Lacustrine oxygen isotopes as tracers of past climate change in NW Europe

The Holocene, although generally considered climatically stable in northwest Europe, is interrupted by abrupt changes. This research investigates the magnitude, expression and driving mechanisms of abrupt climatic change from lacustrine oxygen isotope records over the Early and Late Holocene. This is important in developing our understanding of climatic changes under varying driving mechanisms, and their impacts, considering the current climate crisis. The oxygen and carbon isotope analyses for the study were undertaken on ostracods, which are small aquatic crustaceans that have shells of low-Mg calcite. Emphasis was placed on the oxygen-isotope records in this research, the carbon-isotope data were used to provide supporting information. The Late Holocene was investigated at two neighbouring, extant, lake sites in Hampshire. A monitoring study was undertaken at each lake to help understand present-day water isotope systematics, in order to support the palaeoenvironmental reconstruction. Comparison of the proxy records from both lakes indicated each of them recorded broadly similar signals, although with some differences attributed to lake-specific processes. An Early Holocene record was produced from Crudale Meadow, Orkney Mainland. This record depicts a negative oxygen-isotope excursion dating to ~ 9.7 ka, which matches the expression and magnitude of abrupt climatic events in other lake sites in the British Isles and the Greenland ice core stratigraphy. The timing of the earliest Holocene oxygen isotope decline at Crudale Meadow, suggests asynchronicity with records across northwest Europe. Output from an isotope-enabled General Circulation Model, iHadCM3, was used to calculate synthetic carbonate oxygen-isotope values that were compared to the lake-sediment isotope data from both time intervals. iHadCM3 produces good representations of proxy data in these periods. This historical iHadCM3 data highlight the role of the North Atlantic Oscillation (NAO) in driving isotopic change in the British Isle