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New stratigraphic evidence for the Holocene history of three glaciers in central Jotunheimen, southern Norway, is presented and the implications for century- to millennial-scale glacier and climatic variability are considered. Minerogenic layers in seven stream-bank mires, flooded episodically by glaciofluvial meltwater, are dated by 79 new radiocarbon age estimates. A revised chronology for glacier variations in Smørstabbtindan suggests a three-phase Holocene: (1) an early-Holocene deglaciation phase (11 500-9500 cal. BP) characterized by readvances of ice-sheet remnants; (2) a mid-Holocene phase with relatively small or absent glaciers (9500-5000 cal. BP); and (3) a late-Holocene phase of enlarged and fluctuating glaciers (the last 5000 years). Seven millennial-scale neoglacial events (Smørstabbtindan I-VII), during which glaciers were larger than at present for most of the time, are dated to: >10 400-9600 (Erdalen Event), 8400-7650 (Finse Event), 4800-3900, 3200-2550, 2350-1700, 1400-750 and 500-0 cal. BP ('Little Ice Age'). Two or more century-scale events are nested within each millennial-scale event. Based on the timing of neoglacial maxima, the record from Smørstabbtindan is combined with comparable reconstructions from southern Norway to indicate at least 17 century- to millennial-scale Southern Norwegian Neoglacial Events. A similar approach to records from the Swiss and Austrian Alps identifies around 23 Alpine Neoglacial Events. This leads to the recognition of 13 European Neoglacial Events that are at least continental in extent but seem to be imperfectly correlated with episodes of low solar irradiance, which suggests that other climatic forcing factors are also involved, including volcanic aerosols and, in the early Holocene, freshwater outbursts into the northern Atlantic Ocean. Local to regional patterns in glacier behaviour, particularly in relation to century-scale events, may be accounted for by differences in glacier size and geometry, topography and atmospheric circulation patterns; whereas the three Holocene multimillennial phases appear to reflect the Earth's orbital variations. [ABSTRACT FROM AUTHOR]

The modern floristic composition of the principal raised bogs of Wales is significantly altered compared with their histories of development from the early to mid Holocene. This paper uses pollen and plant macrofossil records from two raised bogs together with previously published data from a further two sites to explore the key factors contributing to the present condition of Welsh ombrotrophic plant communities. Results show Betula and Molinia invasion is a recent feature of bog development in Wales. Previous Holocene ‘dry-phases’ were characterized by Ericaceae and Pinus establishment, supporting recent experimental evidence that Betula and Molinia encroachment is primarily a response to nitrogen (N) loading rather than desiccation on intact bogs. Several of the bogs featured in this study also show severe signs of structural damage, not only from peat cutting but, in the case of Cors Caron, from channel processes in the adjacent River Teifi. Radiocarbon dating and inter-site comparisons of peat accumulation rates show that Rhos Goch Common in particular has been heavily impacted by peripheral peat cutting, leading to dewatering, significant subsidence of its peat dome and the spread of hummock and high dry ridge communities. Finally, the decline and local extinction of Sphagnum austinii in bogs across Europe represents one of the most significant changes in ombrotrophic community composition in the late Holocene. Co-registered pollen and macrofossil evidence from Cors Caron demonstrates that increases in landuse intensity over the last 2000 years are temporally associated with reductions in the abundance of S. austinii and ultimately its local disappearance from the palaeoecological record. [ABSTRACT FROM AUTHOR]

Management of peatlands for conservation purposes is often directed at mitigation of damaging impacts of past and present human activity. Assessment of such impacts is often based on perspectives from short-term ecological data. Here we test a series of hypotheses for the causes of changes in mire hydrology and vegetation on the Border Mires in northern England using palaeoecological data for the last 200 years. Ecological data suggest peatlands surrounded by plantation forestry have become drier over the last 40 years. This could be caused by direct hydrological impacts of the growing trees and associated drainage or indirectly by the cessation of grazing and burning. A third hypothesis is that hydrological changes are the result of recent climatic change. High-resolution water-table reconstructions from testate amoebae analysis supported by plant macrofossil analysis and dated by [SUP210]Pb, spheroidal carbonaceous particles (SCPs) and pollen data demonstrate that a site outside the direct influence of forestry has also become drier during the twentieth century. This suggests that forestry is not the main cause of changes observed on other sites. Water-table declines began earlier than the main phase of forest planting and the magnitude of change appears to be similar to that on a site within the forest. Subjective comparisons of reconstructed water tables with meteorological data suggest that hydrological changes on the mires are primarily driven by summer temperature changes. If future regional climatic change predictions are correct, further water-table decline will follow and current management activities are unlikely to restore mires to their former condition. [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]

Equations based on empirical relationships of peat physical properties were used to estimate the average long-term apparent rate of carbon accumulation (LORCA) in Finnish mire vegetation regions. The results were generalized to the boreal and subarctic regions. Analyses of 1302 dated peat cores were used to infer carbon accumulation for each mire vegetation region of Finland. The area-weighted LORCA for Finnish undrained mire areas was 18.5 g m[sup -2] yr[sup -1] and the total carbon sink 0.79 Tg yr[sup -1] (1 Tg = 10[sup 12]g). The total carbon pool of Finnish undrained mires was estimated as 2257 Tg. The aapa-mire region included 80% of the total net accumulation rate of carbon and 85% of the total carbon reservoirs of Finnish undrained mires. LORCA was significantly higher in the raised-bog region, 26.1 g m[sup -2] yr[sup -1], compared with the aapa-mire region, 17.3 g m[sup -2] yr[sup -1], and bogs generally had a higher LORCA 20.8 g m[sup -2] yr[sup -1], than fens 16.9 g m[sup -2] yr[sup -1]. The total C sink for boreal and subarctic mires was estimated at 66 Tg yr[sup -1] which is about 31% lower than the previous estimates. The total C pool of all boreal and subarctic mires was estimated at 270-370 Pg (1 Pg = 10[sup 15]g). [ABSTRACT FROM AUTHOR]

The fire history and the effect of fires on the long-term (apparent) rate of carbon accumulation (LORCA) in the Patvinsuo mire complex, eastern Finland, were determined through stratigraphic and pollen analyses of 98 peat cores. The peat cores were characterized by a large number of charcoal layers and the age of the basal peat varied between 57 and 10 500 years. Mire fires slowed down the progress of vertical peat accumulation and resulted in great carbon losses. The average LORCA in the Patvinsuo cores was clearly lower, 9.2 ± 1.0 (SE) g m -2 yr -1 , compared to the average value for all mire sites in the southern half of Finland, 17.7 ± 0.6 (SE) g m -2 yr -1 . The average rate of carbon loss in Patvinsuo mire complex was 9.5 ± 1.0 (SE) g m -2 yr -1 and the mean carbon loss in an individual fire was estimated to be 2.5 kg m -2 . [ABSTRACT FROM AUTHOR]

Raised bogs represent end-products of peatland development that are generally assumed to be decoupled from the regional groundwater system. However, the development of two peat mounds in northern Minnesota was driven by three major reversals in its groundwater-flow regime. A 4000-year record of groundwater flow was reconstructed by stratigraphic studies that utilized both botanical indicators of the surface-water chemistry, and mineral indicators of the pore-water chemistry and chemical weathering regime. The mineral stratigraphy indicated that the peat mounds were initially formed under a discharge (upward flow) regime. During the succeeding moist period, these peat mounds developed into raised bogs as their water-table mounds drove local recharge (downward) flow into the mineral substratum. A major reversal to a prevailing discharge regime at 1200 BP, however, converted the smaller peat mound into a spring fen and weathered the silicate minerals within the peat profile of the larger mound. This reversal was apparently caused by the onset of extended droughts, which dissipate the water table mound within these peat landforms. [ABSTRACT FROM PUBLISHER]