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581.
本文报道了南海北部深海沉积物中花粉的研究结果。所研究的17940孔长13.30m,包括最近4万年的沉积物。共鉴定统计103个样品,样品间距10cm,分辨率约为360a,自下而上分为3个花粉带和8个亚带。P1带(13.06~8.70m,约37000~15000aB.P.)以山地针叶树(Picea,Abies,Tsuga)花粉高含量组合与蒿属花粉占优势组合交替出现为特征,指示冷湿及温干频繁交替的气候。根据氧同位素资料该带相当于3期及本次盛冰期。P2带前期(P2-a亚带,8.70~7.23m,约15000~11300aB.P.)热带-亚热带常绿阔叶乔木花粉增加指示气候变暖,其中14000aB.P.前后红树林的高峰可能是海平面一度上升的结果;P2带后期P2-b亚带(7.23~660m,约11300~10000aB.p.)高山雨林及山地针叶树花粉增加指示气候变冷。根据氧同位素资料P2-a亚带与Bφlling-Allerφd升温期相当,而P2-b亚带属新仙女木期。P3带(660~0m,10000aB.P.至现在)为全新世,花粉组合以松属花粉占绝对优势,与现代南海北部表层沉积物中花粉组合相似,说明近万年以来南海北部气候与现代气候相近。近1400年来芒其孢子突然增加说明人类活动加剧。 相似文献
582.
南海深海沉积物花粉记录的快速气候波动事件 总被引:10,自引:2,他引:8
本文根据17940柱状样花粉研究结果,分析了南海末次冰期以来千年尺度气候波动事件,并利用频谱分析方法得到南海深海沉积物花粉记录的气候变化的周期。本文研究认为,这种千年级准周期的气候波动可能与高纬度地区的亚米兰科维奇准周期性事件进行对比;它也可能反映了E1Nino-SouthernOscillation(ENSO)系统较长周期的变化,其形成和演化机制仍待进一步探讨。 相似文献
583.
Margarita Caballero Socorro Lozano Beatriz Ortega Jaime Urrutia Jose Luis Macias 《Journal of Paleolimnology》1999,22(4):399-411
Paleoenvironmental studies have documented the late Pleistocene to Holocene evolution of the lakes in the central and southern parts of the basin of Mexico (Texcoco and Chalco). No information was available, however, for the lakes in the north-eastern part of this basin. The north-eastern and the central and southern areas represent, at present, different environmental conditions: an important gradient exists between the dry north and the moister south. To investigate the late Pleistocene to Holocene characteristics of the north-eastern lakes in the basin of Mexico two parallel cores (TA and TB) were drilled at the SE shore of Lake Tecocomulco. Stratigraphy, magnetic properties, granulometry, diatom and pollen analyses performed on these sediments indicate that the lake experienced a series of changes between ca. > 42,000 yr BP and present. Chronological control is given by five radiocarbon determinations. The base of the record is represented by a thick, rhyolitic air-fall tephra that could be older than ca. 50,000 yr BP. After this Plininan event, and until ca. 42,000 yr BP, Lake Tecocomulco was a moderately deep, freshwater lake surrounded by extended pine forests that suggest the presence of cooler and moister conditions than present. Between ca. 42,000 and 37,000 yr BP, the lake became shallower but with important fluctuations and pollen suggests slightly warmer conditions. Between ca. 37,000 and 30,000 yr BP the lake experienced two relatively deep phases separated by a dry interval. A second Plinian eruption, represented in the sequence by a dacitic an air-fall tephra layer dated at 31,000 yr BP, occurred in the area by the end of this dry episode. Between ca. 30,000 and 25,7000 yr BP Tecocomulco was a fresh to slightly alkaline lake with a trend towards lower level. After ca. 25,700 yr BP very low lake levels are inferred, and after ca. 16,000 yr BP the data indicate the presence of a very dry environment that was persistent until the middle Holocene. After 3,500 yr BP lacustrine conditions were re-established and the vegetation cover shows a change towards higher percentages of herbaceous taxa. 相似文献
584.
Mats G. Eriksson Raymonde Bonnefille Forename Surname Séverine Lafon 《Journal of Paleolimnology》1999,22(4):457-473
Variations in pollen assemblages and in physical and chemical composition of a dated sediment record from the small Lake Haubi in north central Tanzania, reveal lake level fluctuations since the late 19th century. Lake Haubi changed from a seasonally inundated swamp to a lake in the beginning of the 20th century. With the exception of 1942-44, when it dried out completely, it remained water filled until 1994 when it again turned into a swamp. The lake level fluctuations in Lake Haubi are largely in phase with fluctuations of the larger East African lakes levels during the 20th century, and are therefore interpreted as being mainly controlled by regional climatic fluctuations. However, the initial formation of Lake Haubi at the turn of the century was likely due to local catchment specific causes, e.g. changes in land use, as the rapid increase in the water level at this time does not correspond to other lake level records from the region. 相似文献
585.
Two varve counts made nearly 20 yrs apart and by different authors in the small and well sheltered meromictic lake of Valkiajärvi were compared with a view to establishing how similar, or otherwise, these two independent varve chronologies might be. The results were significant, the difference between the two varve counts being less than 2% for most of the sediment length, even though the average varve thickness was only 0.3 mm. The continuous and essentially uniform varve record - so far the longest in Finland - covers 8400 yrs and could be applied for accurate dating of palaeoenvironmental indicators in the sediment. As an example, we present a varve-dated pollen diagram for Lake Valkiajärvi.In addition, some magnetic parameters (susceptibility, ARM, SIRM) were measured on the sediment sequence to support the stratigraphic division and correlation of the cores, and to outline the development of the basin since the last deglaciation. Magnetic variables reflected mainly the variation in minerogenic material in the sediment, and were therefore related to changes in the catchment. The magnetic parameters also showed a drastic change some 6000 yrs ago, the reason for which, unfortunately, is still not fully understood. 相似文献
586.
IntroductionInPAGESofIGBPcoreprojectstudy',pollenanalysisinsbeenoneoftheimportantmethodstoreco~ctQuaternarypaleoclilnate.Recently,tviththedeepeningofglobalchangeresearches,manyresearchersactounderstandindetaildiechangeofclimatebystUdyingpollenrecordsoflandsoilsandlakesandswamps.Foralongbine,theChinesescienhstshavepaidgreatattenhontotheStUdyofthehistoricalclinistcandenvironmentchangesinNorthChina.particularlyinBedingarea.Daingthepastthreedecades,thescienhstShavemadesurveysandstUdiesonth… 相似文献
587.
孢粉-气候对应分析重建上海西部地区8.5 ka B.P.以来的气候 总被引:11,自引:0,他引:11
利用现代和化石孢粉资料,借助于对应分析方法,进行了古气候定量重建尝试,取自中国东部区域的表土层孢粉数据被用来建立孢粉-气候转换函数,对取自上清青浦县赵巷有^14C测年的钻孔孢粉数据进行转换,重建了上海地区8.5kaB.P.以来年年温度和降雨量系列,结果表明:约8.5kaB.P.以来,本区温度和降雨量持续升高,约8.2-6.0kaB.P.期间为全新世气候适宜期,年均温和降水量值平均高于现今值0.9℃和160mm,约8.0kaB.P.达到最高值(湿度和降雨量为18.5℃和1575mm);但气候波动剧烈;约6.0-4.0kaB.P.期间为温凉干燥期,气候波动平缓,年均温度和降雨量平衡低于现今值,最低值为13.5℃和827mm(4.1kaB.P.);约4.0-2.0kaB.P.,期间温度和降水回升,但暖湿程度远不及全新世大暖期。2.0kaB.P.以来温度和降雨又呈下降趋势。8.0kaB.P.、7.6kaB.P.和27kaB.P.前后的出现高温高湿峰值,7.5kaB.P.、7.3kaB.P.和4.0kaB.P.前后出现低温低湿谷值。气候变化对本区古文化的发展可能有重要影响。 相似文献
588.
589.
590.
云南拱王山冰蚀湖相沉积剖面全新世孢粉记录与环境 总被引:5,自引:0,他引:5
对云南小江流域拱王山老碳房冰蚀湖相沉积剖面进行孢粉分析,结果显示,研究区自全新世以来经历了5次较明显的气候波动,即9 455~8 635 a(cal.)B.P.气候凉湿;8 635~7 095 a(cal.)B.P.气候冷湿;7 095~5 041a(cal.)B.P.气候寒冷而干燥;5 041~2 529 a(cal.)B.P.气候以凉湿为主;2 529 a(cal.)B.P.以来气候温暖湿润。分析结果与目前中国全新世新冰期与高温期交替及其气温变化规律有一定的差异。 相似文献