Stalagmite luminescence and peat humification records of palaeomoisture for the last 2500 years

Recent research has suggested that both raised and blanket bogs can provide proxy climate signals from variations in peat humification. In particular, oceanic margin sites have provided sensitive records that demonstrate century scale variations in humification. However, previous research has not compared records of peat humification with other terrestrial palaeoclimate proxies. Here, two records of climate change from an oceanic marginal site in NW Scotland are analysed. One, from a blanket bog, is derived from peat humification and covers the period 2100–100 BP. A second, from two stalagmites in a cave overlain by the bog, is derived from stalagmite luminescence wavelength variations for the samples deposited over 2500–0 BP. Both peat humification and stalagmite luminescence records demonstrate 90–100 year oscillations in bog wetness, that are attributed to variations in rainfall intensity or totals over this time period. It is argued that this is probably generated by a southward shift of the path of northern hemisphere depression tracks, possibly linked to variations in solar output

Surface age, ecosystem development, and C isotope signatures of respired CO2 in an alpine environment, north Iceland

We studied the late Holocene foreland and adjacent unglaciated terrain of a small cirque glacier system in north Iceland to explore the relationship between soil/ surface age, vegetation and soil evolution, and C isotope signatures of respired CO2 Field-based sampling of respired CO2 from vegetation/soil monoliths across the chronosequence was used as the basis for an analysis of the 12C:13C:14C atom ratios of CO2 using Isotope Ratio Mass Spectrometry (IRMS) and Accelerator Mass Spectrometry (AMS). Residual soil organic matter (SOM) fractions (humic and humin) were also 14C-dated from each of the surfaces, vegetation described, and soil C and N contents analyzed. Our major conclusions are (1) that ecosystem respiration in this mid-alpine environment is strongly dominated by "young" C and is not related to the 14C age of residual SOM fractions; (2) δ13C values of respired CO2, by contrast, do vary both with age of surface and with absolute respiration rate, but there is no clear indication of any effects mediated by plant species and functional type and/or the degree of reworking of SOM by decomposer organisms; and (3) the 14C dating of residual SOM fractions, together with the soil profile characteristics (including tephra deposits) and vegetation cover, both suggest some radical disturbance in soil development and SOM formation at Site 1 (the oldest surface studied here), and no clear signs of classical succession when comparing Sites 1 to 3. Finally, in the light of these observations, the familiar concept of chronosequences, and the predictable processes of ecosystem development that they often imply, are challenged in a mid-alpine tundra setting where recent climate change and anthropogenic influences (e.g., grazing pressure) are superimposed upon time as an ecological factor

Late Quaternary speleothem pollen in the British isles

As with many terrestrial areas, the British Quaternary sequence is characterised by incomplete, fragmentary records, whose correlation is based on stratigraphic or biostratigraphic techniques due to the lack of radiometric ages beyond the similar to 40 kyr limit of C-14 dating. Speleothems (secondary cave calcite deposits) offer a significant advantage over many sources of palaeoenvironmental information; they can be dated to a high precision and accuracy by uranium-thorium (U-238-Th-230) thermal ionisation and inductively coupled plasma (ICP) mass spectrometry in the time period back to 500 kyr. They may also contain sufficient well-preserved pollen representative of contemporary vegetation above the cave to allow palaeoenvironmental reconstruction. This study adopts the novel approach of combining pollen and thermal ionisation mass spectrometric (TIMS) U-Th dating of British speleothems to produce well-constrained palaeoenvironmental records. We report for the first time precisely dated records of pollen assemblages from speleothems suggesting the presence of thermophilous arboreal species in phases previously considered to have been consistently cool or cold and devoid of trees. Copyright (C) 2007 John Wiley &amp; Sons, Ltd.</p

The use of modelling and simulation approach in reconstructing past landscapes from fossil pollen data: a review and results from the POLLANDCAL network

Information on past land cover in terms of absolute areas of different landscape units (forest, open land, pasture land, cultivated land, etc.) at local to regional scales is needed to test hypotheses and answer questions related to climate change (e.g. feedbacks effects of land-cover change), archaeological research, and nature conservancy (e.g. management strategy). The palaeoecological technique best suited to achieve quantitative reconstruction of past vegetation is pollen analysis. A simulation approach developed by Sugita (the computer model POLLSCAPE) which uses models based on the theory of pollen analysis is presented together with examples of application. POLLSCAPE has been adopted as the central tool for POLLANDCAL (POLlen/LANdscape CALibration), an international research network focusing on this topic. The theory behind models of the pollen–vegetation relationship and POLLSCAPE is reviewed. The two model outputs which receive greatest attention in this paper are the relevant source area of pollen (RSAP) and pollen loading in mires and lakes. Six examples of application of POLLSCAPE are presented, each of which explores a possible use of the POLLANDCAL tools and a means of validating or evaluating the models with empirical data. The landscape and vegetation factors influencing the size of the RSAP, the importance of pollen productivity estimates (PPEs) for the model outputs, the detection of small and rare patches of plant taxa in pollen records, and quantitative reconstructions of past vegetation and landscapes are discussed on the basis of these examples. The simulation approach is seen to be useful both for exploring different vegetation/landscape scenarios and for refuting hypotheses