Keith Barber

A sensitive high-resolution record of late Holocene climatic change from a raised bog in northern England

Proxy-climatic data in the form of plant macrofossils have been analysed from a 5 m core from Bolton Fell Moss, Cumbria, UK. Detailed analysis of peat from the upper 50 cm of this core is used to demonstrate a strong correlation between changes in the relative proportion of taxa and known climatic changes over the last 1000 years. The record of changes in bog vegetation contained within the peat profile is used to reconstruct changes in bog-surface wetness for the latter half of the Holocene. As bog- surface wetness is directly controlled by the prevailing climatic conditions, this reconstruction can be viewed as a proxy-climate record. Twelve radiocarbon age estimates on the 5m core suggest that between 50 and 500 cm peat accumulated at a relatively constant rate of 12.4 yr cm-1 . The regular sampling intervals thus provide a time series of past bog-surface wetness; spectral analyses of this series indicates that wetness changes are cyclic, with a ca. 800 year periodicity.

Mire-development pathways and palaeoclimatic records from a full Holocene peat archive at Walton Moss, Cumbria, England.

Plant macrofossil data have been used to identify the successive mire communities occupying both central and marginal locations in the Walton Moss peatland complex, during the last 10 500 years. The reconstructed pathways of mire development indicate that early-Holocene fen and fen-carr communities were succeeded by species indicative of deep mire water tables and oligotrophic conditions. The character of the fen/bog transition (FBT) is compared with similar records of peatland development from Britain and Scandinavia and with independent climate data for the early Holocene. The ‘pseudohochmoor’ of central Europe is suggested as an approximate modern analogue for the dry pioneer oligotrophic mire type and alternative explanations for its presence are explored. The first major increase in ombrotrophic Sphagna occurred at c. 7800 cal. BP. Overlying Sphagnum peats provide a continuous record of climate change, inferred from fluctuations in raised mire surface wetness. The proxy palaeoclimate record, reconstructed using Detrended Correspondence Analysis, registers wet shifts commencing at c. 7800, c. 5300, 4410–3990 (2s range), c. 3500, 3170–2860 (2s range), 2320–2040 (2s range), c. 1750, c. 1450, c. 300 and c. 100 cal. BP. This climate record is compared with a similar one from Bolton Fell Moss and spectral analysis of the time-series gives periodicities of c. 1100 years and c. 600 years between wet shifts.

Holocene palaeoclimates from peat stratigraphy: macrofossil proxy climate records from three oceanic raised bogs in England and Ireland

Quantified analyses of plant macrofossil remains have been made from three profiles of peat from raised bogs spanning a distance of 425 km from western Ireland to northern England. The reconstructed vegetation of each profile is related to changing bog surface wetness (BSW), and since the bogs are ombrotrophic these BSW changes are interpreted in terms of changing climate. Using age/depth models based on a total of 49 radiocarbon dates a number of wetter and drier phases are identified, and phase-shifts to wetter and/or cooler climates are defined. Prominent coincident changes to wetter conditions are dated in at least two of the profiles to ca 4400–4000, 1750, 1400, and 1000 cal. BP and in all three profiles at 3200, 2750–2350, 2250, and around 700 cal. BP. These phases are related to proxy climate changes in other terrestrial data sets from northwest Europe and a broad degree of synchroneity is demonstrated.

Lipid biomarker, δ13C and plant macrofossil stratigraphy of a Scottish montane peat bog over the last two millennia

Abstract Seven horizons of a peat core covering the last 2000 years from Moine Mhor, a blanket bog in the Cairngorm Mountains, Scotland have been examined for the carbon number distributions of the long-chain hydrocarbon, alcohol and acid components using gas chromatography (GC) and gas chromatography—mass spectrometry (GC—MS). Compound specific δ 13 C values for individual n -alkanes were obtained, using gas chromatography—isotope ratio mass spectrometry (GC—irms). The lipid biomarker distributions and the δ 13 C values have been compared with those of eleven species of living plant dominant at the contemporary surface of the bog. The observed lipid stratigraphy shows only partial agreement with that calculated using macrofossil abundance data and the lipid distributions for the living taxa, a result which reflects the inherent uncertainties in both the lipid biomarker and the macrofossil approaches to palaeoenvironmental stratigraphy. The carbon isotope values for the individual n -alkanes of the plants (−27.6 to −36.6‰) and of the peat layers (−29 to −31.7‰) are as expected for the C 3 photosynthetic pathway. However, the n -alkanes from the surface samples were more depleted (by ∼2‰) in 13 C than those from the rest of the core, a negative shift which may, in part, reflect the shift (−1.2‰) in δ 13 C estimated for CO 2 in a pre-industrialised to an industrialised atmosphere.

A Database and Synthesis of Northern Peatland Soil Properties and Holocene Carbon and Nitrogen Accumulation

Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45°N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 ± 3% (standard deviation) for Sphagnum peat, 51 ± 2% for non-Sphagnum peat, and at 49 ± 2% overall. Dry bulk density averaged 0.12 ± 0.07 g/cm3, organic matter bulk density averaged 0.11 ± 0.05 g/cm3, and total carbon content in peat averaged 47 ± 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 ± 2 (standard error of mean) g C/m2/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25–28 g C/m2/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.

A 5500-year proxy-climate and vegetation record from blanket mire at Talla Moss, Borders, Scotland:

A monolith of peat taken from an upland blanket mire at Talla Moss, southern Scotland, was sub jected to peat humification and pollen analyses to produce both a proxy-climate record and a vegetational history covering the last 5500 years. While the peat showed little visible stratigraphy, with no intimation of major peat humification changes, colorimetric data indicate a markedly oscillatory climate record, which is apparently largely independent of, or out of phase with, major vegetational changes. The raw data imply particular wet shifts in climate at c. 3455 BP, c. 2600 BP, c. 1930 BP, c. 1095 BP, with a markedly wet (or cool and wet) episode commencing at c. 540 BP. (These are central age estimates, and should not be regarded as precise dates for the inferred climate shifts.) Other wet shifts apparently date from c. 3070 BP, c. 2265 BP and c. 1700 BP, although the first of these corresponds with pollen evidence for significant prehistoric human activity in the locality. Spectral analysis of the peat humification data, when expressed on an interpolated calibrated age-scale, suggests a cycle of c. 210 years; this is dependent on the accuracy of the radiocarbon chronology and should be treated with caution. The upland site is amenable to tephrochronology, which, if also applied to ombrotrophic mire sites elsewhere, might then permit more precise correlation and comparisons of proxy-climate data between sites.

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.

Replicability and variability of the recent macrofossil and proxy-climate record from raised bogs: field stratigraphy and macrofossil data from Bolton Fell Moss and Walton Moss, Cumbria, England

Replication of results is a basic tenet of science, but in palaeoecology this is very time-consuming and the ‘signal’ is subject to ‘noise’. The derivation of proxy-climate signals from ombrotrophic peat was carried out originally using samples from open peat faces where the stratigraphic relationships could be easily observed. Now that such sections are rare and often degraded there is a need to demonstrate that data can be replicated from core profiles. Ten short cores taken from two adjacent bogs have been analysed for macrofossils and show a coherent series of changes, which are also similar to previous profiles from the same sites. It is concluded that variation between profiles is slight and less than observations of present vegetation mosaics might suggest. Recommendations for a standard approach to fieldwork on raised bogs that emphasises the utility of subfossil pool layers are proposed and the need for a secure chronology is stressed.

Replicated proxy-climate signals over the last 2000 yr from two distant UK peat bogs: new evidence for regional palaeoclimate teleconnections

Ombrotrophic peat is an established source of proxy-climate data but previous records have been produced by different methods and have been difficult to compare. High-resolution plant macrofossil analysis has been applied to a lowland raised bog at Fallahogy, Northern Ireland, and a montane blanket bog, Moine Mhor in the Cairngorms, Scotland. Although the bogs are 300 km apart and differ floristically, the results demonstrate parallel responses to climatic forcing, especially that of the Little Ice Age. This approach provides a powerful tool for reconstructing proxy-climate records wherever suitable peat deposits exist. In contrast to the ocean and ice core records these proxies are from a terrestrial source, and related to climate changes on land over most of the Holocene.

Peatlands as scientific archives of past biodiversity

Peat bogs preserve past biodiversity in a way which is unique among ecosystems, but the full realization of this, and the exploitation of the various records which are archived in the stratified layers of peat, is only now beginning. Present knowledge of peat formation in ombrotrophic or rain-fed bogs is reviewed and the many advantages of such systems as proxy-data sources are summarized. Some results of recent work involving pollen analysis and human impact, pollution histories, volcanic ash layers, plant macrofossils and the prospects for a detailed proxy-climate record are presented. The present vegetation of such bogs is only a very partial view of their past biodiversity; the conservation of the peat that remains must have a high priority.