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1.
通过对花海古湖泊沉积剖面8.42~0.405 m沉积物样品的矿物和化学元素测定,分析了沉积物中盐类矿物含量及化学元素K/Na比值的变化情况,结合已有的年代地层结果,重建了花海古湖泊10.47~5.5 cal ka BP湖水盐度变化. 结果表明：花海湖泊全新世湖相沉积阶段中,除个别层位以硫酸盐类矿物沉积为主外,早全新世(10.47~8.87 cal ka BP)和中全新世(8.87~5.5 cal ka BP)均以碳酸盐盐类矿物沉积为主,并且早全新世时期K/Na高于中全新世时期,揭示了早全新世时期湖水盐度高于中全新世时期. 这一结果与该湖泊沉积过程所揭示的湖泊水位变化、粒度等揭示的有效湿度变化具有一致性,表明花海湖泊早、中全新世湖水盐度的高低可以指示其湖泊水位的变化,并间接反映了有效湿度的变化. 结合花海湖泊晚全新世湖泊萎缩、气候干旱的特点,该区域早、中、晚全新世气候干湿变化变化模式可以概况为早全新世降水增强、气候呈现由干向湿的转变,中全新世有效湿度最大,晚全新世气候干旱. 这种全新世气候干湿变化模式有别于西风区,亦与季风区不完全相同,呈现出了一种季风-西风过渡带全新世气候干湿变化的模式. 相似文献
2.
干旱区湖泊沉积物粒度组分记录的区域沙尘活动历史: 以新疆巴里坤湖为例 总被引：9，自引：2，他引：7
根据中国西北干旱区巴里坤湖BLK 1剖面沉积物的粒度分析,采用粒级—标准偏差法提取了对沉积环境变化敏感的粒度组分。结果表明,巴里坤湖沉积物中45～170 μm粒级组分含量和平均粒径对研究区区域性风沙活动较为敏感,据此结合14C测年数据重建了研究区9400 cal aBP以来的风沙活动历史。在过去的2 000年内,巴里坤湖地区尘暴事件多发或强风沙活动时段主要出现在240～440 cal aBP、600～1 280 cal aBP和1 400～1 800 cal aBP期间,这些时段同历史时期的雨土频率高值期、古里雅冰芯阴阳离子高含量期较为一致。从更长地质时期来看,8 000～8 300 cal aBP、7 400～7 700 cal aBP、6 500～7 000 cal aBP时段,特别是在中全新世(3 900～6 100 cal aBP)期间,区域性的尘暴事件或强风沙活动尤其频繁,这些时段同古里雅冰芯中微粒浓度、敦德冰芯中的微粒含量记录均可以进行良好的对比。干旱区封闭湖泊沉积是记录地质历史时期风沙活动的良好载体,但由于气候环境变化往往具有较强的区域性特征,因此,对某一剖面沉积物环境敏感粒度组分的提取及应用不具有普适性。 相似文献
3.
对位于新疆北部阿勒泰地区福海县的乌伦古湖WLG10C孔岩芯进行了环境磁学分析,以平行孔(WLG10B) AMS14C测年为年代框架,重建了该地区全新世以来气候环境变化.结果显示:1)乌伦古湖磁性矿物以细颗粒亚铁磁性矿物为主,并含有少量不完整反铁磁性矿物和富铁绿泥石类粘土顺磁性矿物,磁学参数xARM和xARM/x可用作气候变化代用指标,记录了研究区气候环境变化;2)研究区在全新世早期(7300cal.aB.P.以前)为冷干气候,中、晚全新世(7300cal.aB.P.以来)为暖湿气候.在4600cal.aB.P.左右为该湖高湖面时期,在3500 ～2500cal.aB.P.之间存在与全球范围一致的突发冷事件.乌伦古湖全新世气候变化与周边环境记录较一致,气候变化模式符合中亚干旱区全新世气候变化西风模式. 相似文献
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5.
内蒙古达里湖全新世有机碳氮同位素记录与环境演变 总被引：1，自引：0，他引：1
内蒙古中东部的达里湖为一水文封闭型湖泊,位于现今东亚夏季风的北部边缘区,对区域环境变化十分敏感.本文对达里湖沉积中心提取的岩芯(DL04沉积岩芯)顶部8.5m沉积物进行了有机地球化学分析.15个全岩样品有机质的放射性碳测年结果表明:岩芯顶部8.5m涵盖了过去大约11500年.按约50年分辨率分析的225个总有机碳(TOC)、总氮(TN)含量、总有机碳/总氮(C/N)原子比值数据以及221个有机碳和有机氮稳定同位素(δ13C和δ13C)数据,详细揭示了全新世东亚夏季风边缘区的水文和生态变化历史.在距今11500 ～ 9800日历年(ca1.aB.P.)期间,所有地球化学指标均呈逐渐增大趋势,指示入湖河流逐渐增强,达里湖开始扩张,水生植物生产率逐渐升高;在9800 ～ 7700cal.aB.P.期间,TOC和TN含量以及C/N比值维持稳定高值,δ13C和δ15N值较小,指示湖泊维持高湖面状态,陆源输入和浮游植物生产率较高;在7700～ 5900cal.aB.P.期间,C/N比值和δ15N维持低值,TOC和TN含量呈现更高值,并且波动变化,δ13C值逐渐增大,表明湖面维持高水平,湖水显著变暖,浮游植物生产率显著升高,流域植被大幅度扩张;在5900 ～ 4850cal.aB.P.期间,TOC和TN含量,C/N比值以及δ13C值显著减小,δ15N值显著增大,暗示地表径流显著减弱,达里湖湖面显著下降,湖泊生产率快速下降;从4850cal.a B.P.开始,TOC和TN含量以及C/N比值呈逐渐减小趋势,δ13C和δ15N值呈逐渐增大趋势,表明湖面逐渐下降,湖水盐度、碱度升高,湖水可能变冷,湖泊生产率逐渐下降,流域植被收缩.全新世东亚夏季风边缘区水文和生态环境的变化可能直接或间接受北半球夏季太阳辐射量和区域季风降水强度的共同控制. 相似文献
6.
猪野泽记录的季风边缘区全新世中期 气候环境演化历史* 总被引：4，自引：16，他引：4
通过季风边缘区石羊河古终端湖猪野泽QTL剖面年代学及沉积物粒度、碳酸盐、有机碳、碳氮比和有机质稳定同位素等多项气候代用指标的综合分析,建立了季风边缘区9~3cal.kaB.P. 的古气候演化序列。结果表明,9cal.kaB.P. 到7.8cal.kaB.P. 期间,流域的水分条件和温度逐渐上升,植被状况好转,此时气候逐渐转暖湿;而在7.8~7.5cal.kaB.P. 出现了显著的百年尺度的干旱事件,沉积物主要以砂质沉积为主,此时湖泊生产力显著下降;全新世期间最为暖湿的气候适宜期出现在7.5~5.0cal.kaB.P.;约5.0cal.kaB.P. 以来,该区域出现了较为明显的干旱化趋势。另外,对猪野泽地区的白碱湖的湖泊地貌学和年代学研究表明该区域在7.5~5.0cal.kaB.P. 出现了3次高湖面,并且湖岸堤时序变化指示了全新世后半期湖泊逐渐退缩的过程进而指示该区域出现了显著的干旱化趋势。 相似文献
7.
本文通过对在新疆南部塔里木盆地北缘博斯腾湖采集的一根953cm的岩心进行了早全新世以来的古气候重建。对BSTC2000岩心进行了碳酸盐矿物组成、Ca/1000Sr,有机质TOC,C/N和C/S分析,并结合BSTC2000岩心附近的一个沉积物剖面的孢粉资料,利用多指标重建了8500aBP以来的古气候变化特征。在2个平行岩心中对保存的植物叶片、草籽,以及全有机质进行了9个AMS14C年代测定。8500～8100aBP气候冷湿,钻孔位置为河流-滨湖相环境,沉积物中有3层泥炭层。从8100～6400aBP,气温升高,湖泊扩张,气候暖湿,湖泊可能为最高湖面时期。而从6400～5100aBP湖泊稍微下降,气候变冷。在中全新世晚期从5100～3100aBP气候变得高温干旱,但其间的4400～3800aBP有短暂的气候变冷,早期大量的冰雪融水补给博斯腾湖,使得湖泊水位上升。湖泊的第二个高湖面期是5200～3800aBP。在3100～2200aBP气候冷湿,由于蒸发减弱而湖泊有所扩张,湖泊在3100至2800aBP期间是最后一次短暂的高湖面期。这次短期高湖面后,湖泊由于较长时期的低温而引起的供水减少,湖泊收缩。从2200～1200aBP,气候变得干热,湖泊收缩。尽管从1200aBP以来,温度有所下降,气候变得暖干,湖泊又开始有所上升,但是没有达到博斯腾湖出水口孔雀河的海拔高度。 相似文献
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通过对新疆博斯腾湖湖芯沉积物中有机质饱和烃、有机质碳同位素组成(δ~(13)C_(crg))以及与前人得到的环境代用指标结果综合分析,重建了博斯腾湖从早全新世晚期以来古生态环境和湖泊水文的变化历史。结果表明,博斯腾湖大约在8130cal.a B.P.之前气候冷湿,湖泊不发育;约在8130~6400cal.a B.P.为暖湿的全新世适宜期,博斯腾湖流域降水和开都河径流量增加,湖泊水位上升外溢,水生植物及陆生植物发育;6400~5500cal.a B.P.左右冷湿,有效湿度较高,湖泊仍处于较高水位;5500~3000cal.a B.P.左右气候波动明显,为温干时期,而大约在4500—3900cal.a B.P.期间降温,为冷干环境;3000cal.a B.P.以来气温降低,2300~1250cal.a B.P.左右气温有所回升,大约自1250cal.a B.P.以来博斯腾湖地区自然环境逐渐干旱恶化,陆生植物发育较差,而湖泊中沉水植物发育较好。 相似文献
9.
《地层学杂志》2015,(1)
通过对安徽巢湖西岸杭埠河入口三角洲地区CH孔岩芯湖泊相沉积物的色度、磁化率及地球化学等古环境代用指标的分析与研究,揭示了巢湖地区早全新世时期(11.7~7.5cal.kaBP)的极端气候事件。研究表明:研究区11.7~7.5cal.kaBP期间沉积环境极不稳定,气候波动明显,并分别约在7.8cal.kaBP,8.6cal.kaBP,9.4cal.kaBP,10.5cal.kaBP,11.4cal.kaBP出现5次显著的冷干气候事件,且以8.6cal.kaBP与11.4cal.kaBP表现最为强烈,与我国冰芯、石笋及湖泊沉积物所记录的早全新世冷事件具有可比性,反映了巢湖湖泊沉积物对我国早全新世北半球中纬度地区的季风气候有明显的响应,这将为我国北半球早全新世气候波动的机理研究提供佐证。 相似文献
10.
兴凯湖沉积物有机碳和氮及其稳定同位素反映的28kaBP以来区域古气候环境变化 总被引：2，自引：0，他引：2
兴凯湖是东北亚最大的淡水湖,也是中俄界湖。我们是国内首次对兴凯湖一根长269 cm的沉积岩心进行了研究,结果显示:δ13Corg和TOC之间显示较好的负相关性,说明δ13Corg低值时期,气候温暖或湿润,δ13Corg值处于高值时期,气候冷干;C/N比值和TOC之间显示较好的正相关性,C/N比值平均值为11.4,显示兴凯湖沉积物有机质以内源浮游植物生产为主;δ15Norg高值对应于气候冷干期,此时沉积物有机质更多的来源于浮游植物,δ15Norg低值对应于暖湿期,但营养盐输入的减少也会造成δ15Norg值降低。兴凯湖沉积物有机碳和氮及其稳定同位素数据综合分析结果表明:28 480～26 160 cal.aBP,湖区气候冷干;26 160～22 880 cal.aBP,湖区气候温暖湿润;22 880～18 180 cal.aBP,流域处于末次盛冰期多年冻土环境;18 185～12 650 cal.aBP,对应于Blling/Older Dryas/Allerd气候波动暖期;90～78 cm段,对应于Younger Dryas事件;11 500～4 570 cal.aBP,进入全新世暖湿期,早期气候温干,晚期气候温湿;4 570～1 470 cal.aBP,气候冷干;1470 cal.aBP以来,又转为暖湿气候。 相似文献
11.
Damien Rius Boris Vannière Didier Galop Hervé Richard 《Quaternary Science Reviews》2011,30(13-14):1696-1709
One lake and three peat bogs from the Lourdes glacial basin (France) were used for macrocharcoal analyses and fire frequency reconstruction over the entire Holocene (11700 years). The chronology was based upon thirty-three 14C AMS dates. Comparison of the distribution of both CHarcoal Accumulation Rate (CHAR) and fire return intervals showed that charcoal accumulation significantly differs between the lake and the peat bogs, but that frequency calculation overcomes the disparity between these site types. A composite frequency was built from the four individual records to assess regional versus local variability and fire regime controls by comparisons with regional fire activity, Holocene climatic oscillations and vegetation history. The millennial variability can be depicted as follows: relatively high frequency between 8000 and 5000 cal a BP (up to 5 fires/500 yrs), relatively low frequency between 5000 and 3000 cal a BP (down to 0 fires/500 yrs), and an increase between 3000 and 500 cal a BP (up to 4 fires/500 yrs). From 8000 to 5000 cal a BP, fire frequency displays strong synchrony between sites and appears to be mostly driven by increased summer temperature characterizing the Holocene Thermal Maximum (HTM). On the contrary, during the last 3000 years fire frequency was heterogeneous between sites and most probably human-driven. However, higher frequency at the millennial scale during the mid-Holocene strongly suggests that the perception of human-driven fire regime depends on the strength of natural controls. 相似文献
12.
A continuous record of insect (Chironomidae) remains preserved in lake sediments is used to infer temperature changes at a small lake in Arctic Canada through the Holocene. Early Holocene summers at the study site were characterized by more thermophilous assemblages and warmer inferred temperatures than today, presumably in response to the positive anomaly in Northern Hemisphere summer insolation. Peak early Holocene warmth was interrupted by two cold reversals between 9.5 and 8 cal ka BP, during which multiple cold-stenothermous chironomid taxa appeared in the lake. The earlier reversal appears to correlate with widespread climate anomalies around 9.2 cal ka BP; the age of the younger reversal is equivocal but it may correlate with the 8.2 cal ka BP cold event documented elsewhere. Widespread, abrupt climate shifts in the early Holocene illustrate the susceptibility of the climate system to perturbations, even during periods of enhanced warmth in the Northern Hemisphere. 相似文献
13.
Ulrike Hoff Oleg Dirksen Veronika Dirksen Gerhard Kuhn Hanno Meyer Bernhard Diekmann 《Boreas: An International Journal of Quaternary Research》2014,43(1):22-41
Holocene palaeolimnological conditions were reconstructed by analysing fossil diatom assemblages within a lacustrine sediment core from Lake Sokoch, southern Kamchatka (Russia). Sediments of this proglacial lake cover the past 9400 years and hence represent almost the whole Holocene history. The biosiliceous muddy sample material was analysed for several geochemical and biological parameters, such as the total organic carbon and biogenic silica content, and the diatom community (quantitative and qualitative changes). Based on changes in the relative abundances of the most frequent species Aulacoseira subarctica, Staurosira martyi and Stephanodiscus alpinus and a depth‐constrained cluster analyses (CONISS), five diatom assemblage zones could be identified. The oldest stage recovered lies between 9400 and 9000 cal. a BP and reflects the initial lake stage after the retreat of local glaciers, with a high detrital sediment supply, shallow‐water conditions and a high diatom diversity. The next zone (9000–6200 cal. a BP) shows a more mature lake system with accumulating biogenic remains and higher water levels during climate amelioration. This is followed by the most obvious change in the diatom assemblage, delineated by an occurrence of S. alpinus, between 6200 and 2700 cal. a BP. Wet conditions in spring probably led to an enhanced fluvial runoff and eutrophic to hypertrophic conditions. The end of this period might reflect climate deterioration related to the Neoglacial epoch of the Holocene. Between 2700 and 1600 cal. a BP the sediments of Lake Sokoch reveal oligotrophic water conditions in a windy high‐energy environment. The youngest interval, between 1600 cal. a BP and the Present, indicates shallow‐water conditions and a very short growing season, which might reflect the Little Ice Age. The results may offer a baseline for the interpretation of Holocene palaeoenvironmental changes in Kamchatka and their relation to regional climate change from a palaeoecological perspective. 相似文献
14.
Sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high‐resolution millennial to centennial‐scale record of changing climate and catchment hydrology spanning the past ca. 10 000 years. Here, we focus on the period between 9500 ± 25 and 7000 ± 155 cal. yr BP during which grain size, diatom palaeoecology, biogenic silica concentrations, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions, with a significant event commencing at ca. 8240 cal. yr BP, commensurate with a lowering of lake level, faster erosion rates and increased sediment influx with a duration of ca. 360 yrs. However, the changes in the lake are not reflected in the terrestrial vegetation, where the pollen record indicates that podocarp forest dominated the Auckland region, with apparent environmental stability during this part of the early Holocene. The synchronous change in most of the proxies between ca. 8240 and 7880 cal. yr BP at Lake Pupuke indicates the presence of a sustained episode of relatively low lake level and concomitant increased rate of erosion in the early Holocene that appears to be at least partly coeval with the 8200 cal. yr BP meltwater event proposed for the North Atlantic region. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
15.
Rapid Holocene climate changes in the North Atlantic: evidence from lake sediments from the Faroe Islands 总被引：1，自引：1，他引：1
CAMILLA S. ANDRESEN SVANTE BJÖRCK MATS RUNDGREN DANIEL J. CONLEY CATHERINE JESSEN 《Boreas: An International Journal of Quaternary Research》2006,35(1):23-34
Holocene records from two lakes on the Faroe Islands were investigated to determine regional climatic variability: the fairly wind-exposed Lake Starvatn on Streymoy and the more sheltered Lake Lykkjuvötn on Sandoy. Sediment cores were analysed for content of biogenic silica, organic carbon and clastic material, and magnetic susceptibility. In addition, a new qualitative proxy for past lake ice cover and wind activity was developed using the flux of clastic grains that are larger than 255 μm. Both long-term and short-term climatic developments were similar between the two lakes, suggesting a response to a regional climate signal. The long-term climate development is characterized by early Holocene rapid warming followed by Holocene climatic optimum conditions ending around 8300 cal. yr BP. A more open landscape as evidenced from increased sand grain influx in the period 8300–7200 cal. yr BP could reflect the aftermath of the 8200 cal. yr BP event, although the event itself is not recognized in either of the two lake records. From around 7200 cal. yr BP the mid-Holocene climate deterioration is observed and from 4200 cal. yr BP the climate deteriorated further with increased amplitude of centennial cooling episodes. 相似文献
16.
Predominantly laminated lake sediments from a saline closed‐basin lake on the northeastern Tibetan Plateau were investigated using a multi‐proxy approach (14C‐accelerator mass spectrometry dating, smear‐slide analysis, loss on ignition, grain size, X‐ray diffraction, elemental concentration, ostracod assemblages, stable isotopes of ostracod shells) to trace the regional environmental and climatic history in the Lateglacial and Holocene. Before about 15 cal. ka BP, small saline water bodies probably filled the basin under unstable cold and harsh environmental conditions. Soon after about 14.9 cal. ka BP, a relatively deep saline lake was established, probably as a result of runoff from melting snow, ice and frozen ground in the lake's catchment. Large changes in flux of aeolian material to the lake were recorded during this initial period of formation of Lake Kuhai. Highest lake levels, a low sediment accumulation rate and less saline conditions were maintained between about 12.8 and 7.1 cal. ka BP when the aeolian influx diminished significantly. After about 7.1 cal. ka BP, the aeolian influx remained at a moderate level apart from a strongly increased dust delivery to the lake between about 6.1 and 5.4 cal. ka BP and a minor short‐lived period of slightly enhanced aeolian influx at about 2.7 cal. ka BP. The strongly enhanced dust input to the lake between 6.1 and 5.4 cal. ka BP represented the largest influx of aeolian material to Lake Kuhai during the entire Holocene. However, evidence for climatic deterioration during this period is not seen at most other palaeoclimate sites on the Tibetan Plateau, but instead a significant increase in aridity has been recorded at numerous sites in the northern foreland of the Tibetan Plateau and on the Chinese Loess Plateau. The large dust input to Lake Kuhai between 6.1 and 5.4 cal. ka BP probably did not result from a severe climate deterioration on the Tibetan Plateau itself, but from the pronounced aridity in its northern and eastern foreland. In contrast, the increase in dust influx about 2.7 cal. ka BP seems to correspond to a brief warming spell recorded at other sites on the Tibetan Plateau too. A slight increase in lake level and decrease in salinity after about 0.6 cal. ka BP suggests a slightly higher effective moisture during the final lake stage, accompanied by a somewhat larger dust influx. This apparent contradiction possibly results from enhanced human activities on the northeastern Tibetan Plateau during the last 600 years. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
17.
Previous studies have demonstrated long‐term changes in effective moisture in sub‐Saharan Africa. Here, we reconstruct Holocene environments using a ～7 m lake‐sediment sequence recovered from the northeastern Nigerian Sahel and attempt to distinguish basin‐specific changes from regional climatic variations. The sequence was analysed for sedimentological properties, mineral magnetism and pollen, and dated by 137Cs, 210Pb excess and 14C. Extremely arid conditions of the terminal Pleistocene ended ca. 11 500 cal. BP (calendar years) when climate ameliorated and a lake developed until the occurrence of an arid event leading to lake desiccation at ～11 200 cal. BP. Following this, climate ameliorated and a water body re‐emerged. Very wet conditions predominated 11 200–5600 cal. BP, followed by drought between 5600 and 5500 cal. BP and a return to moderate humidity from 5500 to 4000 cal. BP. After 4000 cal. BP, a marked deterioration occurred, culminating in lake desiccation at ca. 800 cal. BP. After this time the climate remained generally dry and the re‐emerging lake was shallow. Comparison of these results with other well‐dated sequences in the region demonstrates the importance of basin‐specific influences on the palaeolimnological records in addition to regional climatic controls. Disentangling these different controls, as well as the reconstruction of Holocene climate, therefore requires a multiple‐basin approach. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
18.
LOVISA ZILLÉN IAN SNOWBALL 《Boreas: An International Journal of Quaternary Research》2009,38(3):493-503
Mineral magnetic and carbon analyses of a continuous varved lake sediment sequence in west-central Sweden (Lake Mötterudstjärnet) complement similar palaeoclimate proxies obtained from two varved lake sediment sequences in northern Sweden and one in central Finland. The varve chronology is supported by tephrochronology, palaeomagnetic secular variations and 14 C AMS dating of terrestrial macrofossils. We apply a simple model in which the transport and deposition of catchment mineral matter reflect the amount of winter snow accumulation, spring snow-melt and stream discharge. Our data show that winter snow accumulation was generally enhanced in Sweden between 8100 and 7750 cal. yr BP. If dating errors are taken into account, the 350-year period of increased erosion is the geomorphic response to a multi-centennial scale climatic cooling that occurred some time between 8500 and 7500 cal. yr BP. The most significant erosion event in central Sweden was centred at 8050 cal. yr BP. It lasted 150 years (between 8100 and 7950 cal. yr BP) and is equivalent to the most extreme Holocene climate anomaly in the northern hemisphere, known as the 8 ka or 8200 cal. yr BP climate event. Our high-resolution paramagnetic susceptibility and ferrimagnetic grain-size parameters suggest that snowpack accumulation increased most significantly in northern Sweden between 7900 and 7750 cal. yr BP. We suggest that this north–south difference was a response to the re-establishment of moisture-laden westerly air masses, as meridional Atlantic overturning circulation was re-established at the beginning of the Holocene thermal maximum. 相似文献
19.
A Holocene lake sediment record is presented from Lake N14 situated on Angissoq Island 15 km off the main coast of southern Greenland. The palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility. A total of 43 radiocarbon dates has ensured a reliable chronology. It is argued that varying sediment composition mainly reflects changing precipitation. By analogy with the present meteorological conditions in southern Greenland, Holocene climate development is inferred. Between 11 550 and 9300 cal. yr BP temperature and precipitation increase markedly, but this period is climatically unstable. From 9300 yr BP conditions become more stable and a Holocene climatic optimum, characterised by warm and humid conditions, is observed from 8000 to 5000 cal. yr BP. From 4700 cal. yr BP the first signs of a climatic deterioration are observed, and from 3700 cal. yr BP the climate has become more dry and cold. Superimposed on the climatic long‐term trend is climate variability on a centennial time‐scale that increases in amplitude after 3700 cal. yr BP. A climatic scenario related to the strength and position of the Greenland high‐pressure cell and the Iceland low‐pressure cell is proposed to explain the Holocene centennial climate variability. A comparison of the Lake N14 record with a terrestrial as well as a marine record from the eastern North Atlantic Ocean suggests that the centennial climate variability was uniform over large areas at certain times. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
20.
Chironomid remains from a mid-elevation lake in the Sierra Nevada, California, were used to estimate quantitative summer surface water temperatures during the past ∼15,000 yr. Reconstructed temperatures increased by ∼3°C between lake initiation and the onset of the Holocene at ∼10,600 cal yr BP (calibrated years before present). Temperatures peaked at 6500 cal yr BP, displayed high variability from 6500 to 3500 cal yr BP, and stabilized after 3500 cal yr BP. This record generally tracks reconstructed Santa Barbara Basin sea surface temperatures (SSTs) through much of the Holocene, highlighting the correspondence between SST variability and California land temperatures during this interval. 相似文献