A 7500-year peat-based palaeoclimatic reconstruction and evidence for an 1100-year cyclicity in bog surface wetness from Temple Hill Moss,Pentland Hills,southeast Scotland

Analyses of plant macrofossils, peat humification and testate amoebae were used to reconstruct a proxy climate record spanning the last 7500 years from an ombrotrophic bog, Temple Hill Moss, in southeast Scotland. The plant macrofossil data were subjected to detrended correspondence analysis (DCA) which modelled effectively the significant wet shifts within the record. A mean water table depth transfer function was applied to the testate amoebae data to provide quantifiable changes. The three proxy records show coherent phase changes which are interpreted as variability in past effective precipitation. Two tephra horizons (Glen Garry and Lairg A) were used in conjunction with radiocarbon dates to construct an age/depth model, producing a robust geochronology from which a time series was calculated. The palaeoclimatic reconstruction identified major wet shifts throughout the Holocene, with specific events occurring around cal. 6650, 5850, 5300, 4500, 3850, 3400, 2800–2450, 1450–1350 and 250–150 BP. Spectral analysis of the plant macrofossil DCA and colorimetric humification data produced a millennial scale periodicity of 1100 years. The same periodicity has also been found in a palaeoclimatic reconstruction from a site in Cumbria (Walton Moss), and may be linked with millennial scale periodicities found in oceanic palaeoclimatic records.     

A proxy record of late Holocene climate change from May Moss,northeast England

Quantitative reconstruction of changes in mire surface wetness has been used to reconstruct proxy climate from an upland ombrotrophic blanket mire on the North York Moors in northeast England (May Moss). Testate amoebae, plant macrofossil and humification analyses were carried out for six peat profiles. Transfer functions are used to generate estimates of water table levels from the testate amoebae stratigraphy, which complement the semi‐quantitative indications of changing surface wetness provided by plant macrofossil and humification analysis. ¹⁴C dates provide the chronology for the stratigraphy. Differences were encountered between AMS ¹⁴C dates on pure Sphagnum remains and radiometric dates on bulk peat from the same horizon, which perhaps arise from the heterogeneity of peat. Replicate palaeoecological analysis of adjacent cores identifies consistency within testate amoebae and plant macrofossil stratigraphies, and reveals a strong agreement between the water table level proxies. The record of hydrological changes at sites across May Moss are in synchrony, and so climate change is the most likely cause of the moisture fluctuations. Changes to a wetter or cooler climate were identified cal. ad 260–540, ca. ad 550–650, cal. ad 670–980, ca. ad 1350–1450, cal. ad 1400–1620 and ca. ad 1700–1800. Periods with a drier or warmer climate precede all of these wet shifts, with particularly dry periods between cal. ad 650–860 and 690–980 and between cal. ad 1290–1410 and 1400–1620. Copyright © 2001 John Wiley & Sons, Ltd.     

Can rapidly accumulating Holocene peat profiles provide sub‐decadal resolution proxy climate data?

To test the potential for developing sub‐decadal resolution records of ombrotrophic bog surface wetness (BSW), selected abrupt climate events were identified in cores from four sites in north‐west Europe and time‐slices over each event were investigated at 2–5‐mm resolution using peat humification, testate amoeba and plant macrofossil analyses. Age–depth models based on radiocarbon, spheroidal carbonaceous particle and tephra dates were applied and the error in these models was used to determine the effective temporal sampling resolution, which in most cases was sub‐decadal. Fine‐resolution results revealed some inconsistencies in the co‐variability of individual proxies and there was a lack of correspondence between some results from adjacent cores. However, we found evidence of abrupt shifts in BSW occurring over ca. 5–20 years, indicating a more rapid proxy response than identified in previous research. To maximize potential temporal resolution and produce reliable sub‐decadal BSW data in future research, we recommended that peat‐based studies should obtain the best possible chronological control, focus on sites with high species diversity and rapid accumulation rates and perform replicate coring, or use open peat sections where the stratigraphy can be clearly seen, to assess intra‐site differences in microtopography. Site‐specific factors should be a primary consideration in the selection of sites for future fine‐resolution research. Copyright © 2012 John Wiley & Sons, Ltd.     

The climate of Scotland over the last 5000 years inferred from multiproxy peatland records: inter‐site correlations and regional variability

The mid to late‐Holocene climates of most of Scotland have been reconstructed from seven peat bogs located across north–south and east–west geographical and climatological gradients. The main techniques used for palaeoclimatic reconstruction were plant macrofossil, colorimetric humification, and testate amoebae analyses, which were supported by a radiocarbon‐based chronology, aided by markers such as tephra isochrons and recent rises in pine pollen and in spheroidal carbonaceous particles (SCPs). Field stratigraphy was undertaken at each site in order to show that the changes detected within the peat profiles were replicable. Proxy climate records were reconstructed using detrended correspondence analysis (DCA) of the plant macrofossil data and a mean water table depth transfer function on the testate amoebae data. These reconstructions, coupled with the humification data, were standardised for each site and used to produce a composite record of bog surface wetness (BSW) from each site. The results show coherent wet and dry phases over the last 5000 years and suggest regional differences in climate across Scotland, specifically between northern and southern Scotland. Distinct climatic cycles are identified, all of which record a millennial‐scale periodicity which can be correlated with previously identified marine and ice core Holocene cycles. The key role of the macrofossil remains of Sphagnum imbricatum, a taxon now extinct on many sites, is discussed in relation to the identified climatic shifts. Copyright © 2005 John Wiley & Sons, Ltd.     

Response of testate amoeba assemblages to environmental and climatic changes during the Lateglacial–Holocene transition at Lake Lautrey (Jura Mountains,eastern France)

We tested the response of lacustrine testate amoebae (thecamoebians) to climate and environmental changes for the Lateglacial–Holocene transition. The palaeoenvironmental history of the study site (Lake Lautrey, Jura Mountains, eastern France) was previously established based on high‐resolution multi‐proxy studies of the same core. The present study is characterised by a high taxonomic resolution (54 taxa), inclusion of small species (down to 25 µm) and high total counts (>500 individuals per sample on average). Changes in the composition of testate amoeba assemblages (dominant species and assemblage structure), as well as in the accumulation rate (tests cm^?2 a^?1), corresponded to major climatic phases (i.e. Oldest Dryas, Bølling–Allerød Interstadial, Younger Dryas, Preboreal) as well as changes in organic matter inputs. Furthermore, decreases in the accumulation rate characterised minor short‐lived cooling events, such as Older Dryas event or Gerzensee oscillation. However, the Preboreal oscillation, which was well registered by other proxies at Lake Lautrey, could not be recognised in the testate amoeba record. This work demonstrates that lacustrine testate amoebae can be used for palaeoclimatic and palaeoecological reconstructions. Nevertheless, a better understanding of the relation between climate, organic matter and lacustrine testate amoebae requires further high‐resolution studies based on multi‐proxy approaches and the development of appropriate modern analogues. Copyright © 2010 John Wiley & Sons, Ltd.     

Peat multi-proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia

Sillasoo, Ü., Mauquoy, D., Blundell, A., Charman, D., Blaauw, M., Daniell, J. R. G., Toms, P., Newberry, J., Chambers, F M. & Karofeld, E. 2007 (January): Peat multi‐proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia. Boreas, Vol. 36, pp. 20–37. Oslo. ISSN 0300–9483. As part of a wider project on European climate change over the past 4500 years, a 4.5‐m peat core was taken from a lawn microform on Männikjärve bog, Estonia. Several methods were used to yield proxy‐climate data: (i) a quadrat and leaf‐count method for plant macrofossil data, (ii) testate amoebae analysis, and (iii) colorimetric determination of peat humification. These data are provided with an exceptionally high resolution and precise chronology. Changes in bog surface wetness were inferred using Detrended Correspondence Analysis (DCA) and zonation of macrofossil data, particularly concerning the occurrence of Sphagnum balticum, and a transfer function for water‐table depth for testate amoebae data. Based on the results, periods of high bog surface wetness appear to have occurred at c. 3100,3010–2990,2300, 1750–1610, 1510, 1410, 1110, 540 and 310 cal. yr BP, during four longer periods between c. 3170 and 2850 cal. yr BP, 2450 and 2000 cal. yr BP, 1770 and 1530 cal. yr BP and in the period from 880 cal. yr BP until the present. In the period between 1770 and 1530 cal. yr BP, the extension or initiation of a hollow microtope occurred, which corresponds with other research results from Mannikjarve bog. This and other changes towards increasing bog surface wetness may be the responses to colder temperatures and the predominance of a more continental climate in the region, which favoured the development of bog micro‐depressions and a complex bog microtopography. Located in the border zone of oceanic and continental climatic sectors, in an area almost without land uplift, this study site may provide valuable information about changes in palaeohydrological and palaeoclimatological conditions in the northern parts of the eastern Baltic Sea region.     

Climate change during the past 1000 years: a high‐temporal‐resolution multiproxy record from a mire in northern Finland

We present a record of peatland development in relation to climate changes and human activities from the Palomaa mire, a remote site in northern Finland. We used fine‐resolution and continuous sampling to analyse several proxies including pollen (for vegetation on and around the mire), testate amoebae (TA; for mire‐wetness changes), oxygen and carbon isotopes from Sphagnum cellulose (δ¹⁸O and δ¹³C; for humidity and temperature changes), peat‐accumulation rates and peat‐colour changes. In spite of an excellent accumulation model (30 ¹⁴C dates and estimated standard deviation of sample ages <1 year in the most recent part), the potential to determine cause–effect (or lead–lag) relationships between environmental changes and biotic responses is limited by proxy‐specific incorporation processes below the actively growing Sphagnum surface. Nevertheless, what emerges is that mire development was closely related to water‐table changes rather than to summer temperature and that water‐table decreases were associated with increasing peat‐accumulation rates and more abundant mire vegetation. A rapid fen‐to‐bog transition occurred within a few years around AD 1960 when the water table decreased beyond the historical minimum, supporting the notion that mires can rapidly shift into bogs in response to allogenic factors. Copyright © 2012 John Wiley & Sons, Ltd.     

Two decadally resolved records from north‐west European peat bogs show rapid climate changes associated with solar variability during the mid–late Holocene

Two ¹⁴C accelerator mass spectrometry (AMS) wiggle‐match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid–late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280–1300, cal. yr AD 1640 and cal. yr AD 1790–1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10–50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2–3 yr cm^?1, ～1310 yr old, 34 ¹⁴C dates) Danish profile offers an unprecedented high‐resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short‐lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yr cm^?1, ～5250 yr old, 42 ¹⁴C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.     

A multiproxy climate record from a raised bog in County Fermanagh,Northern Ireland: a critical examination of the link between bog surface wetness and solar variability

A proxy climate record from a raised bog in County Fermanagh, Northern Ireland, is presented. The record spans the interval between 2850 cal. yr BC and cal. yr AD 1000 and chronological control is achieved through the use of tephrochronology and ¹⁴C dating, including a wiggle‐match on one section of the record. Palaeoclimatic inferences are based on a combination of a testate amoebae‐derived water table reconstruction, peat humification and plant macrofossil analyses. This multiproxy approach enables proxy‐specific effects to be identified. Major wet shifts are registered in the proxies at ca. 1510 cal. yr BC, 750 cal. yr BC and cal. yr AD 470. Smaller magnitude shifts to wetter conditions are also recorded at ca. 380 cal. yr BC, 150 cal. yr BC, cal. yr AD 180, and cal. yr AD 690. It is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest Europe. Harmonic analysis of the proxies illustrates statistically significant periodicities of 580, 423–373, 307 and 265 years that may be related to wider Holocene climate cycles. This paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing. Relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of fossil testate amoebae in Selisoo Bog,Estonia: local variability and implications for palaeoecological reconstructions in peatlands

Niinemets, E., Pensa, M. & Charman, D. J. 2010: Analysis of fossil testate amoebae in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands. Boreas, 10.1111/j.1502‐3885.2010.00188.x. ISSN 0300‐9483. Local variability in decadal water‐table changes on an ombrotrophic peatland was explored using testate amoebae analysis of near‐surface peats in an Estonian raised bog. The distribution of testate amoebae assemblages was studied along the gradient from hummock to hollow in the upper 30‐cm layer of peat. As expected, testate amoebae assemblages in different micro‐ecotypes from hummock to hollow, even as close as 10 m apart, are distinctly different. Past water‐table change was reconstructed by applying a transfer function based on modern samples from throughout Europe. Results show a decline in water level from the mid‐late 20th century on Selisoo bog in all profiles from the different micro‐ecotypes. However, the absolute water‐table depths and amplitudes of fluctuations vary between reconstructions from different sampling micro‐ecotypes. Cores were correlated using changes in non‐mire pollen concentrations down‐core, but it was not possible to correlate minor changes in water‐table owing to non‐contiguous sampling and variable accumulation rates. We conclude that different microtopes show the same decadal trends in relative water‐table change but that the absolute magnitude of change may be more variable locally. It is important that reconstructed palaeohydrological changes in bogs consider changes in bog micro‐ecotypes, and their variation over time, as this may alter the sensitivity of an individual record to drivers such as climate change. Comparison and compilation of data from parallel cores from different micro‐ecotypes and/or different sites are likely to provide more robust reconstructions.     

A near‐annual palaeohydrological study based on testate amoebae from a sub‐alpine mire: surface wetness and the role of climate during the instrumental period

We present the first testate amoeba‐based palaeohydrological reconstruction from the Swiss Alps, and the first depth to the water table (DWT) calibration dataset for this region. Compared to existing models, our new calibration dataset performs well (RMSEP = 4.88), despite the length of the water table gradient covered (53 cm). The present‐day topography and vegetation of the study mire Mauntschas suggest that it is partly ombrotrophic (large Sphagnum fuscum hummocks, one of which was the coring site) but mostly under the minerotrophic influence of springs in the mire and runoff from the surrounding area. Ombrotrophic Sphagnum fuscum hummocks developed at the sampling site only during the last 50 years, when testate amoebae indicate a shift towards dry and/or acid conditions. Prior to AD 1950 the water table was much higher, suggesting that the influence of the mineral‐rich water prevented the development of ombrotrophic hummocks. The reconstructed DWT correlated with Pinus cembra pollen accumulation rates, suggesting that testate amoebae living on the mire and P. cembra growing outside of it partly respond to the same factor(s). Finally, temperature trends from the nearby meteorological station paralleled trends in reconstructed DWT. However, contrary to other studies made on raised bogs of northwestern Europe, the highest correlation was observed for winter temperature, despite the fact that testate amoebae would more logically respond to moisture conditions during the growing season. The observed correlation with winter temperature might reflect a control of winter severity on surface moisture during at least the first part of the growing season, through snow melt and soil frost phenomena influencing run‐off. More ecohydrological work on sub‐alpine mires is needed to understand the relationships between climate, testate amoebae and peatland development. Copyright © 2009 John Wiley & Sons, Ltd.     

The influence of vegetation composition on peat humification: implications for palaeoclimatic studies

Peat humification analysis is a widely used palaeoclimate proxy. However, recent studies combining humification with other proxies of mire surface wetness have identified inconsistencies between the records. We illustrate this inconsistency by comparing humification records with plant macrofossil profiles in three ombrotrophic bogs. Peat humification is a measure for organic decay and reflects changing palaeohydrological conditions and former vegetation composition. The resulting signal is considered to be a derived response to climate. However, even minor changes in the botanical composition of the peat may have a significant influence on humification measurements. The implications of this for palaeoclimate studies are discussed. The assumption that climate has been the major influence on variations in humification rests on the botanical composition being relatively homogeneous throughout the peat profile, and is therefore questionable. Consideration should be given to developing species-specific measures of humification and to testing the assumption that the major influence on peat humification is the surface wetness of the bog (and therefore climate).     

Surface wetness and mire development during the late Holocene in central Sweden

Andersson, S. & Schoning, K. 2010: Surface wetness and mire development during the late Holocene in central Sweden. Boreas, Vol. 39, pp. 749–760. 10.1111/j.1502‐3885.2010.00157.x. ISSN 0300‐9483. Late Holocene mire development and surface wetness changes have been studied in a small mixed mire located in central Sweden. Today the mire is characterized by a mainly ombrotrophic centre dominated by Sphagnum mosses, with Carex content increasing towards the more minerotrophic mire margins. Two peat sequences extracted from the central ombrotrophic part were investigated for stratigraphy, humification, testate amoebae analysis, C/N ratio and δ¹³C and δ¹⁵N stable isotopes. Three main stages of mire development are identified, with the first stage, between c. 4200 and 2600 cal. yr BP, characterized by water‐logged conditions, suggesting a minerotrophic fen stage. The second stage, between c. 2600 and 1000 cal. yr BP, is characterized by more ombrotrophic conditions and Sphagnum‐dominated vegetation. The onset of the prominent change at c. 2600 cal. yr BP could have been initiated by climate change coincident with a change in solar activity. The last stage, between c. 1000 and 50 cal. yr BP, is dominated by more ombrotrophic conditions, suggesting increased precipitation. This study shows that the response of hydrological proxies in a mixed mire during its development towards more ombrotrophic conditions might result in conflicting results, a finding that needs to be considered in palaeoenvironmental reconstructions from mires that change between ombrotrophic and minerotrophic settings.     

长白山区泥炭地现代有壳变形虫环境意义探讨

有壳变形虫(testate amoebae)是一种新的具有潜力的环境变化生物指标。对采集自长白山区哈泥(42°12′50″N,126°31′05″E)、金川(42°20′47″N,126°21′35″E)、赤池(42°03′16″N,128°03′22″E)和圆池(42°01′55″N,128°25′58″E)等4个泥炭地不同生境的75个有壳变形虫样品,采用冗余分析方法(RDA)研究有壳变形虫种类组合变化与7个环境变量的关系,所有采样点均以泥炭藓(Sphagnum)为优势植被。结果表明水位埋深(depth to water table),pH值和泥炭湿度是影响长白山区泥炭地有壳变形虫种类变化的主要环境因子,显著性检验达到p＜0.001的水平。这一结果与国外其他地区的研究结果相一致,这3个环境因子可以作为目标变量进行有壳变形虫－环境因子转换函数的构建。     

A replicated 3000 yr proxy-climate record from Coom Rigg Moss and Felecia Moss,the Border Mires,northern England

Quantitative plant macrofossil and colorimetric humification analyses have been used to reconstruct proxy-climate from two paired ombrotrophic bogs in northern England (Coom Rigg Moss and Felecia Moss). Detrended correspondence analysis was used to transform the raw floral data into indices of mire surface wetness. The chronology of each peat profile was determined by radiocarbon assay, supported by pollen correlations. Palaeoclimatic reconstructions have been made by linking documented historical changes in climate, and other proxy-climate records, to those inferred from the sites investigated in the study region. Both sites contain a sensitive palaeoclimatic record, as ten periods of increased effective precipitation have been detected between ca. cal. ad 1770–1800, ad 1400–1470, ad 1110–1260, ad 920–1060, ad 550–670, ad 210–360, 30 bc to ad 80, 180–130 bc, 590–520 bc and 760–710 bc. Copyright © 1999 John Wiley & Sons, Ltd.     

A 2800-year palaeoclimatic record from Tore Hill Moss,Strathspey, Scotland: the need for a multi-proxy approach to peat-based climate reconstructions

Analyses of plant macrofossils, testate amoebae and humification have been carried out on a 2800-year core from Tore Hill Moss, a raised bog in the Strathspey region of Scotland. All three analyses were carried out at the same 4 cm intervals allowing exact correlation, and the core was dated by nine Accelerator mass spectrometry radiocarbon dates and the Glen Garry tephra layer. The results have been combined and compared to present a bog surface wetness (BSW) record within which the limitations of each proxy method can be assessed and this has highlighted the advantages of a combined rather than a single proxy approach. Significant wet shifts are recorded at ca cal. 560 BC, 60 BC, AD 430, AD 570, AD 700, AD 1090 and AD 1640. Significant shifts to drier periods are also suggested ca cal. AD 220, AD 500 and AD 820. Some of the recorded shifts and phases are related to phases of wetter and drier climate such as the Sub-boreal/Sub-atlantic transition, the Dark Age deterioration and the Romano-British Warm Period. The Dark Ages are notable as a period of rapid peat accumulation and frequent water table fluctuations. Time-series analysis revealed a significant wet-shift cycle of 560 years from the testate amoebae data.     

Can testate amoeba‐based palaeohydrology be extended to fens?

Numerous palaeoecological studies have used testate amoeba analysis to reconstruct Holocene hydrological change in peatlands, and thereby past climatic change. Current studies have been almost exclusively restricted to ombrotrophic bogs and the period since the fen–bog transition. Although the critical link between peatland surface wetness and climate is less direct in minerotrophic peatlands, such records may still be of value where there are few others, particularly if multiple records can be derived and inter‐compared. Expanding the temporal and spatial scope of testate amoeba‐based palaeohydrology to minerotrophic peatlands requires studies to establish the primacy of hydrology and the efficacy of transfer functions across a range of sites. This study analyses testate amoeba data from wetlands spanning the trophic gradient in the eastern Mediterranean region. Results demonstrate that different types of wetlands have distinctly different amoeba communities, but hydrology remains the most important environmental control (despite water table depth being measured at different times for different sites). Interestingly, Zn and Fe emerge as significant environmental variables in a subset of sites with geochemical data. Testate amoeba–hydrology transfer functions perform well in cross‐validation but frequently perform poorly when applied to other sites, particularly with sites of a different nutrient status. It may be valid to use testate amoebae to reconstruct hydrological change from minerotrophic peatlands with an applicable transfer function; however, it may not be appropriate to use testate amoebae to reconstruct hydrological change through periods of ecosystem evolution, particularly the fen–bog transition. In practice, the preservation of amoeba shells is likely to be a key problem for palaeoecological reconstruction from fens. Copyright © 2010 John Wiley & Sons, Ltd.     

Multiproxy surface wetness records from replicate cores on an ombrotrophic mire: implications for Holocene palaeoclimate records

Ombrotrophic mires can provide records of palaeoclimate over the mid- to late- Holocene in several areas of the world. Their potential is currently partly limited by difficulties with scaling indices based on plant macrofossils and humification, and the need to account for the internal variability of the mire system. This paper explores the use of testate amoebae analysis as a third technique and assesses the minimum within-site variability by comparing results from two closely spaced cores. Reconstruction of surface wetness changes was carried out on cores from the centre of an intermediate raised-blanket mire, Coom Rigg Moss, Northumberland, by analysis of testate amoebae, plant macrofossils and humification. Surface wetness changes were expressed as mean annual water table changes inferred from testate amoebae assemblages, two separate indices based on plant macrofossils and percentage transmission of humification extracts. Comparisons between the proxies suggest good agreement of general trends in Sphagnum peats but some differences in monocot and ericaceous peats. The magnitude of surface wetness changes also differs within Sphagnum peats. The records from the separate cores converge over time and replicability between cores is best in the last 1000 yr. Changes over this period are similar to those shown by estimates based on documentary sources. Good agreement is obtained between a normalised plant macrofossil index and normalised reconstructed water-table values and it is suggested that this approach could form the basis for improved composite, multiproxy records from peatlands. Copyright © 1999 John Wiley & Sons, Ltd.     

Multiproxy analysis of inception and development of the Lac‐à‐la‐Tortue peatland complex,St Lawrence Lowlands,eastern Canada

The initial conditions for the development of a large peatland complex in the St Lawrence Lowlands were reconstructed to increase the understanding of early development and expansion modes in this region. Peatland basin morphometry was identified by creating a model based on over 1500 existing peat depth measurements, and six cores were extracted along transects from a central (deepest) location towards the margins. C accumulation rates and ecohydrological conditions were reconstructed from plant macrofossils, testate amoeba assemblages and ¹⁴C chronologies. Luminescence dating was performed to better delineate the timing of dune stabilization in the area and potentially related climate changes. Shallow freshwater plant communities acted as nuclei for the development of a rich minerotrophic fen around 10 300 cal. a BP in the deepest part of a shallow depression at the surface of the St‐Maurice river delta. Peat inception was followed by the paludification of peripheral parabolic dune systems. Luminescence dating suggested dune stabilization between 11 500 and 10 900 years ago. The initial rich fen persisted until 9500 cal. a BP, and was replaced by a poor fen dominated by sedges as a result of a decrease in mineral nutrient influx from upland runoff. The shift to ombrotrophic conditions in the oldest section of Lac‐à‐la‐Tortue peatland started around 5150 cal. a BP. This major ecohydrological change coincides with those observed in several other peatlands in southern Québec. Variations in carbon and peat accumulation rates in both ombrotrophic and minerotrophic sectors appear to have been primarily controlled by hydroseral succession, peat‐forming vegetation, hydrological conditions, topography and fire activity. This study is the first to provide a quantification of the total carbon pool of a peatland complex in southern Québec at 6.39 Mt C, corresponding to a mean C mass per area of 96.9 kg C m⁻² (σ = 50.60 kg C m⁻²).     

Tephra‐linked peat humification records from Irish ombrotrophic bogs question nature of solar forcing at 850 cal. yr BC

This paper investigates evidence for palaeoclimatic changes during the period ca. 1500–500 cal. yr BC through peat humification studies on seven Irish ombrotrophic bogs. The sites are well‐correlated by the identification of three mid‐first millennium BC tephras, which enable the humification records at specific points in time to be directly compared. Phases of temporarily increased wetness are suggested at ca. 1300–1250 cal. yr BC , ca. 1150–1050 cal. yr BC , ca. 940 cal. yr BC and ca. 740 cal. yr BC . The last of these is confirmed to be synchronous at five sites, suggesting external forcing on a regional scale. The timing of this wet‐shift is constrained by two closely dated tephras and is demonstrated to be distinct from the widely reported changes to cooler/wetter conditions associated with a solar minimum at 850–760 cal. yr BC , at which time the Irish sites appear instead to experience drier conditions. The results suggest the possibility of either non‐uniform responses to solar forcing in northwest Europe at this time, or the existence of unrelated climate events in the early first millennium BC . The findings caution against the correlation of loosely dated palaeoclimate data if the effects of forcing mechanisms are to be understood. Copyright © 2006 John Wiley & Sons, Ltd.