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.
When mollusc shells are analysed conventionally for amino acid geochronology, the entire population of amino acids is included, both inter- and intra-crystalline. This study investigates the utility of removing the amino acids that are most susceptible to environmental effects by isolating the fraction of amino acids encapsulated within mineral crystals of mollusc shells (intra-crystalline fraction). Bleaching, heating and leaching (diffusive loss) experiments were undertaken on modern and fossil Corbicula fluminalis, Margaritifera falcata, Bithynia tentaculata and Valvata piscinalis shells. Exposure of powdered mollusc shells to concentrated NaOCl for 48 h effectively reduced the amino acid content of the four taxa to a residual level, assumed to represent the intra-crystalline fraction. When heated in water at 140 °C for 24 h, only 1% of amino acids were leached from the intra-crystalline fraction of modern shells compared with 40% from whole shell. Free amino acids were more effectively retained in the intra-crystalline fraction, comprising 55% (compared with 18%) of the whole shell after 24 h at 140 °C. For fossil gastropods, the inter-shell variability in D/L values for the intra-crystalline fraction of a single-age population was reduced by 50% compared with conventionally analysed shells. In contrast, analysis of the intra-crystalline fraction of C. fluminalis does not appear to improve the results for this taxon, possibly due to variability in shell ultrastructure. Nonetheless, the intra-crystalline fraction in gastropods approximates a closed system of amino acids and appears to provide a superior subset of amino acids for geochronological applications.
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