higher sedimentation rates of more than 37 mm a⁻¹. These results suggest that monotonic smoothing splines give better control of the age–depth model characteristics and are well suited in situations, where the integrity of ¹⁴C dates is high, i.e. the dated material represents the age of the respective layer.     

Holocene climate change in the Central Tibetan Plateau inferred by lacustrine sediment geochemical records

Multi-proxies of lacustrine sediments, such as total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), total sulfur (TS), hydrogen index (HI), oxygen index (OI) and stable carbon isotopic composition of organic matter (δ 13Corg), were analyzed using a 7.3 m core from Zigê Tangco. The source of the organic matter in the sediment was mainly from autochthonous phytoplankton, therefore the significances of proxies can be interpreted as that high TOC, TOC/TS, HI and δ13Corg values, low TC, TIC values corresponded to warm and wet climatic condition, and vice versa. The process of climatic development in the Zigê Tangco region was hence recovered. During the early and Mid-Holocene, the climate was warm and wet and intensive cold events occurred during the periods of 8600 to 8400 cal a BP and 7400 to 7000 cal a BP. In the second half of Holocene, the climate became cold and dry gradually. The palaeoclimatic process during Holocene in Zigê Tangco region matched well with that in Co Ngoin region which is ca 40 km to the south-east. Therefore this palaeoclimatic process represents the Holocene climatic feature in the Central Tibetan Plateau which has the same pattern in the Northern Tibetan Plateau, but the time and duration of some climatic events might be different. We can conclude that in Holocene solar insolation controlled the climatic pattern on the central Tibetan Plateau.     

西藏纳木错表层沉积物中正构烷烃的来源与空间分布特征

通过测定纳木错现代植物和表层沉积物样品中的正构烷烃,结合主成分分析方法,明确了表层沉积物中烷烃的主要来源,并初步分析了它们在湖泊中的空间分布特征.研究结果显示,沉水植物所含烷烃以n-C21-C25为主,具有n-C23的峰值;陆生植物主要含n-C27-C33烷烃,具有n-C29或n-C31的峰值;但垫状点地梅(Androsace tapete)和香柏(Sabina pingii)的主峰碳却是n-C33烷烃,这在以往研究中鲜有报道.在纳木错表层沉积物中,正构烷烃具有典型的n-C31和n-C23双峰分布形式,来源于低等菌藻类、沉水植物以及陆生植物,其中碳数小于C20的短链烷烃主要来源于低等菌藻类,其空间分布均一,由低等菌藻类的浮游生活型所决定;长链烷烃主要来源于高等植物,含量从滨岸到湖中心逐渐减少,这与其在运移和沉积过程中受微生物的持续降解作用有关,此外,来源于陆生植物的n-C27-C33烷烃因河流汇水面积和流量不同而存在空间差异,这值得重视和进一步研究.     

青藏高原南部空姆错湖芯中陆源正构烷烃氢同位素比值的气候意义

在青藏高原南部空姆错钻取了一根浅湖芯,对其中时间跨度约为50年的剖面按7年间隔对其中陆源正构烷烃(C_(25),C_(27),C_(29),C_(31))进行了提取分析。通过将这些生物标志物的氢同位素比值与附近浪卡子气象站和拉萨气象站的气象参数记录进行比较,发现这些生物标志物的δD值与生长季节时段的平均气温显著相关,而与生长季节时段的降雨量和相对湿度的相关性差,说明陆源沉积正构烷烃的氢同位素比值主要记录了气温信号,可以被用于古温度重建。     

可可西里库赛湖KS-2006孔矿物组成揭示的青藏高原北部晚全新世气候变迁

通过对可可西里库赛湖KS-2006孔矿物组合的分析表明:库赛湖沉积的碳酸盐为以文石为主的自生碳酸盐,其含量的高低能够指示温度的变化;盐类矿物只是在2150 cal aBP以来才出现,表明湖水盐度增高,与此同时,石英含量的持续增高可能同冷干气候条件下该区风成活动的加强有关.青藏高原北部晚全新世的气候环境演化过程为:377...     

High-resolution peat records for Holocene monsoon history in the eastern Tibetan Plateau

Holocene peat sediment has been attached impor-tance to reconstruct the Holocene climatic variations because it can provide much palaeoclimatic informa-tion with high resolution. Analysis on the plant mac-rofossil[1], pollen[2―4], isotope ratio[5―9], element con-tent[10,11], total organic carbon (TOC)[12], humifica-tion[13,14] and grayscale[12] for peat sediment has shown its superiorities as a recorder medium for reconstruct-ing the Holocene climate. Hong et al. have done great fruitful w…     

青藏高原达则错近1000年来生态系统变化及可能机制

在全球变化的背景下,厘清湖泊生态系统对气候环境以及人类活动的响应机制对制定社会的适应政策非常重要.目前的研究手段如现场观测和围隔实验等可以很好地揭示湖泊生态系统在有观测记录以来的演替和变化过程,但是不能提供历史时期湖泊生态系统的变化及其对气候环境变化和人类活动的响应.古湖沼学可以为探讨湖泊生态系统的长期变化及其对气候环...     

青藏高原湖泊古今变化的遥感分析—以达则错为例

青藏高原湖泊受人类活动干扰较少,主要受气候变化导致的冰川融化和蒸发的影响,是气候变化直观敏感的反映区。因此,研究青藏高原湖泊变化对区域以至全球气候、环境变化的研究具有深远意义。本文在遥感影像的基础上发展了综合指数计算与空间分异的现存湖迭代提取方法,对影像数据上的湖泊进行动态监测;并结合DEM数据发展了半自动化的古岸线提取方法,进而分析古湖泊的变化,二者相结合直观全面地反映出了青藏高原湖泊的古今变化情况。并以达则错湖为例进行提取,分析了其近25年以来以及大湖期以来的缩减情况     

1950年以来青藏高原兹格塘错碳酸盐稳定碳同位素变化及其原因

兹格塘错是青藏高原中部一个典型的半混合型咸水湖泊。本文在~(210)Pb和~(137)Cs定年的基础上,研究了兹格塘错重力岩芯(ZGTC A-1)小于38.5μm细颗粒组分碳酸盐稳定碳同位素1950年以来的变化及其影响因素。对冬夏季湖水水化学特征的分析表明,夏季湖水溶解CO_2呈逸出状态,冬季湖水钙离子浓度是夏季湖水的10倍,据此可以得出兹格塘错碳酸盐矿物主要在夏季沉淀。通过与那曲气象站气象记录对比发现,1950年以来A-1岩芯碳酸盐碳同位素变化与年均温度有很好的相关性,表现出年均温度高时碳同位素偏重,而年均温度低时碳同位素偏轻的特征。兹格塘错1950年以来自生碳酸盐碳同位素的变化是由湖区及水体碳循环(如碳酸盐沉淀,有机质的沉淀与分解,有机碳和无机碳的转化等)的变化引起的,但各种因素的相互作用非常复杂。碳酸盐含量也与温度有关,温度越高,碳酸盐含量越高,同时降水量与碳酸盐含量也存在明显的相关关系。1950年以来有机质含量与温度呈反相关,可能与湖泊生产力的下降有关。     

Quantitative recuperation of climatic sequences for the last 200 years in Xingcuo Lake,eastern Tibetan Plateau

The functional relation between theδ18O values in the shell of gastropod Gyraulus sibirica and the air temperature in the warm half-yearly period, and that between Sr/Ca ratio and the precipitation in the warm half-yearly period were established by calibrating the δ18O and δ13C values, Sr/Ca ratio and Mg/Ca ratio in the shell Gyraulus sibirica, as well as the total organic carbon (TOC) and its δ13C values in the Xingcuo Lake sediment in the eastern Tibetan Plateau. The sequences of air temperature and precipitation in the last 200 years in the region were quantitatively recuperated on this basis. The results showed the following: (i) There was a negative correlativity between Sr/Ca ratio and the precipitation in the warm half-yearly period, its correlation coefficient was 0.86. (ii) There was an obviously positive correlativity between indexδ18O and the running average temperature in the warm half-yearly period, its correlation coefficient was 0.89. (iii) Evolution of the air temperature and the precipitation in the last 200 years can be divided into three phases distinctly. The precipitation in the later mid-19th century was 220 mm higher than that today; the air temperature in the warm half-yearly period was 2℃ lower than that of the present. The precipitation in the minimum air temperature period of the early 20th century was below that today by 60 mm, and the air temperature in the warm half-yearly period was 3.4℃ lower than that today. (iv) An evidently warming and drying trend existed in the last five decades.     

青藏高原拉昂错热力分层和混合层深度变化特征观测

湖泊热力结构不仅影响湖泊内部生态环境,而且与区域气象和气候系统相互影响,但目前对湖泊垂直温度的观测研究仍非常匮乏.本研究基于青藏高原拉昂错连续的湖温和气象观测,分析了小时尺度和日尺度热力分层规律和混合层深度的变化特征.结果表明:拉昂错为冷多次完全混合型湖泊;湖表温度8月达到最大值,湖面敞水区和沿岸的湖表温度季节震荡相同...     

Sensitivity of the central Asian climate to uplift of the Tibetan Plateau in the coupled climate model (MRI-CGCM1)

Abstract   The relationship between the altitude of the Tibetan Plateau and climate change in central Asia was investigated through a numeric experiment using the Meteorological Research Institute (MRI) coupled atmosphere–ocean general circulation model I (MRI-CGCM1). The results suggest that summer precipitation in central Asia decreased significantly as the Tibetan Plateau rose in height. Spring precipitation, however, increased during initial growth stages when the plateau height was up to 40% of its present-day height, and then decreased with further plateau growth. During the Tibetan Plateau uplift, the difference between precipitation and evaporation was minimal during spring. When the plateau attained a height exceeding 60% of its present height, relatively low precipitation but high evaporation in spring led to a lower amount of ground moisture. In the case of the high plateau, sensible heat flux during summer and fall largely exceeded latent heat flux. Change was particularly significant for cases when the plateau reached 40–60% of its present-day height. The duration of the predominant sensible heat flux became longer with the uplift of the Tibetan Plateau. The period in which latent heat exceeded sensible heat seems to have been restricted to winter and early spring. The numeric experiments suggest that a significant drying of central Asia corresponded to the period in which the Tibetan Plateau exceeded approximately half its present-day height.     

Timing of Holocene lake highstands around Dawa Co in inner Tibetan Plateau: Comparison of quartz and feldspar luminescence dating with radiocarbon age

Lakes over the inner Tibetan Plateau (TP) are very sensitive to the regional environmental transformations and climate changes. Well-preserved lake sediments around these lakes provide critical geomorphological and sedimentary evidence that can be used to infer the past hydroclimate changes. In this study, a lacustrine section from a sandy shoreline (∼74 m above the modern lake) situated to the northwest of modern Dawa Co in the inner TP was investigated using both luminescence and radiocarbon dating methods. Our results demonstrated: (1) the quartz optically simulated luminescence (OSL) dating yielded much younger ages (∼4 ka) than that of the post-infrared IRSL (pIRIR) dating of the K-feldspar fraction; (2) fading test showed g-values ranging between 1.34 and 4.46%/decade for quartz OSL signals, which is considered to be responsible for the underestimation of the corresponding ages; (3) the AMS ¹⁴C age of the charcoal sample from the section is in line with the K-feldspar pIRIR₂₂₅ ages, confirming the reliability of the pIRIR₂₂₅ dates and the underestimation of the quartz OSL ages. The anomalous fading of quartz OSL signals and the consequent age underestimation have been reported in several other lakes on the TP, we presented here for the first time firm evidence of the phenomenon with the help of a robust independent control of AMS ¹⁴C age of the charcoal. Based on the pIRIR₂₂₅ and AMS ¹⁴C ages, we conclude that Dawa Co underwent a prominent highstand during the early Holocene (∼9–7 ka), which was probably controlled by the large amounts of glacial meltwater input and the increased monsoonal precipitation.     

Rapid decrease of mass balance observed in the Xiao (Lesser) Dongkemadi Glacier,in the central Tibetan Plateau

The mass balance of the Xiao (Lesser) Dongkemadi Glacier located in the Tanggula Mountains, of the central Qinghai‐Tibetan Plateau has been monitored since 1989. The results show that the mass balance of the glacier has recently shown a deficit trend, and that the glacial terminus was also retreating. Positive mass balance of the glacier was dominant during the period 1989–1993, and the accumulated mass balance reached 970 mm. However, negative mass balance of the glacier has occurred since 1994, except for the large positive mass balance year 1997. The mass balance was ? 701 mm in 1998, an extremely negative glacier mass balance year. The equilibrium line altitude showed a significant increasing trend. The mass balance of the glacier has changed from a significantly positive mass balance to a strongly negative mass balance since 1994. Meteorological data suggest that the rapid decrease in the mass balance is related to summer season warming. Copyright © 2007 John Wiley & Sons, Ltd.     

可可西里库赛湖揭示的青藏高原北部近4000年来的干湿变化

通过青藏高原北部可可西里库赛湖KS-2006孔(深637cm)沉积岩芯总有机碳、总氮含量及沉积物粒度变化的研究,恢复了该地区近4000年来的干湿变化历史.结果表明,该地区近4000年来经历了显著的干湿变化,干旱时段出现在3900-3590cal aBP、3320-2630cal aBP、1720-1420cal aBP及1100-840cal aBP期间:湿润时段出现在3590-3320cal aBP、2630-1720cal aBP、1420-1100cal aBP以及840cal aBP之后小冰期有效降水升高的相对湿润时期.区域对比分析表明库赛湖地区近4000年来的干湿变化受亚洲季风影响;同时,该地区存在明显的中世纪暖期及小冰期的三次降温事件记录.     

藏南冰前湖枪勇错近百年沉积速率变化及冰川进退反演

青藏高原上分布着大量的大陆性冰川,其对区域及全球气候变化响应极其敏感.工业革命以来,随着全球升温速率加快(特别是北半球),青藏高原部分地区的冰川在近百年显著退缩.冰前湖沉积物是最直接的冰川变化记录载体之一,但其沉积速率如何响应冰川及气候变化,能否反演冰川进退过程却知之甚少.本文依据210pb和137 Cs限定藏南冰前湖...     

Sedimentation and chronology of heavy metal pollution in Oslo harbor, Norway

Stratigraphic profiles of Cu, Cd and Hg in ten sediment cores from the Oslo harbor, Norway, combined with results of radiometric dating demonstrate that pollution by these metals peaked between 1940 and 1970. Dating results indicate that Hg discharges peaked between 1940 and 1950, Cd reached maximum ca. 1955-1960, and Cu has the highest concentration in sediment interval corresponding to ca. 1970. Geochemical profiles and maxima of Cu, Cd and Hg concentrations can be used as chronostratigraphic markers for sediment cores from the Oslo harbor. Acoustic backscatter and sediment core data indicate that propeller wash affects the seabed in the Oslo harbor. The propeller-induced turbulence causes erosion, and in places exposes and remobilizes contaminated sediments that accumulated in the harbor during previous decades. Such re-exposure of contaminated sediments could be detrimental to local ecosystems and offset remediation efforts, warranting further impact studies and potential mitigation strategies to prevent redistribution.