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This Special Issue of The Holocene contains 16 research papers based on a symposium at the 11th International Meeting of the European Union of Geosciences held in Strasbourg in April 2001. The aim of the symposium was a state-of-the-art assessment of empirical studies of postglacial marine and terrestrial climatic archives and their integration with numerical climate models. This editorial places the individual papers in the broader context of natural climate variability and anthropogenic impacts on the global climate system, regional differences in climate between maritime and continental areas, and the need for an improved theoretical basis for understanding the underlying causes of environmental change. The focus of the Special Issue is the dynamic and relatively well-understood climate of the North Atlantic and the European realm, where, in relation to the steepest offshore temperature gradient on Earth, observational data are abundant and many recent advances have been made in climate reconstruction from proxy archives. The editorial also contains a summary and overview of the papers included in the four main sections of the Special Issue, which emphasize: (1) numerical modelling experiments; (2) models of glacier buildup and equilibrium-line altitude; (3) marine and terrestrial proxy records of climatic change; and (4) multiproxy palaeoenvironmental reconstruction of a Portuguese lagoonal system. [ABSTRACT FROM AUTHOR]

This series of papers addresses the principal natural and anthropogenic environmental changes that have transformed a typical lowland Scottish landscape during the Holocene. Sediment- and pollen- stratigraphic techniques, together with radiocarbon dating, are applied in this paper to the stratigraphy of a raised bog at Burnfoothill Moss, eastern Dumfriesshire, to deduce changes in groundwater levels within the bog, and by inference, changes in effective precipitation. The basin, initially a shallow pond, was rapidly colonized by fen peat at 9600 BP, possibly during a phase of drier climate, which ended at c. 8700 BP. Short-lived fluctuations in bog-surface wetness are identified before a major change to a wetter bog surface at around 7700 cal. BP, representing the transformation from fen peat to raised moss. Anthropogenic interference with surrounding woodland is believed to have destabilized the water balance within the peat. Drier bog-surface conditions occur at c. 6700 cal. BP, and a shift to a wetter climate at around 5250 cal. BP, but a perhaps more substantial wet shift is recorded at c. 4000 cal. BP. At c. 1900 cal. BP a dry climate shift is recognized, ending at c. 1200 cal. BP. Slightly prior to the 'Little Ice Age', represented by a very wet phase before c. 400 cal. BP, is a dry period between c. 600 and 400 cal. BP. [ABSTRACT FROM PUBLISHER]

This paper presents evidence for the nature of early and middle Neolithic farming activity, its impact upon the landscape and environment, and its vulnerability to climatic change, at a sub-peat field system at Belderg Beg, North Co. Mayo, Ireland. Pollen analyses of a 14C dated peat deposit close to the field system indicates that basin peat accumulated from c. 5590 to 5330 cal. BP, probably triggered by farming activities. The palynological evidence indicates that the field system was constructed for pastoral farming, surrounded by woodland. Sediment-stratigraphic analyses show that the soil in the field system was subject to significant erosion, which may have been a causal factor in the local cessation of agriculture in the late sixth millennium cal. BP. Peat humification analyses indicate that surface wetness was greatest at c. 4940 cal. BP, several centuries after abandonment of the field system, coincident in age with evidence for higher precipitation from other sites in North Mayo. Comparison with other records of early and mid-Neolithic agricultural activity and abandonment in the region suggests that the well-recognised mid-Neolithic agricultural decline occurred in the broad context of a shift to a more oceanic climate, but that local factors such as soil quality may have been more important in the exact timing of local agricultural abandonment. [ABSTRACT FROM PUBLISHER]

Ice cores from the relatively low-lying ice caps in Svalbard have not been widely exploited in climatic studies owing to uncertainties about the effect of meltwater percolation. However, results from two new Svalbard ice cores, at Lomonosovfonna and Austfonna, have shown that with careful site selection, high-resolution sampling and multiple chemical analyses it is possible to recover ice cores from which part of the annual signals are preserved, despite the considerable meltwater percolation. The new Svalbard ice cores are positioned in different parts of Svalbard and cover the past 800 years. In this paper we focus on the last 400 years. The δ18O signals from the cores are qualitatively similar over most of the twentieth century, suggesting that they record the same atmospheric signal. Prior to AD 1920, the Austfonna ice core exhibits more negative δ18O values than Lomonosovfonna, although there are intermittent decadal-scale periods throughout the record with similar values. We suggest that the differences reflect the effect of the inversion layer during the winter. The pattern in the δ18O records is similar to the Longyearbyen air-temperature record, but on an annual level the correlation is low. The Austfonna record correlates well with the temperature record from the more distant and southwesterly located Jan Mayen. A comparison of the ice-core and sea-ice records from this period suggests that sea-ice extent and Austfonna δ18O are related over the past 400 years. This may reflect the position of the storm tracks and their direct influence on the relatively low-altitude Austfonna. Lomonosovfonna may be less sensitive to such changes and primarily record free atmospheric changes instead of variations in sea-ice extent, the latter is probably a result of its higher elevation. [ABSTRACT FROM AUTHOR]

The focus of this paper is on the reconstruction of the mid-Holocene climatic changes based on the pollen records contained in a 6.2 m thick section in the southern part of the Tengger Desert, northwestern China. To understand the modern analogues of the mid-Holocene changes, modern pollen spectra across different vegetation zones from the Qilian Mountains to the lowland Tengger Desert were studied first. Four pollen combinations were identified, corresponding to four different modern ecological environments: (1) a Picea-Artemisia combination in a spruce forest and its vicinity; (2) an Artemisia-Chenopodiaceae-Gramineae-Salix combination in a mixture belt of montane grassland and poplar woodland; (3) a Chenopodiaceae-Artemisia-Nitraria combination in a desert steppe belt; and (4) an Elaeagnus-Artemisia-Chenopodiaceae-Nitraria combination in a desert riparian forest. Our study also shows that a relatively low percentage of Picea pollen (30–10%) seems to be associated with water transportation (alluvial deposits) and a very low percentage of Picea pollen (10–5%) appears to be related to long-distance air transportation. With references to the modern relationships between pollen assemblages and associated bioclimates, the pollen sequence covering the period between 8500 and 3000 cal. BP was used to infer the climatic change history. The results show that a warmer and drier climate dominated between 8500 and 7950 cal. BP. Subsequent decreases in Artemisia and warm desert forbs/shrubs taxa and contemporaneous fluctuating increases in montane coniferous and aquatics elements from 7950 to 7400 cal. BP reflect a fluctuating increase in humidity and/or a fluctuating decrease in temperature. The following period from 7400 to 5650 cal. BP was generally warm with the Holocene Climate Optimum occurring between 7400 and 6500 cal. BP. A remarkably cool spell followed between 6500 and 6300 cal. BP that was then succeeded by a warmer and more humid period between 6300 and 5650 cal. BP. The period between 5650 and 4450 cal. BP was characterized by drastic oscillations in climatic conditions with three humid and probably cold spells intervened by three relatively dry and warm spells. The period between 4450 and 3500 cal. BP was cold and humid, followed by a wet spell as indicated by a very high percentage of Typha pollen. [ABSTRACT FROM AUTHOR]

Two cores of mid-Holocene raised-hog deposits from the Netherlands were [SUP14]C wiggle-match dated at high precision. Changes in local moisture conditions were inferred from the changing species composition of consecutive series of macrofossil samples Several wet-shifts were inferred, and these were often coeval with major rises in the Δ[SUP14]C archive (probably caused by major declines in solar activity). The use of Δ[SUP14]C as a proxy for changes in solar activity is validated. This paper adds to the increasing body of evidence that solar variability forced climatic changes during the Holocene. [ABSTRACT FROM AUTHOR]

Peatlands provide a widespread terrestrial archive of Holocene environmental change. The taphonomy of peat is relatively simple, the range of evidence and proxies is wide, and dating methods have become more accurate and precise, such that the potential temporal resolution of records is high. Although long established the use of peatlands as archives of Holocene change has undergone phases of decline and resurgence. Here the variable exploitation of the peat archive is explored and recent developments in peatland science as applied to Holocene records are reviewed with reference to the collection of papers in this Special Issue of The Holocene, which are arranged in four key themes: (1) records of Holocene climatic change: (2) peatland dynamics: (3) carbon accumulation: and (4) implications for conservation and management. The changing acceptance of peatlands as archives of Holocene climatic change is attributed to developments in understanding of the peatland system and geographical differences in the history of Holocene research. Recent developments in biological and geochemical proxies combined with improvements in chronological techniques have resulted in renewed interest in peatland palaeoclimate records. Peatlands are an important global carbon pool and it is clear that climate has influenced the efficiency of long-term carbon sequestration by these systems. Climate has also had an impact on the biodiversity and condition of peatlands, which creates problems in discerning cause and effect in sites affected by human activities, and in targeting remedial management. It is concluded that particular strengths of the archive are the current diversity of peat-based palaeoenvironmental research and the potential for multiproxy analyses to he applied to a range of research issues. Mire-based investigations can complement research in other realms, and are deserving of greater attention from researchers of other archives. [ABSTRACT FROM AUTHOR]

This paper examines the mid- to late-Holocene (c. 6850-1160 cal. yr BP) environmental history of Sierra de Gádor in southern Spain. The local vegetation dynamics are reconstructed through the palaeoecological record obtained from a lacustrine deposit situated at 1530 m. Various hypotheses are considered to explain the vegetation dynamics apparent in the palaeoecological evidence, including climatic change, fire occurrence and human activity. Although the vegetation in this region is sensitive to climatic change, threshold events driven by ecological factors are also apparent. Climatic events include a thermo-mesophytic optimum with abundance of deciduous trees and maximum lake water level found from c. 6850 to 5500 cal. yr BP. In contrast, changes in the frequency of major fire episodes appear to have shaped interspecific relationships and vegetation change, especially from c. 4200 cal. yr BP onwards. Biotic properties of the ecosystem such as the inertia of established tree populations, interconnected with competition adjustments, appear also to have played a role. Over the last two millennia, overgrazing, combined with natural and/or human-set fires, appears to have pushed mountain forests over a threshold leading to the spread of grassland, thorny scrub, junipers and nitrophilous communities. [ABSTRACT FROM AUTHOR]

This paper reviews the development of the current 'supra-long' pine chronology for northern Finnish Lapland. In the forest-tundra ecotone region of northern Finnish Lapland over 250 samples from living Scots pines (Pinus sylvestris L.) and over 1700 samples of subfossil pines have been collected for dendrochronological studies. In addition, over 1400 subfossils have been sampled from the forested area of Finnish Lapland. The goal of the research was to build a more than 7000-year long continuous pine ring-width chronology. The construction of the chronology is now completed. The intensive phase of the data collection and chronology building lasted about 10 years, 1989 to 1999. The major part of the Finnish Lapland master curve was constructed several years ago, but it was extremely difficult to bridge the c. 300-year gap, prior to 165 BC between the 'absolute' younger part of the chronology and the 'floating' older part. The crucial samples were identified and assembled in the chronology in early 1999, and there is now an unbroken pine chronology about 7500 years long constructed from the subfossil forest-limit pines of northern Finnish Lapland. The severe growth depression centred on 330 BC is likely to have been caused by increased wetness. A brief summary is presented of inferred tree-line changes from the location of the samples. [ABSTRACT FROM AUTHOR]

The primary aim of this paper is to describe and discuss the palaeoclimatic significance of mid- to late-Holocene fields of raised-beach ridges at Matalaniemi and sea-ice-pushed boulders at Kutovaya Bay on the Kola Peninsula. These beach features are interpreted as indicating at least 12 periods of stormy conditions alternating with calmer periods of relatively low sea-surface temperature since about 8000 cal. BP. A consistent chronology of climate change is difficult to establish due to considerable uncertainties attributed to local beach processes and relative sea-level displacements. A tentative interpolated chronology is suggested. At present, terrace formation at Matalaniemi and the absence of sea ice at Kutovaya Bay indicate an intermediate windy and mild type of winter climate. [ABSTRACT FROM AUTHOR]

A combined geomorphological, radiocarbon dating, archaeological and historical approach permits a refining of the age of the coastal dune systems related to estuaries in the Gulf of Cádiz. Three dune systems are distinguished in this paper. The oldest one, D1, which accumulated under prevailing WSW winds during the first millennium bc, overlays both the occupational horizons of Late Neolithic-Early Copper Age (fourth millennium bc) and the ‘lithic workshop levels’ (fourth to second millennia bc). The middle dune system, D2, containing both Roman and medieval remains, accumulated between the thirteenth or fourteenth centuries and the seventeenth century ad. The youngest D3 system is associated with the time of building of watchtowers in the seventeenth century ad but extends to the present; it is related to SW prevailing winds. We explain the absence of aeolian deposits prior to ~2700 cal. BP as the result of trapping of a large part of the sediment supply in the estuaries, which starved the neighbouring beaches and aeolian settings. Aeolian accumulation reached significant values when sedimentation in the coastal zone changed from being mainly aggradational in the estuaries (~6500–2700 cal. BP) to mainly progradational in spit barriers and related dunes (post ~2700 cal. BP). The present analysis of aeolian systems suggests a non-direct correlation, at least in some cases, between coastal progradation of spit barriers and aridity. [ABSTRACT FROM AUTHOR]

This paper reports on the paludification of kettle holes formed in a proglacial esker complex at Lake Bienville in northern Qubec. Deep hollows on the central islands of this large subarctic lake (c. 900 km2, are highly exposed to northeasterly and southwesterly winds over long fetches, and accumulate large amounts of drifting snow (c. 4m). Modifications in local snow distribution associated with Holocene vegetation and climate changes contributed to an increased water supply in kettle holes. Podzolic soils with light patches in the B horizon are attributed to differential water circulation during thawing in coarse-textured soils with high moisture supply associated with thicker snow. Peat started to form over well-drained podzolic soils and paludification of kettle holes are interpreted as the result of a combination of bioclimatic events including: (1) the development of a postfire, open-vegetation cover after c. 1500 BP associated with cooler conditions exacerbated by the presence of a large water body; and (2) the shift from a boreal- to a subarctic-like (wind-controlled) snow regime permitting the accumulation of large amounts of snow and late melting. [ABSTRACT FROM AUTHOR]

The focus of this study is the possible correlation between changes in the climate of Scandinavian and changes in solar irradiation. Reliable information about Holocene climatic change in Sweden and Norway is currently available from two main sources: the 14C dating of pine wood retrieved from above the present pine-tree limit and studies of glacier variations based on proglacial lacustrine sediments and on moraines. The reconstructed alpine tree-limit reveals that summer temperature in general was warmer during the early Holo cene than it was during the late Holocene. Superimposed on this general trend are several fluctuations of a few hundred years' duration. Relatively cold periods with a duration of the order of 300-600 years occurred frequently during the Holocene. In this paper, dates of the major climatic events are compared with an index of solar activity, the so-called δ14C anomalies. For most of the last 9000 years a good correspondence is demonstrated between the timing of cold events in Scandinavia and the timing of major δ14 C anomalies (low solar irradiation). The general Holocene cooling trend is believed to be partly a result of land uplift following deglaciation and partly a result of orbitally forced changes in irradiation. Large fluctuations in Scandinavian summer temperature can be reconciled with the pattern of climatic change presented in several recent studies in the North Atlantic region. A link between these areas could be provided by changes in the production of North Atlantic Deep Water. [ABSTRACT FROM PUBLISHER]

The extensive coniferous forests of the western Himalayas provide great potential for dendroclimatic research. Abies, Cedrus, Picea and Pinus are the main tree genera of the region, consisting of many old and living trees. The annual growth-ring patterns of these trees, which can be precisely dated, contain valuable high-resolution information on climate variability over the past few centuries. This paper presents an analysis of the ring-width data of Abies pindrow and Picea smithiana based on samples collected from forest sites around Pahalgam in the Kashmir Valley in 1982. The non- climatic variations have been filtered out of the raw ring-width series using a cubic spline smoothing, and ring-width index series have been obtained. The mean ring-width index chronologies have been prepared by averaging the indices of 13 samples for P. smithiana and eight samples for A. pindrow. The maximum lengths of mean ring-width index chronologies are 208 years (1775-1982) for P. smithiana and 371 years (1612-1982) for A. pindrow. Response functions have been developed using the instrumental record of monthly mean temperature and rainfall at Srinagar during the period 1893-1982. Both ring- width chronologies indicate a significant negative response to summer temperature and a significant positive relationship with summer precipitation. Calibration and verification analysis has been carried out for different combinations of months using a multiple species ring-series network and the summer precipitation at Srinagar has been reconstructed back to the eighteenth century. [ABSTRACT FROM PUBLISHER]

This paper examines the rainfall conditions which have prevailed over Africa during the last two decades. Throughout this period rainfall has been abnormally low over most of the continent. These conditions are compared and contrasted with those which previously prevailed during historical and geologic times. A trend towards increasing aridity since about 1970 has been neither continuous nor apparent in all regions but is evident as an increase in the area affected by subnormal rainfall and in the size of the deficit in the semi-arid regions. These conditions contrast markedly with the 1950s and are unlike any which occurred earlier in the century, and may signal a major change in prevailing global- scale climate. The continental patterns of reduced rainfall are analogous to historical fluctuations, most notably those of the early nineteenth century, and are of relevance to understanding the causal mechanisms of climate change in the late Pleistocene. The patterns are supportive of an underlying climatic cause for recent desertification in Africa. [ABSTRACT FROM PUBLISHER]

This paper is the second of a two-part series analysing details of regional, hemispheric and global temperature change during the twentieth century. Based on the grid box data described in Part 1 we present global maps of the strength of regional temperature coherence measured in terms of the correlation decay length for both annual and seasonal mean data. Correlation decay lengths are generally higher for annual rather than seasonal data; higher in the Southern compared to the Northern Hemisphere; and consistently higher over the oceans, particularly the Indian and central north Pacific oceans. Spatial coherence is relatively low in all seasons over the mid to high latitudes of the Northern Hemisphere and especially low in summer over the northern North Atlantic region.We also describe selected regional temperature series and examine the similarities between these and hemispheric mean data, placing emphasis on the nature of the relationships in different seasons. The Equatorial Indian and Atlantic oceans appear to be the best regional proxies for representing global mean temperatures. Temperature change in regions bordering the northern North Atlantic are less representative of hemisphere mean data, particularly in summer.The implications of these results for the large-scale interpretation of high-frequency palaeoclimate proxies are discussed. Strictly, given the length of the instrumental data, our results apply to temperature variability on timescales up to, at most, 50 years. Traditional inferences on global mean temperature change based on regional proxies originating around the margins of the northern North Atlantic must be viewed with some caution. Information on temperature change over the oceans, especially the tropical oceans, is an important prerequisite for accurate portrayal of global mean change. Care must be taken when integrating the evidence of different climate proxies to respect the seasonality of the response. Warm-season temperatures are most atypical of the various seasonal averages, especially in the Northern Hemisphere. Inferring annual temperature change on the basis of summer-responsive data is highly questionable. [ABSTRACT FROM PUBLISHER]

This paper is an up-to-date review of instrumentally-recorded, seasonal, surface temperature change across the land and marine regions of the world during the twentieth century. This is the first part of a two part series. The second part will deal with the interpretation of proxy-climate data in terms of large-scale hemispheric or global-scale temperature averages for the Holocene.In Part 1, we review the uncertainties associated with combining land and marine instrumental records to produce regional-average series. The surface air temperature of the world has warmed 0.5°C since the middle of the nineteenth century. The warming in the Northern Hemisphere only occurred in winter, spring and autumn. Summers are now no warmer than in the 1860s and 1870s. The same half-degree warming is seen in all seasons in the Southern Hemisphere.Spatial patterns of temperature anomalies during two warm decades, the 1930s and 1980s, all vary from season to season. Temperatures during the 1980s were by far the warmest in the last 140 years. Though most areas of the world experienced above normal temperatures, the variability from season to season was notable in the Northern Hemisphere where much of the warmth was in winter and spring over northern and central Asia and northwestern North America. Almost all of the Southern Hemisphere was warmer during these years. [ABSTRACT FROM PUBLISHER]

The Tröllaskagi peninsula is located in northern Iceland, between meridian 19°30'W and 18°10'W, jutting out into the North Atlantic to latitude 66°12'N. The aim of this research is to study recent glacier changes in relation to climatic evolution of the Gljúfurárjökull and Tungnahryggsjökull debris-free valley glaciers in Tröllaskagi. Glacier extent mapping and spatial analysis operations were performed with ArcGIS (ESRI), using analysis of aerial photographs from 1946, 1985, 1994 and 2000, and a 2005 SPOT satellite image. The results show that these glaciers lost a quarter of their surface area between the 'Little Ice Age' and 2005. In this paper, the term 'Little Ice Age' follows Grove (2001) as the most recent period when glaciers extended globally between the medieval period and the early 20th century. The abrupt climatic transition of the early 20th century and the 25-year warm period 1925-1950 triggered the main retreat and volume loss of these glaciers since the end of the 'Little Ice Age'. Meanwhile, cooling during the 1960s, 1970s and 1980s altered the trend, with advances of the glacier snouts. Between the 'Little Ice Age' and the present day, the mean annual air temperature and mean ablation season air temperature increased by 1.9°C and 1.5°C, respectively, leading to a 40-50 m rise in the equilibrium line altitude (ELA) of the glaciers during this period. The response of these glaciers depends not only on the mean ablation season air temperature evolution but also on other factors such as winter precipitation. The models applied show a precipitation increase of up to more than 700 mm since the 'Little Ice Age'. [ABSTRACT FROM AUTHOR]

Proxy data from the northern coast of Ellesmere Island are used to reconstruct Holocene palaeoclimate and appear to corroborate the ice core record from the Canadian and Greenland high arctic despite some regional variation. Geomorphological evidence indicates that deglaciation was associated with a marked climatic amelioration in the late Pleistocene/early Holocene (≥10 ka BP). This contrasts with glaciers on the south side of Grant Land Mountains which started to retreat at 7.5 ka BP perhaps due to significant differences in glacioclimatic regime and the influence of the Arctic Ocean. Indicators of sea ice conditions on northern Ellesmere Island suggest that the early Holocene was a period of considerable open water. Radiocarbon dates on driftwood collected from behind the north coast ice shelves suggest that the ice shelves formed during a mid-Holocene climatic deterioration. Geomorphic evidence shows that the ice shelves are presently breaking up and melting in response to recent warming. Glaciers have responded to Holocene climate change at varying rates which are related to drainage basin size. Many large glaciers are still advancing in response to the mid-Holocene climatic deterioration. Some glaciers display evidence of dual advances which may reflect mid-Holocene and ‘Little Ice Age’ accumulation. Other evidence of ‘Little Ice Age’ cold and recent warmth is perennial snowbank retreat and fluvially eroded ice wedge polygons near sea level. Different cryogenic systems on northern Ellesmere Island have responded to Holocene climate change at various rates: 103 a for glaciers with drainage basin areas >5 km2; 102 a for ice shelves and glaciers <5 km2; and 101 a for sea ice. [ABSTRACT FROM PUBLISHER]

Glaciations in the Cordillera of western North America began during the Late Miocene in the St Elias Range and coastal ranges near Anchorage, Alaska. Radiometric dating of the tephra and lava flows intercalated in the succession of older tills, loesses and outwash deposits permits the reconstruction of the probable early glacial sequence along the Cordillera. No one site shows the complete sequence, but the available data suggest synchroneity of the major glacial events throughout the region.The first evidence for cold conditions at low elevations at midlatitudes is from 3.5 Ma BP. By 2.8 Ma, alpine glaciations may have occurred in the Sierra Nevada and ice wedges had formed in bedrock near Fairbanks, Alaska. Three more major glaciations complete with contemporary periglacial and permafrost landforms had occurred by 1.65 Ma, while at least six more major cold events can be recognized during the Quaternary period. Once again, expansion of permafrost conditions occurred during each event and forms an integral part of the evidence for climatic change. [ABSTRACT FROM PUBLISHER]

A set of paleoflood slack water deposit (SWD) beds was identified within slope clasts at the Jinpingcun (JPC) site in the Jingyuan–Jingtai reaches of the upper Yellow River gorges based on sedimentary criteria and analytical results. Paleoflood hydrology methods were applied to reconstruct paleoflood events in the Jingyuan–Jingtai reaches. The paleoflood peak stages were calculated based on the highest end-point elevations of the SWDs. The HEC-RAS model and optically stimulated luminescence dating enabled robust paleo-discharge estimates to be calculated between 12,750 and 16,310 m3/s for paleoflood events that occurred during 3200–3000 a BP. The peak discharges, including gauged and historical flood data at the Lanzhou gauge station and the reconstructed paleoflood peak discharges at the JPC site, were input for flood frequency analysis. These paleo-hydrological approaches can also be applied to other regions in the Yellow River gorges. Furthermore, the ages of the paleoflood events correspond well with the known climatic events at 3100 a BP during Holocene climatic variability. These findings are significant for flood risk estimation, in the assessment of water sources in dryland environments, and in understanding the interactions between hydrological systems and climatic change in arid and semi-arid regions of the upper Yellow River in China. [ABSTRACT FROM AUTHOR]

Most rich-fen bryophyte species are currently declining and red listed in many European countries. Little is known about their past and current occurrence. We investigated past and recent bryophyte assemblages in mires in the land uplift coast of Finland. The study areas included primary succession areas where mire development started c. 6000 BP. In total, seven mires were studied in two successional transects along the land uplift coast. The past occurrences of rich-fen and other bryophytes were studied in 45 mire stratigraphic peat profiles, and recent occurrences were collected from 158 vegetation plots of 10 m × 10 m. Bryophyte subfossils indicated that the central parts of the basins developed first to wet rich fens with groundwater influence, which developed towards intermediate fens or poorer mire types. Most mire bryophytes occurred in about the same proportion in peat profiles as in recent vegetation. Five rich-fen species (Hamatocaulis lapponicus, H. vernicosus, Meesia longiseta, M. triquetra and Pseudocalliergon trifarium) were clearly more common in peat profiles than in the present mire vegetation, where these species were very rare and appeared only in small patches without sporophytes. These rich-fen species have had markedly wider distributions in the past, probably linked to climate fluctuations, whereas current occurrences are becoming scarce because of multiple anthropogenic factors such mire drainage and climate change. [ABSTRACT FROM AUTHOR]

Coastal marine Holocene deposits of the Apulia region, considered as indicators of palaeoclimatic conditions, were studied. Our data show that (1) up to c. 5500 cal. yr BP, a phase of accumulation of flint pebbles from the Gargano headland occurred at the Riviera sud di Manfredonia (Adriatic coast); their transport from the Gargano headland (north of the study site) is incompatible with the current northward littoral drift and is best explained by a prevalence and dominance of NE and E winds and (2) after c. 4500 cal. yr BP, there was a rapid accumulation of sediments at the Marina di Ugento (Ionian coast), which is best explained by a prevalence and dominance of S, SW and SE winds. The two different wind regimes identified can be explained by a change in the mean pressure configuration in the central Mediterranean. The first phase (until c. 5500 cal. yr BP) consisted of more frequent cyclogenesis to the east-southeast of the Italian Peninsula, followed by a second phase (from c. 4500 cal. yr BP) of more frequent cyclogenesis to the west-northwest. The period between 5500 and 4500 cal. yr BP represents a transitional phase between the two different regimes. In other words, there was a ‘retreat’ of the central Mediterranean cyclogenesis towards the west-northwest. This pattern is contemporaneous with the termination of the African Humid period. We interpret both the ‘retreat’ of the Mediterranean cyclogenesis and the termination of the African Humid period as the expression of an expansion of the tropical dry Saharan belt. [ABSTRACT FROM AUTHOR]

The Northeastern China involves complex interactions between the East Asian summer monsoon (EASM) circulation and the polar climate system, and plays a significant role as the bridge communicating low- and high-latitude climatic processes. High-resolution multi-proxy analysis of a robust accelerator mass spectrometry (AMS) 14C dated lacustrine sediment core recovered from Jingpo Lake in Northeastern China provides a detailed history of EASM variability and vegetation changes since ~5100 cal. yr BP. The period from ~5100 to 3600 cal. yr BP was characterized by the highest pollen percentages of Quercus, Ulmus, Juglans and Corylopsis; low Md (median grain size diameter); and high δ13Corg values, reflecting a relatively warm and humid period. The period between ~3600 and 2100 cal. yr BP is characterized by high Md and low δ13Corg values, and a rapid increase in pollen percentages of herbs, indicating cool and dry climatic conditions. From ~2100 to 150 cal. yr BP, a gradual increase in δ13Corg values and low Md values, and a rapid increase in Carpinus, Juglans and Corylopsis pollen percentages was observed, indicating climate change towards warmer and wetter conditions. After ~150 cal. yr BP, the highest values of total organic carbon mass accumulation rate (TOC-MAR), total nitrogen mass accumulation rate (TN-MAR) and magnetic susceptibility suggesting that the Jingpo Lake region has been severely affected by human activities. The EASM variability in Northeastern China during the mid- to late Holocene shows trends similar to EASM records in China. Furthermore, our findings indicate that the variability of the EASM during the mid- to late Holocene on the multi-decadal to centennial scale was forced by changes in both solar output and oceanic–atmospheric circulation interaction. [ABSTRACT FROM PUBLISHER]

The main goal of this study was to use stable carbon isotopic composition of bulk peat sampled in Tăul Mare-Bardău peat bog, Maramureş Mountains, as a tool to provide paleoclimatic information over the middle and late Holocene in this region. A peat core of 3.60 m was sampled for δ13C analysis, and bulk peat samples were analyzed by isotope ratio mass spectrometry (IRMS) method. δ13C values reveal a maximum variation of 4.69‰ along a 3.6-m-long peat core. We examined the vertical variation of δ13C bulk peat and concluded that several factors could contribute to up core trends of δ13C. Four intervals of climatic variability could be related with variations of δ13C values between ~6800 cal. yr BP and present: two wet periods (around 2800 and 545 cal. yr BP) and two dry periods (6760 and 1430 cal. yr BP). We concluded that variability in the δ13C of bulk peat profile could be influenced most heavily by the water availability, which in turn is related to the amount of precipitation at the time. Four intervals of δ13C variations of the peat sequence between 225 and 25 cm can be related with generally accepted intervals of climatic variability that have occurred within the last 2000–2500 years (‘Roman Warm Period’ (RWP), ‘Dark Age Cold Period’ (DACP), ‘Medieval Warm Period’ (MWP) and ‘Little Ice Age’ (LIA)). The climate was probably of warm–cold alternations, as revealed in our peat core by δ13C variations between 2800 cal. yr BP and present. The δ13C values of the peat profile showed two positive signals at 40 and 225 cm depth and two negative signals at 105 and 350 cm depth. We suggest that these could also represent a change in vegetation at the time. [ABSTRACT FROM AUTHOR]

High-resolution macroscopic charcoal and sediment analysis was used to reconstruct fire history and environmental changes from three loess-paleosol profiles on the semi-arid loess tableland landscape during the Lateglacial period and the Holocene. Analysis of charcoal concentrations, influx, and the ratios of particle-size classes (from which changes in charcoal taphonomy over time are inferred) in the profiles show spatially coherent patterns of change that relate to regional variations in climate. Effective moisture variability on century to millennial timescales and regional differences in fuel availability appear to be the most important controls on fire from the Lateglacial period to the mid Holocene (12,000–3100 yr BP). Conversely, asynchronous fire patterns during the late Holocene appear to indicate regional and temporal variations as well as changing intensities of human activity. Land use intensified in the region during the late Holocene, when the climate became more arid, and a distinct increase in charcoal concentration then indicated an unprecedented increase in biomass burning. The increase in fire activity occurs in the recent loess layer (L0) and the surface soil (TS) consistent with the establishment of irrigated farming for cereal cultivation in the southern part of the study region about 3100 yr BP. Broad-scale land reclamation was extended to the loess tableland region about 2170–1730 yr BP (during the Qin-Han Dynasty period), and the rapidly decreasing charcoal concentration in the accumulated topsoil (at depths of less than 20 cm) at the CCY site since 1500 yr BP is consistent with the development of terrace farming in the northern part of the study region at that time. In summary, the evolution of fire history in the study profiles across the region is closely related to (1) gradients in humidity; (2) spatial and temporal variability in the distribution and intensity of human land use; and (3) the buildup of burnable biomass, among which there was a nonlinear complex relationship during the Holocene. Increased efforts to synthesize and analyze multiple paleo-environmental records and to combine these with multiproxy evidence are needed to understand wildfire history as well as human land use and social cultural development across the region in depth. [ABSTRACT FROM PUBLISHER]

Sedimentary records of the Holocene extraordinary floods were investigated in the upper reaches of the Weihe River, a major tributary in the middle Yellow River basin. Palaeoflood slackwater deposits (SWD) were identified at several sites on the riverbanks. These clayey silt beds are inserted into the Holocene aeolian loess-soil profiles and slope clastic deposits. They have recorded the extraordinary palaeoflood events which occurred between 3200 and 3000 yr BP as dated by OSL method and checked by the archaeological remains of the Neolithic and Bronze Age retrieved from the profile. The minimum flood peak discharges were estimated at between 22 560 and 25 960 m3/s by using palaeohydrological methods. It is 4.5–5.0 times the largest gauged flood (5030 m3/s) that has ever occurred since 1934. The palaeoflood slackwater deposits were found inserted into the pedostratigraphic boundary between the late-Holocene loess (L0) and the mid-Holocene Luvisol (S0) in the riverbank profile. This indicates that the extraordinary flood events were synchronous with the pedogenic regression at the end of the mid-Holocene climatic optimum. The climatic proxies from the studied profile and the correlative profiles in the river valley and the Loess Plateau show that the pedogenic regression was forced by climatic aridity and intensified dust storms and dust falls in connection with monsoonal shift over the Yellow River basin at about 3100 yr BP. The extraordinary flood events were documented not only on the Weihe River, but also on the mainstream and other tributaries of the Yellow River. These suggest that both extraordinary floods and droughts were parts of the climatic variability during the monsoonal shift. These findings are of great importance in understanding the interactions between hydrological system and climatic change in the semi-arid and subhumid regions of the world. [ABSTRACT FROM AUTHOR]

We present fossil pollen data from a sediment core at Lake Grinnell in northern New Jersey of the northeastern United States. The 12 500-yr chronology of the sediment record was controlled by seven calibrated AMS radiocarbon dates on terrestrial plant macrofossils. Similar to many pollen profiles in the region, our data show that vegetation changed from Picea- and Pinus-dominated woodland/forest at 12.5-11.4 ka (1 ka = 1000 cal. yr BP), through Pinus-dominated mixed forest at 11.4-9.3 ka, to Quercus-dominated forest after 9.3 ka. Some main tree taxa, including Tsuga, Ulmus and Acer, arrived and expanded during the Quercus expansion phase at 11.4-9.3 ka in the early Holocene, while other trees, including Fagus and Carya, established and expanded much later around 9 ka. Pollen data show that major forest shifts were in response to climatic change as independently inferred from oxygen-isotope records in the same core. These responses include major turnovers of tree species at the onset of the Holocene after the Younger Dryas, including the disappearance of Picea, declines of boreal taxa Betula and Alnus, and expansions of most other temperate trees. Our new records show two hemlock (Tsuga canadensis) decline events during the Holocene that were both likely caused by climatic change. The early-Holocene hemlock decline centering around 9.5 ka was marked by >10-fold decrease in hemlock populations, which was probably caused by summer high temperature as inferred from high oxygen isotope values. The mid-Holocene hemlock decline from 5.3 ka to 3.0 ka corresponds with a pronounced shift in oxygen isotopes at Grinnell and with a dry climate interval documented from other records in northeastern North America. Our results support the notion that a dry climate caused or triggered the mid-Holocene hemlock decline and that the Appalachian Forest has shown sensitive responses to climatic change in the Holocene. [ABSTRACT FROM AUTHOR]

In September, 2006, we found the remains of timber-sized spruce trees (Picea engelmannii) on the floors of melting ice patches at altitudes of 3465-3480 m in the Mummy Range of north-central Colorado. The ice patches occupy northeast-facing recesses in which windblown snow, scoured from a tundra upland to the southwest, accumulates deeply. We hypothesize that the upland was timbered during the early to middle Holocene. Dense forest vegetation intercepted snow, preventing it from blowing to the recesses, and allowing trees to become established there. Neoglacial cooling led to gradual deforestation of the upland, renewed transport and deposition of snow by wind, and death of the ice-patch trees. Radiocarbon dates show that the trees died between 3860 ± 15 and 3780 ± 20 14C yr BP (c. 4200 cal. yr BP). The trunks show decay similar to that of historic log structures built above timberline during the late nineteenth and early twentieth centuries, suggesting that they have been protected by ice for all but a small portion of the past 4200 years. A series of warm summers and dry winters led to their recent emergence. The study illustrates the importance of monitoring glaciers and ice patches for floral, faunal and archaeological remains whenever severe melting occurs. [ABSTRACT FROM AUTHOR]

The Tagus Prodelta (W Portugal) and the Muros Ría (NW Spain) are areas of high deposition rates registering high-resolution palaeoclimatic records for western Iberia. We compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature (sea surface temperatures and oxygen isotopes), continental input (grain size, iron and magnetic susceptibility) and productivity (inorganic and organic carbon, carbon isotopes, benthic foraminifera and diatoms). Biogeochemical changes in the Tagus Prodelta reflect widely recognized North Atlantic climatic periods encompassing the Roman Period (AD 0-350), the Dark Ages (AD 400-700), the 'Mediaeval Warm Period' (MWP; AD 800-1200) and the 'Little Ice Age' (LIA; AD 1300-1750). The atmospheric North Atlantic Oscillation (NAO) drives the Tagus Prodelta multidecadal, long-term variability in precipitation-river input during cold periods (negative NAO) and marine upwelling during warmer periods (positive NAO), a scheme that is reversed in the Galician region. The Muros Ría shows only local hydrodynamics until AD 1150, including a 'suboxic' event in the inner Ría around AD 500-700. Since AD 1150 Atlantic warm upwelled waters have ventilated the outer Ría but only reach the inner Ría at AD 1750. The twentieth- century records are also interpreted as a reflex of the inverse NAO mode in both areas, resulting in amplification of the LIA biogeochemical water conditions. Centennial-scale solar activity appears to be another important forcing mechanism (or the only one, if solar activity drives the NAO and 'Bond-cycles') behind changes in the hydrography of the Tagus Prodelta, and primary production, bottom ventilation and organic carbon degradation in the Muros Ría. [ABSTRACT FROM AUTHOR]

A core retrieved from Lake Frassino (northern Italy) provided evidence of palaeohydrological change in this area during the last 14 ka. Lithological, malacological and, in particular, stable isotope composition of freshwater shells allowed the delineation of the main phases of lake evolution between the Lateglacial and Holocene. Lateglacial conditions were drier than the Holocene, although a wetter period was inferred before c. 14 ka. According to the oxygen isotope composition of freshwater shells, the Holocene showed a clear bipartition. The first part, which lasted from ∼ 9100 to 7000 yr BP, was drier and was followed by a rapid increase in humidity at ∼ 7000–6800 yr BP. Between ∼ 6800 and 5000 yr BP, there were wetter and more stable conditions, as indicated by smaller δ18O oscillations of Pisidium and Valvata shells. From c. 5000 to 2600 yr BP the record is characterized by larger fluctuations, which may indicate that short-term and particularly pronounced alternation of wet and dry periods occurred. [ABSTRACT FROM AUTHOR]

Dendroclimatology of Cupressus dupreziana, the Tassili cypress, has been attempted on samples obtained from the door beams of the old cities of Ghat and Barkat located at the foot of the Tassili, where the cypress still lives. The tree rings of 20 samples were measured and dated by 24 AMS 14C dates. A mean ring-width chronology has thus been obtained, spanning, though discontinuously, 5220 to 100 14C BP (5990–65 cal. BP). As the tree-ring width in dry lands depends mainly on water availability, the mean ring-width chronology represents a detailed record of changes in rainfall on a decade scale for the middle and late Holocene of the central Sahara. It indicates main drought spells at 5200–5000 14C BP (5900–5760 cal. BP) and at 4350 BP (5120 cal. BP), followed by phases of enhanced precipitation and by the onset of extreme arid conditions at 1550 14C BP (1500 cal. BP). [ABSTRACT FROM AUTHOR]

Vegetation changes during the past 1300 years are reconstructed in western equatorial Africa using a high-resolution pollen record from Lake Kamalété. This small marshy basin (c. 5–7 ha) is located in forest–savanna mosaic in Lopé Reserve (0°43′S, 11°46′E), central Gabon. The Kamalété pollen data show the persistence over the past 1300 years of a relatively stable forest–savanna mosaic, associated with significant changes of the forest component. Three successive stages of forest dynamics occurred. First, at 1325 cal. BP, moist semi-evergreen rainforest existed around the catchment of Lake Kamalété. However, it appears from the consistent presence of >70% Gramineae pollen that the site was always primarily in savanna. Secondly, from c. 1240 to 550 cal BP, a noticeable increase in shade-intolerant plant species indicate openings in the rainforest canopy. The persistence of gap-colonizer species, such as Macaranga, Tetrorchidium and Musanga for several centuries in the rainforest, is explained by recurring canopy disturbance associated with shifts in available moisture. These hydrological changes may be related to a succession of longer and more severe dry seasons than observed today. Thirdly, at 550 cal BP, mature forest was re-established, corresponding to progressive savanna colonization by forest pioneer species such as Aucoumea klaineana, Lophira alata and Fagara macrophylla. This new phase of forest expansion coincided with a marked lithological change, indicating an increase in lake-level. It is concluded that the major vegetation changes observed are due to climatic variability, and anthropogenic action had limited influence. [ABSTRACT FROM AUTHOR]

A 267-cm sediment core spanning the past c. 15200 cal. yr was recovered from Mumbo Lake, in the Trinity Mountains of northwestern California's Klamath Region. Plant macrofossils and pollen detail local and extra-local vegetation history, while high-resolution charcoal analysis provides details on local fire history. For the first c. 3000 years, climate was colder and drier than present, and supported an open, subalpine parkland vegetation, with low fire frequencies and fuel biomass. From c. 12100 to 9800 cal. yr BP increasing moisture and soil development led to a woodland community with three new pine species invading the basin. Fire frequencies remained low, but individual fires may have been more intense because of increased fuel loads. Between c. 9800 and 7200 cal. yr BP, climate warmed and dried considerably, allowing for the expansion of oak and other chaparral species. Fire frequencies increased in the early Holocene, but low charcoal accumulation rates suggest a frequent, relatively low-intensity fire regime. From c. 7200 to 3800 cal. yr BP, the climate became cooler and moister again. Many conifer species appeared for the first time, although chaparral species maintained a strong presence. The fire record shows a dramatic increase in charcoal accumulation rates as well as an increase in fire frequency. From c. 3800 cal. yr BP to present, more conifer species enter the record, and abundance of chaparral species gradually diminishes to present levels. [ABSTRACT FROM AUTHOR]

At 3.5 Ma, the Arctic Ocean was unfrozen, and only during the second Pliocene cold event (Californian – 3.0 Ma) did an extensive glaciation occur in Alaska-Yukon and Iceland. The sea froze during the third (Alaskan – 2.58 Ma) event as the western Arctic cooled rapidly. Baffin Island and Labrador were the centres of ice sheets, and ice-rafted debris appeared in the North Atlantic. Shrub-tundra replaced boreal forest in the west during the next warm episode but forested-shrub-tundra persisted in north Greenland during the next (Wyoming – 2.2 Ma) cold event. During the last Pliocene (Montanan – 1.9 Ma) cold event, tundra surrounded the Arctic basin with widespread permafrost in unglaciated areas. Quaternary cold events were more frequent, with tundra persisting on land during warm episodes, although coastal seas usually thawed seasonally. There was a continuous cooling trend due to the demise of the Tethyan sea, but the 18O marine curve shows about 130 fluctuations compared with 14 major cold events on land. The cause of the terrestrial changes seems to be the interaction of many cyclical controls with different periodicities. When enough cycles are synchronized for air temperature to cross a critical threshold, a climatic change occurs. The critical thresholds are dependent on local environments and latitude. [ABSTRACT FROM AUTHOR]

We present a method of multiproxy reconstruction of the climate of Europe during the last millennium. The proxies used comprise long tree-ring width series, grape harvest dates, Greenland ice oxygen isotope series and temperature indices based on historical documents. The proxies are calibrated using gridded April to September mean temperatures for western Europe, i.e., between 10°W and 20°E and between 35°N and 55°N. They are calibrated also using the long instrumental summer temperature series of the Marseilles observatory of Longchamp, which begins in the mid-eighteenth century. The method is a combination of an analogue technique, which is able to deal with missing data, an artificial neural network technique for an optimal non-linear calibration and a bootstrap technique for calculating error bars on the reconstruction. About 70% of the temperature variance is reconstructed. The amplitude of the past temperature variations is particularly well reconstructed, which is important when considering whether the recent temperature trend is or is not within the natural variability. It appears that the temperature of the last decade of the twentieth century was reached only 14 times during the last millennium. The reconstruction is discussed with respect to other multiproxy and borehole temperature reconstructions. We conclude that a reconstruction such ours, with a specific regional focus (as opposed to the larger Northern Hemisphere) is more reliable and is in better agreement with borehole results, even allowing for the fact that only a part of the long-term variance is reconstructed. 'Little Ice Age' (c. AD 1560 – 1930) summers were 0.2±0.5°C cooler than the 1961 – 1990 period. Borehole temperatures indicate a cooling of 0.4°C which falls in the 95% confidence interval of our reconstructions. [ABSTRACT FROM AUTHOR]

Records of geomagnetic secular variation have been obtained from three cores recovered from the Salerno Gulf (southern Italy). High-resolution petrophysical and palaeomagnetic measurements enabled the reconstruction of a composite curve of geomagnetic palaeosecular variation (PSV), which is compared with the reconstructed PSV curve from Britain and with the French archaeomagnetic data of the last 2.1ka. The good agreement of the Salerno Gulf record with the above data confirms that our PSV record reaches back for some 9.0ka. In addition to a thick pumice layer originated during the Somma-Vesuvius eruption at AD 79, two other tephra layers were recognized, at about 1.3 and 3.0ka BP, that are probably also of Vesuvian origin. The comparison provides an initial chronological framework for assessing the increasing trend of sedimentation rate and its significant changes at about 2.7ka and 7.0ka BP. This variation in the deposition rate suggests a link with climatic changes recognized in the Mediterranean region. [ABSTRACT FROM AUTHOR]

To investigate postglacial environmental changes in both the coastal and interior wet belts of British Columbia, fossil midges were analysed from two subalpine lakes, one adjacent to the lower Fraser canyon (Frozen Lake), and the other in Mount Revelstoke National Park (Eagle Lake). The midge stratigraphy for Frozen Lake revealed an abundance of rheophilous chironomid taxa and Simuliidae larvae, reflecting the presence of an inflowing stream. An abundance of Chaoborus mandibles and Microtendipes during the early Holocene (c. 10100-7700 [sup 14]C years BP, c. 11500-8500 cal. years BP) suggests warmer temperatures. A subsequent decline in the warm indicators and relative increases in cold stenotherms (Heterotrissocladius and Diamesa) indicate cooling until present day. This climate reconstruction is consistent with other quantitative and qualitative evidence for past climatic change in southern British Columbia. At Eagle Lake the warm indicators, Dicrotendipes and Polypedilum, are seen in the early Holocene (c. 8500-6730 [sup 14]C years BP, c. 9600-7600 cal. years BP), but are absent during the mid-Holocene when cooler temperatures probably prevailed. In the late Holocene (c. 3800 [sup 14]C years BP to present, c. 4200 cal. years BP to present) there is a resurgence of warm indicators, which contrasts with the evidence of continued cooling typically seen in reconstructions of southern British Columbia summer temperatures. The Eagle Lake record therefore appears to be anomalous. Multiproxy and multisite investigations are needed to reconstruct Holocene climatic changes more reliably. [ABSTRACT FROM AUTHOR]

Biostratigraphic diatom analyses were carried out on two sediment cores from Igaliku Fjord, South Greenland, in order to reconstruct hydrographic and climatic fluctuations during the late Holocene (AD 550 to present). Pronounced differences in hydrographic setting of the coring sites provide palaeoenvironmental information of both local and more regional character. Five diatom zones were identified from the subfossil diatom records, each describing a hydrographic setting. Two major climate periods, the 'Mediaeval Warm Period' (AD 800–1250) and the 'Little Ice Age' (AD 1580–1850), that were separated by a variable transitional period, were recognized. Prior to these periods, a cold and presumably moist climate regime prevailed between AD 500 and 700. Cooling events were identified during the 'Mediaeval Warm Period' in the period AD 960 to 1140. The diatom data demonstrate that marked hydrographic changes occurred in the course of a relatively short timespan beginning at about AD 1300 and culminating around AD 1500. These changes occur during a crucial period in which the Norse are believed to have disappeared from South Greenland. Thus, our results support the hypothesis proposing that one of the main reasons for the loss of the Norse settlements was climatic deterioration. [ABSTRACT FROM AUTHOR]

A high-resolution record of late-Holocene subsurface water-mass characteristics in outer Igaliku Fjord, South Greenland, is presented based on benthic foraminifera faunas from core PO 243-451 collected from a water depth of 304 m. Stratification with Atlantic water masses present in the lower part of the watercolumn is suggested to have prevailed during the last 3200 cal. years, except for a period referred to as the 'Mediaeval Warm Period' (MWP). During the MWP (c . AD 885-1235) the outer part of Igaliku Fjord experienced enhanced vertical mixing and a high hydrodynamic energy level which we ascribe to increasing wind stress through this period, corresponding to the period of the Norse settlement. The transition from the MWP to the 'Little Ice Age' (LIA) shows a two-step pattern with a short climatic amelioration around AD 1520 before maximum cooling occurred. The intensified wind stress and the overall environmental change are suggested to have contributed to the loss of the Norse settlement in Greenland. Periods with strong stratification and marked influence of Atlantic subsurface water masses around 2.6, 1.3 ka BP and during the LIA are correlated to North Atlantic Holocene ice-rafting events reported by Bond et al. (1997). [ABSTRACT FROM AUTHOR]

The stable isotope records of four stalagmites dated by 19 TIMS uranium series ages are combined to produce master chronologies for δ[sup 18]O and δ[sup 13]C. The δ[sup 18]O records display good overall coherence, but considerable variation in detail. Variability in the δ[sup 13]C records is greater, but general trends can still be discerned. This implies that too fine an interpretation of the structure of individual isotopic records can be unreliable. Speleothem δ[sup 18]O values are demonstrated to show a positive relationship with temperature by comparing trends with other proxy records, but also to respond negatively to rainfall amount. Speleothem δ[sup 13]C is considered to be most influenced by rainfall. The postglacial thermal optimum occurred around 10.8 ka BP, which is similar in timing to Antarctica but up to 2000 years earlier than most Northern Hemisphere sites. Increasingly negative δ[sup 18]O values after 7.5 ka BP indicate that temperatures declined to a late mid-Holocene minimum centred around 3 ka BP, but more positive values followed to mark a warm peak about 750 years ago which coincided with the 'Mediaeval Warm Period' of Europe. Low δ[sup 18]O values at 325 years BP suggest cooling coincident with the 'Little Ice Age'. A marked feature of the δ[sup 13]C record is an asymmetric periodicity averaging c. 2250 years and amplitude of c. 1.9‰. It is concluded that this is mainly driven by waterbalance variations with negative swings representing particularly wet intervals. The δ[sup 18]O record shows a higher-frequency cyclicity with a period of c. 500 years and an amplitude of c. 0.25 ‰. This is most likely to be temperature-driven, but some swings may have been amplified by precipitation. [ABSTRACT FROM AUTHOR]

This study characterizes late-Holocene (past 3300 years) variations in organic matter deposition in the outer part of Igaliku Fjord, South Greenland, and uses this information to assess palaeohydrographic conditions. Except for two, all residues were characterized by abundant organic matter, with amorphous material dominating. The late-Holocene sediments in the deeper parts of the outer Igaliku Fjord have generally been deposited under anoxic to suboxic conditions with relatively low terrestrial/freshwater influx. The organicwalled dinoflagellate cyst assemblages suggest the continuous presence of water masses derived from the East Greenland Current, while changes in sea-surface temperature during the last 3300 years have also been interpreted. Terrestrial influx was reflected by the continuous occurrence of leaf tissue, which increased in abundance in sediments younger than AD 960. Pseudo-amorphous phytoclasts occurred in sediments older than AD 770, and sporomorphs were rare throughout. Acritarchs and organic-walled dinoflagellate cysts dominated the assemblages in the sediments. Relatively high amounts of benthic foraminiferal linings in the interval AD 960-1285 suggests increased nutrient availability, which may be ascribed to strong, wind-induced mixing of the watercolumn or higher fluxes of organic material. Sparse organic matter was recorded in sediments of age c. AD 1125 pointing to significant oxidation due to highly oxic bottom-water conditions. [ABSTRACT FROM AUTHOR]

The ideas behind peatland restoration and the utility of testate amoebae in informing such schemes are briefly reviewed and discussed in the context of two lowland raised-mire sites in northwest England (Astley Moss, part of the Chat Moss complex in Greater Manchester, and Danes Moss, Cheshire). Our study indicates a high degree of correspondence between the sites in their response to major documented climatic deteriorations during the last five millennia. In particular, the c. 2300 BP event appears to correspond with greatly increased water-table fluctuation at both sites and pronounced declines in characteristic mire taxa of testate amoebae. These do not regain their former dominance save for a brief episode at c. 300 BP affecting both sites. Despite some restoration attempts at both sites, testate assemblages bear little resemblance to what might he considered a typical mire assemblage and do not appear to have done so with any degree of stability for c. 2500 years. This raises important issues regarding the practicability and suitability of such sites for large-scale restoration attempts and the range of conditions that can he considered natural for such sites: these questions should form the basis of future research. [ABSTRACT FROM AUTHOR]

Results of a fossil Coleoptera (beetle) fauna from a fen edge sequence from Hatfield Moors, Humber-head Levels, England, are presented, Mire ontogeny inferred from this location and others are discussed, particularly in the light of previous palynological and plant macrofossil investigations. Peat initiation across most of the site centres around 3000 cal. BC, characterized by a Calluma-Eriophorum heath with areas of Pinus-Betula woodland. The onset of peat accumulation on the southern margins of the site was delayed until 1520 1390 cal. BC and appears to overlap closely with a recurrence surface at a pollen site (HAT 2) dated to 1610 1440 cal. BC, suggesting that increased surface wetness may have caused mire expansion at this time. The faunas illustrate the transition from eutrophic and mesotrophic fen to ombrotrophic raised mire, although the significance of both Pinus- and Calluna-indicating species through the sequence suggests that heath habitats may have continued to be important. Elsewhere, this earlier phase of rich fen is lacking and mesotrophic mire developed immediately above nutrient-poor sands, with ombrotrophic conditions indicated soon after. Correspondence analysis of the faunas provides valuable insights into the importance of sandy heath habitats on Hatfield Moors. The continuing influence of the underlying coversands suggests these may have been instrumental in mire ontogeny. The research highlights the usefulness of using Coleoptera to assess mire ontogeny, fluctuations in site hydrology and vegetation cover, particularly when used in conjunction with other peatland proxies. The significance of a suite of extinct beetle species is discussed with reference to forest history and climatic change. [ABSTRACT FROM AUTHOR]

We examined the variations in vegetation, organic carbon isotopic compositions and biomarker distributions spanning a well-constrained climatic shift in a Sub-Boreal Dutch raised bog. The macrofossils record a vegetation shift from a predominance of degraded Ericaceae rootlets to a predominance of well-preserved Sphagnum species, first S. cuspidatum, followed by S. imbricatum. This shift, as well as evidence from other macrofossils and fungal spores, indicates that the local climatic conditions changed from relatively dry to relatively wet, with the wettest local conditions occurring at the base of the transition. At this boundary, a positive shift occurs in the δ[sup 13]C values of bulk peat (c. 4‰) and compounds derived from specific peat-forming plants (1 to 2‰). This is attributed to a combination of factors, including selective preservation of certain compound classes, changes in precipitation and its effect on the water table, and plant growth rates. The changes in peat preservation also indicate that redox changes occurred across the climatic change event. Indeed, biomarker transformations thought to reflect past redox conditions or bog water acidity - the 1,2,9-trimethyl1,2,3,4-tetrahydropicene to ursolic acid ratio, diacid to hydroxy acid ratio, and 17β,21β(H)-homohopane to total homohopane ratio - all exhibited shifts spanning the climatic change transition. Although some of these trends indicate the need for more fundamental research on biomarker transformations in peat, some, such as the 17β,21β(H)-homohopane to total homohopane ratio, show promise as indicators of past bog water conditions that could complement macrofossil analyses. [ABSTRACT FROM AUTHOR]

We reconstructed the late-Holocene surface-moisture history and vegetation dynamics of a raised bog in Michigan using testate amoebae, peat humification, pollen, stomata and plant macrofossils. Our primary objective was to compare bog palaeohydrology with the water-level history of Lake Michigan, and to regional and local vegetation changes. Hydrologic histories inferred from testate amoebae and humification show similar trends, and correspond with records of past water-level variability in Lake Michigan. The bog clearly shows effective-moisture increases during the Algoma highstand (~3200-2300 cal. BP) and a later unnamed highstand (~1900-1300 cal. BP). Some higher-frequency fluctuations are also similar. The good correspondence indicates that bog hydrology and the water levels of Lake Michigan have been driven by changes in large-scale atmospheric circulation patterns for at least the past 3500 years. Climate during the Algoma highstand may have been spatiotemporally complex, with increasing moisture occurring several hundred years earlier in the northern portion of the western Great Lakes basin. Locally, the expansion and contraction of Picea populations on the bog surface was probably directly related to moisture conditions. The well-documented decline in Fagus populations in the central Great Lakes region after 1000 cal. BP is contemporaneous with a major shift towards drier conditions, suggesting that relative dryness caused the decline. [ABSTRACT FROM AUTHOR]

Conspicuous grey, clay-rich flood deposits in the predominantly olive, varved sediment in the central Santa Barbara Basin, California, were dated via varve-counting to c. AD 212, 440, 603, 1029, 1418 and 1605. The ~200-yr quasi-periodicity and the timing of individual floods match time periods of known supraregional climatic changes and the documented ~200-yr periodicity in palaeoclimate records elsewhere. The floods of c. AD 440 and AD 1418 occurred during global reorganizations of atmospheric circulation. Cold spells seem to have accompanied the floods of c. AD 1029 and AD 1605. California floods and other palaeoclimate records suggest that expressions of regional climates are modulated by solar variability with a ~200-yr periodicity. Our compilation of palaeoclimatic and Mesoamerican and South American archaeological records provides evidence that palaeoenvironmental and cultural changes were often coincident within their respective dating uncertainties and occurred in ~200-yr steps. The matching pattern supports the hypothesis that manifestations of changing climates, such as drought or flooding, served as destabilizing cofactors in transitions of precolumbian cultures. Extrapolation of the ~200-yr recurrence pattern of Santa Barbara flooding suggests that catastrophic flooding in southern California may be expected for the early part of this century. [ABSTRACT FROM AUTHOR]

Annually laminated sediments from Lake Van, spanning about 13000 varve years, were sampled for stable-isotopic, geochemical, pollen and charcoal analyses in order to find evidence of past regional climatic changes and human impact in the semi-arid region of eastern Anatolia, Turkey. The Lateglacial period was cold and dry, with steppe vegetation and saline lake water. During the Younger Dryas the lake level dropped dramatically, and the vegetation turned to a semi-desert. Geochemical and isotopic records indicate a strong increase in moisture at the onset of the Holocene, and Artemisia-chenopod steppes were partly replaced by grass steppe and pistachio scrub. A delay of about 3000 years in the expansion of deciduous oak woodlands and high steppe-fire frequencies suggest dry spring and summer weather during the early Holocene. At 8200 yr BP, a shift in the regional climate regime facilitated the transport of more moisture into the interior areas of the Taurus mountains and caused a change in the seasonal distribution of precipitation. The steppe-forests dominated by Quercus advanced and reached their maximum extention at about 6200 yr BP. All the proxy data indicate optimum climatic conditions, low water salinity and high lake level between 6200 and 4000 yr BP. After 4000 yr BP, aridity increased again and the modern climatic situation was established. Human impact in the catchment of Lake Van started at 3800 yr BP and was intensified during the last 600 years. [ABSTRACT FROM AUTHOR]

We have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century-scale abrupt changes in Asian monsoon precipitation since the last deglaciation. We identify abrupt events from (1) the interpretations of the authors of these records and (2) the more objective moving t-test calculation. Our results indicate that abrupt climatic changes occurred at ~11.5 cal. ka, ~4.5–5.0 cal. ka and AD 1300. At the start of the Holocene (~11.5 cal. ka), Asian monsoon precipitation increased dramatically. This climatic change is synchronous with an abrupt warming in the North Atlantic. During the middle Holocene, there was a time of preferred and widespread weakening in monsoon strength (~4.5–5.0 cal. ka). This result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time. The middle-Holocene abrupt event could have been synchronous with an abrupt cooling event in the North Atlantic, as well as a warming and intensification of internannual variability in the tropical Pacific. In contrast to previous periods, precipitation changes at AD 1300 have a heterogeneous spatial pattern. We find no conclusive evidence for a change in the Asian monsoon at ~8.2 cal. ka, as suggested by several previous studies. More high-resolution data may be needed to observe this short-lived event. Overall, our results attest to the potential for rapid and major shifts in Asian monsoon precipitation that may be triggered by variations in other components of the climatic system. [ABSTRACT FROM AUTHOR]

The understanding of natural and anthropogenic climatic change is an important issue in recent studies. The influence of the Sun (11-year solar cycle) as a natural variability factor on the atmosphere is discussed. Statistical studies with observational data (NCEP/NCAR re-analyses) covering four solar cycles show high correlations between the 11-year solar signal and meteorological parameters, e.g., the geopotential heights and temperatures, in the lower stratosphere and troposphere. Studies with general circulation models (GCM) have discussed the possibility of an indirect dynamical response to direct changes in solar irradiance and ozone in the stratosphere. A physical mechanism explaining the solar influence on the atmosphere is still missing. Part of the mechanism understood so far and ideas from model and observational studies are presented. [ABSTRACT FROM AUTHOR]