Chronologies for recent peat deposits using wiggle-matched radiocarbon ages: problems with old carbon contamination

Reproduced with permission of the publisher. © 2005 by the Arizona Board of Regents of behalf of the University of Arizona.Dating sediments which have accumulated over the last few hundred years is critical to the calibration of longer-term paleoclimate records with instrumental climate data. We attempted to use wiggle-matched radiocarbon ages to date 2 peat profiles from northern England which have high-resolution records of paleomoisture variability over the last ~300 yr. A total of 65 14C accelerator mass spectrometry (AMS) measurements were made on 33 macrofossil samples. A number of the age estimates were older than expected and some of the oldest ages occurred in the upper parts of the sequence, which had been dated to the late 19th and early 20th century using other techniques. We suggest that the older 14C ages are the result of contamination by industrial pollution. Based on counts of spheroidal carbonaceous particles (SCPs), the potential aging effect for SCP carbon was calculated and shown to be appreciable for samples from the early 20th century. Ages corrected for this effect were still too old in some cases, which could be a result of fossil CO2 fixation, non-SCP particulate carbon, contamination due to imperfect cleaning of samples, or the “reservoir effect” from fixation of fossil carbon emanating from deeper peat layers. Wiggle matches based on the overall shape of the depth-14C relationship and the 14C minima in the calibration curve could still be identified. These were tested against other age estimates (210Pb, pollen, and SCPs) to provide new age-depth models for the profiles. New approaches are needed to measure the impact of industrially derived carbon on recent sediment ages to provide more secure chronologies over the last few hundred years

Distribution of testate amoebae in salt marshes along the North American East Coast

Reproduced with permission of the publisher. © 2006 Cushman Foundation for Foraminiferal ResearchThis study describes the distribution of testate amoebae in three North American East Coast salt marshes (Leipsic River marsh, Delaware, USA; Little River marsh, Maine, USA; and Little Dipper Harbour marsh, New Brunswick, Canada). Five zones are recognized in the high salt marsh. With increasing marine influence, these zones are characterized by the following succession of dominant taxa: Valkanovia elegans, Tracheleuglypha dentata, Centropyxis cassis type, C. platystoma type and Difflugia pristis type. Most species occur in all three marshes, and their general vertical distribution is comparable. The results are also comparable with those obtained from British salt marshes, suggesting that salt-marsh testate amoebae have similar distributions on both sides of the Atlantic Ocean. The precision of the sea-level indicative value of testate amoebae in fossil salt-marsh sediments is a function of the local mean tidal range (MTR). Results of this study show that testate amoebae can indicate former sea levels with a precision of ±0.04 m in the Leipsic River marsh (MTR = 1.75 m), ±0.09 m in the Little River marsh (MTR = 2.6 m), and ±0.18 m in the Little Dipper marsh (MTR = 5.8 m)

A Last Glacial Maximum Pollen Record from Bodmin Moor Showing a Possible Cryptic Northern Refugium in Southwest England

Reproduced with permission of the publisher. The definitive version is available at www3.interscience.wiley.com. Copyright © 2009 John Wiley & Sons, LtdA late Devensian palynological record is presented from Dozmary Pool (Bodmin Moor, southwest England), beyond the southern limit of the Last Glacial Maximum (LGM) British Ice Sheet. The pollen assemblages indicate predominantly herbaceous tundra steppe communities but also include elevated levels (typically 10-20%) of conifer tree pollen (Picea, Pinus, Abies) and lower but persistent percentages of broadleaf tree pollen during the LGM. This record is seemingly at odds with the orthodox view of an entirely treeless tundra steppe environment for this region and elimination of tree species from the British Isles during glacial maxima. Long-distance pollen transport seems an unlikely explanation for the tree pollen considering distance to the nearest known refugia, except possibly for Pinus. Reworking of the tree pollen, often invoked in these circumstances, remains a possible alternative, especially given the abundance of these trees in the region during early Devensian interstadials. However, this explanation has been challenged by studies reporting plant macrofossil and faunal evidence for survival of temperate biota during glacial maxima and from climate modelling work that suggests some trees could have survived the glacial extremes in areas well beyond the recorded glacial refugia. Assuming reworking was not a major factor, the Dozmary Pool pollen record is consistent with the "apos;cryptic northern refugia hypothesis"apos; that invokes survival of trees in small, scattered populations under locally favourable conditions during glacial maxima

Testate amoebae as palaeohydrological proxies in Sürmene Aǧaçbaşi Yaylasi Peatland (Northeast Turkey)

Testate amoebae as palaeohydrological proxies in sürmene ağaçbaşi yaylasi peatland (northeast Turkey) Testate amoebae are unicellular micro-organisms whose hydrological sensitivity and good preservation in peats make them valuable proxies for past peatland surface wetness, and therefore climate. Previous testate amoebae transfer functions have been spatially restricted with no studies from Asia. To derive a transfer function, a sequence of samples was extracted from an ombrotrophic peatland in Turkey and amoebae counted. The internal structure of the data was explored using principal components analysis and relationships with the environmental data tested by redundancy analyses. Transfer function models were developed using a variety of techniques. As in other regions, depth to water table is the most important control on amoebae community composition. Transfer function performance was initially poor, primarily due to the inclusion of samples from areas of the site that had been heavily affected by peat cutting and had distinctly different amoebae communities. Model performance is improved by selective sample exclusion, reducing jack-knifed root mean square error of prediction to 7.1 cm. The model was tested using an initial palaeoecological data-set. Overlap with the training set was limited, although a hydrological reconstruction using this model produces similar results to a transfer function derived from northern European peatlands. This study provides the first testate amoebae transfer function from Asia and demonstrates that hydrological preferences of many of the key taxa are consistent across a large area of the Northern Hemisphere. The transfer function will allow detailed palaeoclimate reconstruction from this peatland, adding to our knowledge of Holocene climatic change in southwest Asia

Reconstruction of recent sea-level change using testate amoebae

Reproduced with permission of the publisher. Copyright © 2009 University of Washington Published by Elsevier Inc.Proxy-based sea-level reconstructions place the instrumentally observed rates of recent sea-level rise in a longer term context by providing data that extend the instrumental sea-level record into past centuries. This paper presents the first sea-level reconstructions based on analyses of testate amoebae, to test their ability to produce high-precision reconstructions of past sea level. We present two reconstructions for the past 100 yr from sites in Maine (USA) and Nova Scotia (Canada) based on short cores from salt marshes, and modern training data from North America and the United Kingdom. These are compared with tide-gauge records and reconstructions based on foraminifera from the same cores. The reconstructions show good agreement with both the tide-gauge data and the foraminifera-based reconstructions. The UK data perform well in predicting known elevations of North American surface samples and produce sea-level reconstructions very similar to those based on the North American data, suggesting the methodology is robust across large geographical areas. We conclude that testate amoebae have the potential to provide robust, higher precision sea-level reconstructions for the past few centuries if modern transfer functions are improved and core sites are located within the main zone of testate amoebae occurrence on the salt marsh

Peatlands and Climate Change

This is the author's manuscript version and this version is free to view and download for personal use only. Not for re-distribution, re-sale or use in derivative works.This material is forthcoming in Peatland Restoration and Ecosystem Services Science, Policy and Practice, 9781107619708, © Cambridge University PressThe fundamental reason for the presence of peatlands is a positive balance between plant production and decomposition. Organic matter accumulates in these systems because prolonged waterlogged conditions result in soil anoxia (i.e., exclusion of oxygen), and under these conditions decomposition rates can be lower than those of primary production. Climate therefore plays an important role in peat accumulation, both directly by affecting productivity and decomposition processes, and indirectly through its effects on hydrology/water balance and vegetation (for a summary, refer to Yu, Beilman & Jones 2009). Climate provides broad-scale constraints or controls on peatland extent, types and vegetation, and ultimately, ecosystem functioning, carbon accumulation, greenhouse gas exchange and all of the other ecosystem services that peatlands provide. Peatlands can play a vital role in helping society mitigate and adapt to climate change, because of their carbon and water regulating functions, while at the same time, the climate sensitivity of peatlands makes them potentially vulnerable to future global warming and changes in spatial and temporal patterns of precipitation, especially if they are in a degraded state. Climate change is likely to alter the hydrology and soil temperature of peatlands, with far- reaching consequences for their biodiversity, ecology and biogeochemistry. Their involvement in the global carbon cycle will also be affected, with the possibility of drier conditions allowing peatland erosion and increases in CO2 emissions that would result in a positive feedback to climate change (Turetsky 2010). This highlights all the more the need for restoration to ensure peatlands are resilient to change so that they continue to deliver ecosystem services for human well-being. This chapter describes the interactions between climate and peatlands, in three sections. The first section explains how present climate influences peatlands, by documenting how climate limits peatland geographical extent globally, and how bioclimatic envelope models can predict peatland extent. We indicate how each type of peatland is linked to a specific climate range, and introduce the concept of ecosystem function in relation to climate. The second section looks into the past. It describes how peat preserves a record of past climates and environmental conditions that can be deciphered to reveal the history of peatland vegetation, hydrology and carbon accumulation changes in relation to past changes in climate. We highlight lessons that can be learned from the palaeorecord preserved in peat. The final section discusses the potential effects of present and future climate change on peatlands, their extent, carbon accumulation rates, fire frequency, water table and greenhouse gas exchanges. We also consider how increases in sea level and CO2 concentration, and decreases in the extent of permafrost, are likely to affect peatlands

Climate-driven expansion of blanket bogs in Britain during the Holocene

Blanket bog occupies approximately 6 % of the area of the UK today. The Holocene expansion of this hyperoceanic biome has previously been explained as a consequence of Neolithic forest clearance. However, the present distribution of blanket bog in Great Britain can be predicted accurately with a simple model (PeatStash) based on summer temperature and moisture index thresholds, and the same model correctly predicts the highly disjunct distribution of blanket bog worldwide. This finding suggests that climate, rather than land-use history, controls blanket-bog distribution in the UK and everywhere else. We set out to test this hypothesis for blanket bogs in the UK using bioclimate envelope modelling compared with a database of peat initiation age estimates. We used both pollen-based reconstructions and climate model simulations of climate changes between the mid-Holocene (6000 yr BP, 6 ka) and modern climate to drive PeatStash and predict areas of blanket bog. We compiled data on the timing of blanket-bog initiation, based on 228 age determinations at sites where peat directly overlies mineral soil. The model predicts large areas of northern Britain would have had blanket bog by 6000 yr BP, and the area suitable for peat growth extended to the south after this time. A similar pattern is shown by the basal peat ages and new blanket bog appeared over a larger area during the late Holocene, the greatest expansion being in Ireland, Wales and southwest England, as the model predicts. The expansion was driven by a summer cooling of about 2 °C, shown by both pollen-based reconstructions and climate models. The data show early Holocene (pre-Neolithic) blanket-bog initiation at over half of the sites in the core areas of Scotland, and northern England. The temporal patterns and concurrence of the bioclimate model predictions and initiation data suggest that climate change provides a parsimonious explanation for the early Holocene distribution and later expansion of blanket bogs in the UK, and it is not necessary to invoke anthropogenic activity as a driver of this major landscape change

Aeolian sediment reconstructions from the Scottish Outer Hebrides: Late Holocene storminess and the role of the North Atlantic Oscillation

Northern Europe can be strongly influenced by winter storms driven by the North Atlantic Oscillation (NAO), with a positive NAO index associated with greater storminess in northern Europe. However, palaeoclimate reconstructions have suggested that the NAO-storminess relationship observed during the instrumental period is not consistent with the relationship over the last millennium, especially during the Little Ice Age (LIA), when it has been suggested that enhanced storminess occurred during a phase of persistent negative NAO. To assess this relationship over a longer time period, a storminess reconstruction from an NAO-sensitive area (the Outer Hebrides) is compared with Late Holocene NAO reconstructions. The patterns of storminess are inferred from aeolian sand deposits within two ombrotrophic peat bogs, with multiple cores and two locations used to distinguish the storminess signal from intra-site variability and local factors. The results suggest storminess increased after 1000 cal yrs BP, with higher storminess during the Medieval Climate Anomaly (MCA) than the LIA, supporting the hypothesis that the NAO-storminess relationship was consistent with the instrumental period. However the shift from a predominantly negative to positive NAO at c.2000 cal yrs BP preceded the increased storminess by 1000 years. We suggest that the long-term trends in storminess were caused by insolation changes, while oceanic forcing may have influenced millennial variability

Investigating the maximum resolution of µXRF core scanners: a 1800 year storminess reconstruction from the Outer Hebrides

Micro x-ray fluorescence (µXRF) core scanning is capable of measuring the elemental composition of lake sediment at sub-millimetre resolution, but bioturbation and physical mixing may degrade environmental signals at such fine scales. The aim of this research is to determine the maximum possible resolution at which meaningful environmental signals may be reconstructed from lake sediments using this method. Sediment from a coastal lake in the Outer Hebrides, Scotland, has been analysed using calibrated element measurements to reconstruct storminess since AD 200. We find that a Ca/K ratio in lake-core sediments reflects the presence of fine calcium carbonate shell fragments, a constituent of sand in the catchment that is washed and blown into the lake. Variations in this ratio are significantly correlated with instrumental records of precipitation and low pressures, suggesting it is a proxy for storminess. Furthermore, identification of a c. 60-year cycle supports a climatic influence on Ca/K, as this cycle is frequently identified in reconstructions of the North Atlantic Oscillation and North Atlantic sea-surface temperature. Comparison with weather records at different resolutions and spectral analysis indicate that µXRF data from Loch Hosta can be interpreted at sub-decadal resolutions (equivalent to core depth intervals of 3–5 mm in this location). Therefore, we suggest that sub-centimetre sampling using µXRF core scanning could be beneficial in producing environmental reconstructions in many lake settings where sediments are not varved

Spatial variation of hydroclimate in north-eastern North America during the last millennium

Climatic expressions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) vary regionally, with reconstructions often depicting complex spatial patterns of temperature and precipitation change. The characterisation of these spatial patterns helps advance understanding of hydroclimate variability and associated responses of human and natural systems to climate change. Many regions, including north-eastern North America, still lack well-resolved records of past hydrological change. Here, we reconstruct hydroclimatic change over the past millennium using testate amoeba-inferred peatland water table depth reconstructions obtained from fifteen peatlands across Maine, Nova Scotia, Newfoundland and Québec. Spatial comparisons of reconstructed water table depths reveal complex hydroclimatic patterns that varied over the last millennium. The records suggest a spatially divergent pattern across the region during the Medieval Climate Anomaly and the Little Ice Age. Southern peatlands were wetter during the Medieval Climate Anomaly, whilst northern and more continental sites were drier. There is no evidence at the multi-decadal sampling resolution of this study to indicate that Medieval mega-droughts recorded in the west and continental interior of North America extended to these peatlands in the north-east of the continent. Reconstructed Little Ice Age hydroclimate change was spatially variable rather than displaying a clear directional shift or latitudinal trends, which may relate to local temporary permafrost aggradation in northern sites, and reconstructed characteristics of some dry periods during the Little Ice Age are comparable with those reconstructed during the Medieval Climate Anomaly. The spatial hydroclimatic trends identified here suggest that over the last millennium, peatland moisture balance in north-eastern North America has been influenced by changes in the Polar Jet Stream, storm activities and sea surface temperatures in the North Atlantic as well as internal peatland dynamics