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1.
Despite extensive AMS-14C dating series on Late-glacial terrestrial plant remains, a precise estimate of the duration of the Younger Dryas biozone (sensu Ammann & Lotter, 1989) is hampered by the occurrence of a period of constant 14C-age at 10 000 yr B.P. However, varve counts at Soppensee suggest that the Younger Dryas biozone comprises approx. 680–720 varves, and that the phase of constant radiocarbon age includes between 270–310 varves.  相似文献   
2.
Upper Mustang is a land of extraordinary, precious, tangible and intangible cultural heritage deeply rooted in the Tibetan culture and tradition of Buddhism as well as the Bön religion. The unique architecture provides a great source of timber suitable for dendrochronological research. Century-old fortresses, palaces, Buddhist monasteries and temples, houses and chörtens reflect the great importance of wood as a building material (used alongside clay and stone). We present pioneering research on historical wood from Upper Mustang. The objectives of the study were to determine the wood species used in the traditional architecture of the region, to make an attempt to date materials from Upper Mustang using existing tree-ring chronologies developed for neighbouring geographical regions and to determine the need and the chance of creating separate tree-ring chronologies for Upper Mustang. For the presented study we collected 191 samples from the oldest buildings preserved in Upper Mustang. Anatomical studies of samples resulted in the identification of four species of conifer wood: Himalayan pine – Pinus wallichiana A.B. Jacks, Himalayan fir – Abies spectabilis D.Don, Juniperus spp. and Larix spp. The main achievement of our research was the development of an Upper Mustang master chronology covering the period from 1317 to 1943. The chronology is based on data derived from Pinus wallichiana A.B. Jacks.  相似文献   
3.
千山油松年轮宽度年表的建立及其与气候的关系   总被引:5,自引:0,他引:5  
以千山油松为样本,建立了年轮宽度标准化年表、差值年表和自回归年表.结果表明,油松年轮宽度与5—7和9—11月温度指标的相关性较高,且与低温呈正相关,其中与7月的极端最低温、9月的平均最低温显著相关.3种年表与上年12月和当年1月的极端最低温、1月的平均最低温呈显著相关,且其与全年、上年12月、当年5月的降水量显著相关,与4月的降水量极显著相关.油松与水汽压、相对湿度的月和年指标均有较强的相关性.蒸发的年指标和绝大部分月指标对油松生长具有负效应,其中4—7月最明显.油松年表的窄化突变佐证了1800年以来的30次主要的旱灾年历史记录.千山油松的生长受全球或半球尺度气候变化的影响.年表与太阳活动存在显著的11、23和50年左右的公共周期,与地磁指标在10、20和45年左右存在共同的周期变化.  相似文献   
4.
Sediment cores were collected from lakes in central and northern Canada and from Hudson Bay to compare current and historic net depositions of mercury. Cores from most locations were enriched in mercury in the upper layers deposited recently relative to deeper, historic layers. The lakes with the greatest enrichments in mercury were located in central/southern Canada. This enrichment was interpreted as being of anthropogenic origin. Mercury inputs at the Experimental Lakes Area (ELA) in northwestern Ontario inferred from a core profile agreed well with inputs calculated independently from precipitation and runoff data. Anthropogenic inputs of mercury to northwestern Ontario were calculated to be about 9 µg m-2 y-1. Considering all the locations over the geographic range, the core profiles infer that fluxes of mercury have increased on average by about 2 fold over the past half century. This is consistent with results from other sites in North America and Europe.  相似文献   
5.
神农架地区米心水青冈萌枝更新过程的研究   总被引:2,自引:1,他引:1       下载免费PDF全文
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6.
In 1992, we discovered populations of the nonindigenous quagga mussel Dreissena rostriformis bugensis in the middle reaches of the Volga River. The same species was found in samples collected between 1994 and 1997 in the Volga delta and in shallow areas of the Northern Caspian Sea. D. r. bugensis always co-occurred with its more widespread congener, the zebra mussel D. polymorpha (Pallas 1771). The quagga mussel's contribution to total Dreissena abundance increased over time in the middle Volga reservoirs and Volga River delta. D. r. bugensis was common in the Volga portion of Rybinsk Reservoir during 1997 and, by 2000, it was in Uglich, Rybinsk and Gorky Reservoirs on the Upper Volga River. D. r. bugensis was neither found in Ivankov Reservoir, nor in terminal sections of the Volga-Baltic corridor including the eastern Gulf of Finland. Presently, all but the northern-most regions of the Volga River have been colonized by D. r. bugensis. We hypothesize that its introduction into the Volga River and Caspian basin occurred no later than the late 1980s via commercial shipping that utilized the Volga-Don waterway to navigate between the source Black-Azov Sea region and recipient areas on the Volga River. Larval drift likely contributed to establishment of populations at downstream sites, while human-mediated vectors may be responsible for introductions to upstream locations on the Volga River. We anticipate continued northward dispersal in conjunction with shipping activities.  相似文献   
7.
Juvenile mugilid fishes, Liza falcipinnis, L. dumerilii, Mugil bananensis and M. curema , which enter the Elmina Lagoon in the Cape Coast District of Ghana, have a similar diet comprising mainly bacteria, diatoms, blue-green/green algae, protozoans, detritus and particulate organic matter. No seasonal changes in the diet and feeding activity were observed. The relative gut length (intestine to standard length ratio) and diet showed no significant changes with size of fish in all the species. All four species were diurnal feeders, but their peak feeding times differed. Interspecific competition for food was possibly limited by species preferences for substrate particles of particular size range and differences in feeding chronology.  相似文献   
8.
雷帅  张劲松  孟平  何子兵  程顺  孙守家 《生态学报》2020,40(13):4479-4492
通过树木年代学方法,测定了毛乌素和塞罕坝相同密度樟子松(Pinus sylvestris var.mongolica)全木(Ringwood,RW)、早材(Earlywood,EW)和晚材(Latewood,LW)宽度,计算胸高断面积增量(Basal area increment,BAI),并建立了樟子松年轮宽度年表,分析其对气候响应的差异。结果显示,毛乌素(Mu Us)樟子松轮宽随树龄呈"升-降"的曲线变化,塞罕坝(Saihanba)呈线性下降,两地樟子松BAI变化相似,呈"升-降"的曲线变化,EW占RW的65%—70%,表明EW对RW贡献较大。生长期间,毛乌素樟子松早晚材比例保持平稳,塞罕坝EW/RW值下降,LW/RW值上升,两地干旱事件均使LW/RW值下降,EW/RW值上升。差值年表(Residual chronology,RES)相关性分析显示,毛乌素樟子松径向生长主要与4、7月平均降雨,7月标准化降水蒸散发指数(Standardized precipitation evapotranspiration index,SPEI),3、8月平均温度及上年12月和当年3月最低温度呈正相关关系,与上年11月和当年6月最高温度呈负相关关系。塞罕坝樟子松径向生长主要与7、8月平均降雨、SPEI和最低温度呈正相关关系,与当年3、5月最高温度呈负相关关系。结构方程模型表明,毛乌素年平均温度和年SPEI对樟子松RW产生极显著负效应,年平均降雨对RW产生显著正效应,年平均降雨对EW产生极显著正效应,年最低温度和年平均温度分别对LW产生极显著正/负效应。塞罕坝樟子松径向生长对其年气象因子响应与毛乌素相似,但有部分差别,塞罕坝年平均降雨对LW产生极显著负效应,但对EW未达到显著性水平,且年SPEI对塞罕坝樟子松RW和EW产生的干旱胁迫效应明显小于毛乌素。  相似文献   
9.
辽宁省人工林樟子松径向生长对水热梯度变化的响应   总被引:3,自引:0,他引:3  
基于树轮年代学的理论和方法,建立辽宁地区人工林樟子松年轮宽度年表网络,研究人工林樟子松树木年轮生长变化,探讨樟子松生长与气候变化的关系以及其对水热梯度变化的响应规律。结果表明,研究区各采样点人工林樟子松的径向生长变化呈现较为一致的显著下降趋势(P0.05),并且下降趋势由西北至东南降低。空间上水平上,研究区樟子松的径向生长与研究区降水和相对湿度的空间梯度变化吻合(P0.05),均呈西北至东南增加的特点;各采样点樟子松年轮宽度变化的平均敏感度与降水量、相对湿度显著负相关关系(P0.05),但与温度的正相关关系不显著。各样点樟子松径向生长与月降雨量和月平均相对湿度多呈正相关关系,与月平均温度多呈负相关关系,进一步表明区域水分因子对人工林樟子松生长的限制作用明显。  相似文献   
10.
Breeding chronology, harem structure and changes in male harem dominance were studied at Stranger Point, Isla 25 de Mayo/King George Island, principally by extensive field census work during the 2003 breeding season. Males were individually identified and their size estimated by using a photogrammetric method. Peak female haul out for the population occurred on 31 October, when a total of 276 females were observed along 7 km of coastline, distributed in ten harems with a median size of 16 females. Overall sex ratio and harem sex ratio for the breeding population were 1:6.7 and 1:10.6, respectively. A total of 33 males were identified associated with harems. Male size conferred an advantage in terms of dominance hierarchy, since dominant males (4.91±0.15 m) were significantly longer than subordinate males (4.63±0.19 m). Harems were dominated by an average of 4.5 (range 2–7) different males during the breeding season. Elephant seals at Stranger Point breed in very low density aggregations. The main breeding events in this population occurred later than at other breeding sites, which agrees with previous observations in the area. Male movement among harems suggests that differences in mating success among males could be achieved through their different behaviours.  相似文献   
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