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Medieval Warm Period (medieval + warm_period)
Selected AbstractsA Rb/Sr record of catchment weathering response to Holocene climate change in Inner MongoliaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2006Zhangdong Jin Abstract Variation in the rubidium to strontium (Rb/Sr) ratio of the loess,palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of China. To characterize the Rb/Sr ratio of the dissolved loads of a single catchment, we analysed a 12·08 m sediment core from Daihai Lake in Inner Mongolia, north China. Dating control was provided by 210Pb, 137Cs and AMS- 14C. Sequential extraction experiments were conducted to investigate the concentrations of Rb and Sr on various chemical fractions in the lake sediments. Down-core variation in the Rb/Sr ratios provides a record of Holocene weathering history. From 9 to 3·5 ka bp, accelerated chemical weathering was experienced throughout the Daihai catchment under mainly warm and humid conditions, and this reached a maximum at c. 5 ka bp. However, weathering was reduced between c. 8·25 and 7·90 ka bp, which may reflect the global 8·2 ka cooling event. After c. 2·5 ka bp, increased Rb/Sr ratios with higher frequency of fluctuations indicate reduced weathering within the Daihai catchment. The highest Rb/Sr ratios in the Little Ice Age lake sediments indicate the weakest phase of Holocene chemical weathering, resulting from a marked reduction in Sr flux into the basin. The Rb/Sr record also shows an enhancement of chemical weathering under today's climate, but its intensity is less than that of the Medieval Warm Period. Increased Rb/Sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to Rb/Sr decrease in the glacial loess layers in the loess,palaeosol sequence. Copyright © 2005 John Wiley & Sons, Ltd. [source] TEMPERATURE PROXY RECORDS COVERING THE LAST TWO MILLENNIA: A TABULAR AND VISUAL OVERVIEWGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2009FREDRIK CHARPENTIER LJUNGQVIST ABSTRACT. Proxy data are our only source of knowledge of temperature variability in the period prior to instrumental temperature measurements. Until recently, very few quantitative palaeotemperature records extended back a millennium or more, but the number is now increasing. Here, the first systematic survey is presented, with graphic representations, of most quantitative temperature proxy data records covering the last two millennia that have been published in the peer-reviewed literature. In total, 71 series are presented together with basic essential information on each record. This overview will hopefully assist future palaeoclimatic research by facilitating an orientation among available palaeotemperature records and thus reduce the risk of missing less well-known proxy series. The records show an amplitude between maximum and minimum temperatures during the past two millennia on centennial timescales ranging from c. 0.5 to 4°C and averaging c. 1.5,2°C for both high and low latitudes, although these variations are not always occurring synchronous. Both the Medieval Warm Period, the Little Ice Age and the 20th century warming are clearly visible in most records, whereas the Roman Warm Period and the Dark Age Cold Period are less clearly discernible. [source] A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central FinlandBOREAS, Issue 4 2003MIA TILJANDER High-resolution physical analyses (varve thickness and relative X-ray density) were conducted on a 3000-year varved sediment sequence in Lake Korttajarvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajarvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980,1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30-year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580,1630 and AD 1650,1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c. 2800 years ago. [source] Late Holocene environmental change in Disko Bugt, west Greenland: interaction between climate, ocean circulation and Jakobshavn IsbraeBOREAS, Issue 1 2006JEREMY M. LLOYD Foraminiferal assemblages and the sedimentology of two cores (POR20 and POR21) from eastern Disko Bugt, west Greenland, are used to identify environmental changes in the area over the past c. 2200 years. Changes in the sediment flux supplied to the core sites from Jakobshavn Isbrae are used to assess the relative position of the calving margin. An Atlantic water influence as strong as, or slightly stronger than, present prevailed at c. 2200 cal. yr BP. A trend of increasing Atlantic water influence then culminated in peak warm and saline hydrographic conditions c. 1664,474 cal. yr BP encompassing the ,Medieval Warm Period'. This period was marked by a retreat of the calving front of Jakobshavn Isbrae and was followed by a marked cooling in hydrographic conditions relating to an increase in the influence of the East Greenland Current in the West Greenland Current corresponding to the climatic episode the ,Little Ice Age'. A rise in sedimentation rate over this period relates to the well-documented advance of Jakobshavn Isbrae. The record from Disko Bugt shows good agreement with the temperature record from the Greenland ice cores and other climatic and oceanographic reconstructions in the region. [source] | ||||||||||