Climatic change recorded by stable isotopes and trace elements in a British Holocene tufa

ER Garnett, JE Andrews, RC Preece, PF Dennis

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Abstract

Combined stable isotope (d18O and d13C) and trace element (Mg, Sr) geochemistry from bulk tufa calcite and ostracod shell calcite from an early Holocene British tufa reveal clear records of Holocene palaeoclimatic change. Variation in d18O is caused principally by change in the isotopic composition of Holocene rainfall (recharge), itself caused mainly by change in air temperature. The d13C variability through much of the deposit reflects increasing influence of soil-zone CO2, owing to progressive woodland soil development. Bulk tufa Mg/Ca and Sr/Ca are controlled by their concentrations in the spring water. Importantly, Mg/Ca ratios are not related to d18O values and thus show no temperature dependence. First-order sympathetic relationships between d13C values and Mg/Ca and Sr/Ca are controlled by aquifer processes (residence times, CO2 degassing and calcite dissolution/reprecipitation) and probably record intensity of palaeorainfall (recharge) effects. Stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data. The ostracod isotopic records are markedly ‘spiky’ because the ostracods record ‘snapshots’ of relatively short duration (years), whereas the bulk tufa samples record averages of longer time periods, probably decades. The d18O record appears to show early Holocene warming, a thermal maximum at ca. 8900?cal. yr?BP and the global 8200?yr BP cold event. Combined d13C, Mg/Ca and Sr/Ca data suggest that early Holocene warming was accompanied by decreasing rainfall intensity. The Mg/Ca data suggest that the 8200?yr BP cold event was also dry. Warmer and wetter conditions were re-established after the 8200?yr BP cold event until the top of the preserved tufa sequence at ca. 7100?cal. yr BP.
Original languageEnglish
Pages (from-to)251-262
Number of pages12
JournalJournal of Quaternary Science
Volume19
Issue number3
DOIs
Publication statusPublished - 2004

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