The Caerwys tufa in North Wales (UK) contains basal deposits thought to represent carbonate precipitation during the Late-glacial interstadial. These deposits are used to test whether stable isotope data record all or part of a warming-cooling-warming trend through the transition of the Late-glacial interstadial, Younger Dryas stadial and early Holocene. The d18O values and molluscan abundance data suggest that deposition of the Late-glacial tufa occurred mainly during a relatively warm period (? GL-1c or 1e) followed by cooling, the latter likely to be the transition into the Younger Dryas stadial. Tufa deposition is not recorded in the coldest part of the stadial: it is replaced by a sandy horizon. d13C values around -8.5‰ in the basal Late-glacial interstadial tufas show there was a significant influence from isotopically light soil-zone CO2, consistent with development of birch scrub and woodland further south in North Wales. During climatic cooling into the Younger Dryas stadial a 1‰ decrease in tufa d13C is interpreted to represent decreasing phytoplankton photosynthetic activity in pools causing less isotopic enrichment of the tufa d13C. In the (pre-9000 cal. years BP) early Holocene tufas at Caerwys, palaeo-water temperatures calculated from d18O in tufa calcite and from shell carbonate of Lymnaea peregra agree well and suggest summer water temperatures in the range 13 to 16.5°C.d13C data from these early Holocene pool-micrite tufas demonstrate that phytoplanktonic photosynthetic activity within the water column resumed under the warmer conditions causing isotopic enrichment of the tufa d13C values.
|Number of pages||12|
|Publication status||Published - 2006|