Late Glacial and Holocene Palaeoenvironmental Changes in the Rostov-Yaroslavl’ Area, West Central Russia     

Barbara Wohlfarth  Pavel Tarasov  Ole Bennike  Terri Lacourse  Dmitry Subetto  Peter Torssander  Fedor Romanenko 《Journal of Paleolimnology》2006,35(3):543-569

Three lake sediment sequences (lakes Nero, Chashnitsy, Zaozer’e) from the Rostov-Jaroslavl’ region north of Moscow were studied to provide information on palaeoclimatic and palaeoenvironmental changes during the past 15,000 cal yr. The multi-proxy study (i.e., pollen, macrofossils, mineral magnetic measurements, total carbon, nitrogen and sulphur) is chronologically constrained by AMS ¹⁴C measurements. Lake Nero provided the longest sedimentary record back to ca. 15,000 cal yr BP, while sediment accumulation began around ca. 11,000 cal yr BP in the two other lakes, possibly due to melting of permafrost. Limnic plant macrofossil remains suggest increased lake productivity and higher mean summer temperatures after 14,500 cal yr BP. While the late glacial vegetation was dominated by Betula and Salix shrubs and various herbs, it appears that Betula sect. Albae became established as early as 14,000 cal yr BP. Major hydrological changes in the region led to distinctly lower lake levels, starting 13,000 cal yr BP in Lake Nero and ca. 9000 cal yr BP in lakes Chashnitsy and Zaozer’e, which are situated at higher elevations. These changes resulted in sedimentary hiatuses in all three lakes that lasted 3500–4500 cal yr. Mixed broad-leaved – coniferous forests were widespread in the area between 8200 and 6100 cal yr BP and developed into dense, species-rich forests between 6100 and 2500 cal yr BP, during what was likely the warmest interval of the studied sequences. Agricultural activity is documented since 500 cal yr BP, but probably began earlier, since Rostov was a major capital by 862 A.D. This apparent gap may be caused by additional sedimentary hiatuses around 2500 and 500 cal yr BP.  相似文献   

Fire and vegetation history during the last 3800 years in northwestern Montana   总被引：1，自引：0，他引：1  

Mitchell J. Power  Cathy Whitlock  Patrick Bartlein  Lora R. Stevens 《Geomorphology》2006,75(3-4):420

Foy Lake in northwestern Montana provides a record of annual-to-decadal-scale landscape change. Sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years, which were then compared to similar records from AD 1880 to 2000. The long-term record at Foy Lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change. Fire activity (inferred from the frequency of charcoal peaks) averaged 18 fire episodes/1000 years from 3800 to 2125 cal year BP, and increased from 16 fire episodes/1000 years at 2125 cal year BP to 22 episodes/1000 years at 750 cal year BP, a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover. Between 2125 and 750 cal year BP, increased forest cover produced more background charcoal than before and after this period, when vegetation was dominated by steppe. Between 750 and 75 cal year BP steppe has expanded and fire episode frequency averaged 33 episodes/1000 years, increasing to a maximum of 40 episodes/1000 years at ca. 300 cal year BP and then decreasing to present levels. Since AD 1880, the pollen record indicates an increase in shrubs and grasses from AD 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing. No fires have been documented in the Foy Lake watershed since AD 1880. Charcoal from the extralocal fires of AD 1910, burning over 4,111,249 ha in Idaho, Montana, and Wyoming, however, is present in Foy Lake. Between AD 1970 and 2000, increased arboreal pollen in the record is consistent with observations that the forest has become more closed. The activities of Euro–Americans have led to a decline in forest cover between AD 1880 and 1970, followed by a recent increase as trees are now growing in areas previously occupied by steppe. Euro–Americans are likely the cause of a reduction in fire activity in watershed since AD 1880.  相似文献   

A comparison of late Quaternary forest changes in New Caledonia and northeastern Australia     

Janelle Stevenson  Geoffrey Hope 《Quaternary Research》2005,64(3):372-383

A pollen record from Lake Xere Wapo, southeast New Caledonia, is the longest continuous terrestrial record to be recovered from the tropical southwest Pacific and reveals a series of millennial scale changes in vegetation over the last 130,000 yr. A comparison of the Lake Xere Wapo record with the key northeast Australian record of Lynch's Crater reveals regional patterns of change. From 120,000 to 50,000 yr ago the vegetation around Lake Xere Wapo alternated between rainforest and maquis with fire an important disturbance factor. In the last 50,000 yr fire is almost absent from the record and the vegetation assumes a character unprecedented in the preceding 100,000 yr, dominated by Dacrydium and Podocarpus pollen. The most compelling aspect of the comparison with Lynch's Crater is that the much-discussed Araucaria decline at around 45,000 yr ago in northern Queensland is matched by a similar decline in the Lake Xere Wapo record.  相似文献   

神农架北坡表土常见花粉的R值研究   总被引：14，自引：4，他引：14  

刘会平  唐晓春  王开发  潘安定 《地理科学》2001,21(4):378-380

根据表土孢粉分析和植被样方调查的比较研究，获得了神农架北坡表土常见花粉的R值，常绿阔叶树花粉一般具有较低代表性，R值变化于0．70左右，绝大部分落叶阔叶树花粉也具有较低代表性，R值变化于0．68－0．88之间，但桦，桤木和槭却表现异常，针叶树有气囊花粉具有明显的超代表性，R值变化在1．35－2．44之间，松表现最为强烈，草本植物花粉的R值变化较大，代表性较差，影响R值的因素很多，植物的生态特性，花粉特征，花粉源距离，花粉产量，地形等作用尤为明显。  相似文献   

乌鲁木齐河下游地区30Ka BP以来湖泊沉积的孢粉组合与古植被古气候   总被引：3，自引：1，他引：3  

李志忠  海鹰  周勇  罗若愚  张秋菊 《干旱区地理》2001,24(3):201-205

根据乌鲁木齐阿尾闾东道海子沉积的孢粉分析，以藜科、蒿属花粉的绝对含量和相对比值确定古植被类型，重建下游平原30Ka BP以来的古气候演变过程。表明末次冰期北疆山麓地带的相对冷湿环境，在本区孢粉组合中也有一定显示；全新世大暖期山前平原地区湖泊来水量增加，湖泊周边湿地沼泽遍布；最近500年来的植被变化与区域气候环境的干暖化趋势有关；而近100年来的植被退化、环境劣变主要是人类自身行为所致。  相似文献   

Late Holocene local vegetation dynamics in the marsh of Gravgaz(southwest Turkey)     

Marleen Vermoere  Thijs Van Thuyne  Simon Six  Leo Vanhecke  Marc Waelkens  Etienne Paulissen  Erik Smets 《Journal of Paleolimnology》2002,27(4):429-451

Late Holocene local vegetation succession is reconstructed in twodifferent sites in a small-scale open marsh ecosystem in southwest Turkey.This is done by comparison of the fossil local pollen assemblage zones in twocores with the local pollen data of 40 surface samples from the marsh. Thepollen data are supplemented with sedimentological and archaeological data. Theinsertion of the mean pollen data of the local pollen zones as passive samplesinto the canonical correspondence analysis triplot of the modern samples allowsus to detect modern analogues for the fossil pollen zones. From this numericalcomparative approach it is concluded that the marsh area was relatively dryuntil ca 2500 BP. After 2500 BP the area shifts towards a wet area dominated bySparganium and/or Typha angustifolia. A diversification of the marsh vegetationstarts at ca 2400/2300 BP. The area around one core site seems to have beensituated in an area with slowly flowing source water, whereas the other coresite is likely to have been characterised by damp conditions. The steadilyincreasing dryness of the marsh area starts after ca 680 BP. The drying upappears to be associated with recent agricultural and grazing pressure.  相似文献   

四川西昌螺髻山全新世植被与环境变化   总被引：15，自引：0，他引：15  

李旭  刘金陵 《地理学报》1988,(1)

通过对沉积物进行孢粉、植物碎屑、硅藻和矿物等的研究和表土的孢粉分析,发现外来孢粉可以远远多于原地沉积的孢粉。并证明该地区在12400年B.P.时,雪线已经高于3660m,从12000年B.P.开始进入全新世。作者在文献[1]中探讨了我国大气透明度系数的空间分布及其主要影响因子。本文则探讨大气透明度系数的时间变化,特别是它的长期变化及其成因。结果发现:火山爆发可使大气透明度系数明显减小;由于人类活动影响,冬季大气透明度系数P_z、P_d有明显的减小趋势,P_2、F_d与用煤量等污染指标有很好的负相关。文中还对大气可降水含量的气候学推算方法进行了探讨。  相似文献   

Terrestrial – Ocean environmental change in the northwestern Pacific from the glacial times to Holocene     

Hodaka Kawahata  Hideaki Ohshima  Azumi Kuroyanagi 《Journal of Asian Earth Sciences》2011,40(6):430-1202

The Mixed Water Region (MWR) between the Oyashio Current and the Kuroshio Extension and surrounding terrestrial region have been affected by the global climatic change. The sedimentary core KR02-15 PC6 collected at 40°23.8871′N, 143°29.8663′E in the MWR provides detailed records of pollen and spores and alkenone sea surface temperature (SST) during the last 15 kyr, showing that both ocean and terrestrial environments have been appreciably linked. Abundance of Picea, a proxy for terrestrial cool climate, fluctuated, coinciding with the alkenone-SST change during the interstadial period (15.0–7.7 cal kyr B.P.). Alkenone-SST increased to the modern level at 8.0 cal kyr B.P. and remained almost constant until 2.0 kyr B.P. while the terrestrial warming still continued until 4.0 cal kyr B.P. The rainfall under terrestrial warm condition increased gradually from 7.9 cal kyr B.P. and rapidly from 2.0 cal kyr B.P. Both terrestrial and marine environments cooled down during the last 2 kyr possibly due to the intensified cold Oyashio Current.  相似文献   

Testing the reliability of pollen-based diversity estimates   总被引：2，自引：2，他引：0  

Matthew Charles Peros  Konrad Gajewski 《Journal of Paleolimnology》2008,40(1):357-368

Rarefaction analysis is a common tool for estimating pollen richness. Using modern and fossil pollen data from the Canadian Arctic and Greenland, we examine the effects of pollen concentration (grains/cc) and evenness (the distribution of species abundances) on palynological richness. Our results show that pollen richness and concentration have a strong negative correlation at low pollen concentrations. There is a positive correlation between pollen evenness and richness, although the strength of this relationship is difficult to determine. Rarefaction analysis on samples of low concentration or high evenness is likely to lead to pollen richness being less underestimated than on samples of high concentration or low evenness. These findings corroborate theoretical research on these issues.  相似文献   

川西安宁河Ⅰ～Ⅲ级阶地孢粉记录反映晚更新世以来古气候变化          下载免费PDF全文

程建武  宫会玲  郭雪莲 《地震工程学报》2010,32(4):349-356

植物孢子和花粉是理想的恢复环境变化的有机指标,对于第四纪地层划分和区域古气候的对比具有重要意义。本文在川西冕宁泸沽镇附近选取安宁河Ⅰ～Ⅲ级阶地剖面进行年代学测量和孢粉采样分析。结果表明:安宁河Ⅰ级阶形成时期为全新世,气候温和较湿或轻湿;Ⅱ级阶地沉积时期在晚更新世晚期或全新世早期,温度及湿度均比Ⅰ级阶地时低,在该时期无论植被和气候曾出现过两次以上比较明显的变化及波动;Ⅲ级阶地沉积时期为晚更新世中期,气候温和较湿或轻湿,堆积时期之温度及湿度均比Ⅱ级阶地时高,但又均比Ⅰ级阶地时低。同时探讨了安宁河阶地形成时期构造、气候的变化规律。根据河流的下切速率可以间接的推断晚更新世构造隆升速率大于晚更新世末期-全新世。  相似文献