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A proxy climate record from a raised bog in County Fermanagh, Northern Ireland, is presented. The record spans the interval between 2850 cal. yr BC and cal. yr AD 1000 and chronological control is achieved through the use of tephrochronology and 14C dating, including a wiggle‐match on one section of the record. Palaeoclimatic inferences are based on a combination of a testate amoebae‐derived water table reconstruction, peat humification and plant macrofossil analyses. This multiproxy approach enables proxy‐specific effects to be identified. Major wet shifts are registered in the proxies at ca. 1510 cal. yr BC, 750 cal. yr BC and cal. yr AD 470. Smaller magnitude shifts to wetter conditions are also recorded at ca. 380 cal. yr BC, 150 cal. yr BC, cal. yr AD 180, and cal. yr AD 690. It is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest Europe. Harmonic analysis of the proxies illustrates statistically significant periodicities of 580, 423–373, 307 and 265 years that may be related to wider Holocene climate cycles. This paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing. Relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China 总被引：15，自引：0，他引：15
J. A. Holmes 《中国科学D辑(英文版)》2006,49(12):1280-1290
Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating re- sults. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000―1500 AD, a humid climate during the Little Ice Age (LIA) (c. 1500―1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indi- cate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concen- trations, decreased carbonate content and increased grain size. The humid period during the LIA re- corded by the Bosten Lake sediments is representative of arid central Asia and is supported by nu- merous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipita- tion increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA. 相似文献
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Pollen data are well established for quantitative climate reconstructions over long timescales, including the Holocene and older interglacials. However, anthropogenically induced environmental change in central Europe was strong during the last 4 ka, challenging quantitative reconstructions of this time period. Here we present quantitative climate reconstructions based on pollen analyses and evaluate them with the peat humification record and the stable carbon isotopes of Sphagnum plant material (δ13Ccellulose). All analyses were carried out on the same 7.5 m long, largely ombrotrophic peat bog section from Dürres Maar. Three different methods were used for the quantitative climate reconstructions on the basis of the pollen data: (1) a probabilistic indicator taxa approach (the ‘pdf method’); (2) a modern analogue technique based on pollen taxa from modern surface samples (cMAT); and (3) a modern analogue technique expanded by plant functional types (pMAT). At Dürres Maar the peat humification is only affected by peat cutting during the Roman period and the Middle Ages. The stable carbon isotopes are seemingly unaffected by human impact. Thus both proxies provide independent data to evaluate the reconstructions on the basis of pollen data. The quantitative climate reconstructions on the basis of the individual methods are in general relatively similar. Nevertheless, distinct differences between the individual approaches are also apparent, which could be attributed to taxa that reflect human impact on a local to regional scale. While the pdf method appears to be relatively robust to all observed anthropogenically induced vegetation changes, it potentially underestimates climate variability. This method is therefore expected to be independent of local site characteristics and to provide robust quantitative estimates of climatic trends rather than of climatic variability of small amplitude. This is of value for palaeoclimate reconstructions of older interglacials, for which neither multiple sites nor independent climate proxies are available for comparison. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Two new peat‐based climate records from Ireland covering the late Holocene are presented. The sequences are dated by a strong chronological framework formed by AMS radiocarbon dates and SCPs. Three proxy indicators (testate amoebae, macrofossils and humification) have been determined allowing the limitations and strengths of each to be identified and utilised to provide a bog surface wetness (BSW) record for both sites. Age–depth models take into account the potential for accumulation rates to vary with bog vegetation. The records from each site have been used to derive a combined BSW record that displays changes to a wetter/cooler climate from ca. AD 30 (1920 BP), ca. AD 310 (1640 BP), ca. AD 805 (1145 BP), ca. AD 1040 (910 BP) and ca. AD 1300 (650 BP). Changes follow closely those identified in a northern Britain composite BSW record and largely correspond with lake‐level data in central France suggesting the main changes in water balance were coherent over a large region. Correspondence with increases in IRD and slower Iceland‐Scotland Overflow Water (ISOW) suggests that these changes were related to oceanic forcing influencing the track of dominant westerly air flow over Ireland. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Francesca Sangiorgi Lucilla Capotondi Nathalie Combourieu Nebout Luigi Vigliotti Henk Brinkhuis Simona Giunta Andr F. Lotter Caterina Morigi Alessandra Negri Gert‐Jan Reichart 《第四纪科学杂志》2003,18(8):723-732
Holocene cooling events have been reconstructed for the southern Adriatic Sea (central Mediterranean) by means of analyses of organic walled dinoflagellate cysts, planktonic foraminifera, oxygen isotopes, calcareous nanoplankton, alkenones and pollen from a sediment core. Two cooling events have been detected, during which sea‐surface temperatures (SSTs) were ca. 2°C lower. Unravelling the SST signal into dominant seasonal components suggests maximum winter cooling of 2°C at around 6.0 ka, whereas the cooling at ca. 3.0 ka might be the result of a spring temperature cooling of 2–3°C. The events, lasting several hundred years, are apparently synchronous with those in the Aegean Sea, where they have been related to known cooling events from the Greenland ice‐core record. A distinct interruption in Adriatic Sea sapropel S1 is not clearly accompanied by a local drop in winter temperatures, but seems to be forced by ventilation, which probably occurred earlier in the Aegean Sea and was subsequently transmitted to the Adriatic Sea. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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C. Gregory Skilbeck Timothy C. Rolph Natalie Hill Jonathan Woods Roy H. Wilkens 《第四纪科学杂志》2005,20(4):327-347
We have undertaken a comparative study of down‐core variation in multiproxy palaeoclimate data (magnetic susceptibility, calcium carbonate content and total organic carbon) from two coastal water bodies (Myall and Tuggerah Lakes) in temperate eastern Australia to identify local, regional and global‐forcing factors within Holocene estuarine sediments. The two lakes lie within the same temperate climate zone adjacent to the Tasman Sea, but are not part of the same catchment and drain different geological provinces. One is essentially a freshwater coastal lake whereas the other is a brackish back‐barrier lagoon. Despite these differences, data from two sites in each of the two lakes have allowed us to investigate and compare cyclicity in otherwise uniform, single facies sediments within the frequency range of 200–2000 years, limited by the sedimentation rate within the lakes and our sample requirements. We have auto‐ and cross‐correlated strong periodicities at ～360 years, ～500–530 years, ～270–290 years, 420–450 years and ～210 years, and subordinate periods of ～650 years, 1200–1400 years and ～1800 years. Our thesis is that climate is the only regionally available mechanism available to control common millennial and centennial scale cyclicity in these sediments, given the geographical and other differences. However, regional climate may not be the dominant effect at any single time and either location. Within the range of frequency spectral peaks we have identified, several fall within known long‐term periodical fluctuations of sun spot activity; however, feedback loops associated with short‐term orbital variation, such as Dansgaard–Oeschger cycles, and the relationship between these and palaeo‐ENSO variation, are also possible contributors. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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通过对狮子潭柱状沉积物的放射性定年、地球化学与硅藻分析,反演桂林会仙岩溶湿地全新世的古湖沼演替,与其响应的气候变迁与人类活动记录。放射性210Pb、14C定年结果显示该湖在6 400 cal BP开始有湖积物保存,在2 700 cal BP—公元1943年间有沉积间断事件,且于公元1943年再度沉积。在6400—5 200 cal BP,高比例的浮游型硅藻反映高水位状态,可对应到气候暖湿的中国全新世大暖期鼎盛期。在5 200—2 700 cal BP,沉积物内稀酸可溶相Ca、Mg、Sr浓度降低,Mg/Ca、Sr/Ca值明显增加,且浮游型硅藻几乎消失,显示当时湖泊水位显著降低,气候逐渐变干。在公元1943年沉积物再度沉积,可能与战争造成人口迁徙与废耕有关。自公元1973年以来,硅藻壳片大量堆积,反映人类过度活动造成藻华的现象。湖泊沉积物内硅藻组成及沉积物的地球化学特征能够很好地反演古气候、环境变迁。 相似文献
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