Updated age constraints on key tephra markers for NW Europe based on a high-precision varve lake chronology

Cryptotephra layers deposited in annually-laminated (varved) lake records can be precisely dated and used as a means to correlate archives, testing the spatio-temporal variability of climatic transitions, environmental change and human activity. The site of Diss Mere, East Anglia, is recognised for its high-precision chronology, which is varved through the period ∼2070–10,290 cal. BP. Here we present the results of further cryptotephra research from Diss Mere. Upon reinspection of these sediments and using the high-precision varve chronology to guide our investigation, we identified two, previously undescribed Icelandic cryptotephra layers in the Diss Mere record. The discovery of an important tephrostratigraphic marker, Hekla 4, extends the known ash dispersal from this eruption southwards and we provide an updated and highly resolved age for this key tephra of 4435 ± 16 cal. BP. Given the widespread distribution of this tephra layer in Northwest Europe, the Diss Mere record could be integrated into this tephrostratigraphic network, allowing precise comparison of palaeoenvironmental archives across Europe. The second addition to the Diss Mere tephrostratigraphy is a cryptotephra layer deriving from the Torfajökull volcanic system in Iceland, with an age of 7828 ± 39 cal. BP. At present, this tephra layer is yet to be identified elsewhere and adds complexity to the isochron assignment of Lairg A and Lairg B tephras in records.