Complexities in European Holocene cryptotephra dispersal revealed in the annually laminated lake record of Diss Mere, East Anglia

Abstract

Annually-laminated (varved) lake records serve as valuable archives for the study of subtle variations in the timing and expression of changing environmental and climatic conditions at sub-decadal resolution. Well-constrained, individual cryptotephras preserved within varved sediments can be precisely dated and allow the direct correlation of sites within which the same deposits are identified. Although varved sediments provide a dating ideal for cryptotephras, lakes with such records for the Holocene are rare. Here we present the first Holocene-age tephrostratigraphy from a varved record in the British Isles, comprising fifteen cryptotephra layers. The sedimentary record of Diss Mere spans the period ~2070–10,290 cal. BP and is linked to a varve chronology. Our analysis reveals two key findings. 1) We identify a series of four, geochemically indistinguishable cryptotephra layers of Hekla origin, for the first time, through a ca.960-year interval from ~7170–8130 cal. BP. These tephras match the Lairg A chemistry from Hekla and we therefore recommend caution must be taken if employing the Lairg A tephra as an isochron in records. 2) We identify one cryptotephra deposit which originates from an eruption in the Azores ~2310 cal. BP, marking it the first discovery of its kind in England. Our results demonstrate how the temporal expanse and well-resolved nature of varved records can provide a more complex narrative to eruptive histories and ash dispersal than previously established from proximal studies. This tephrostratigraphic record for Diss Mere extends the known distributions of the identified cryptotephras, highlighting the potential for sites in southern Britain to act as valuable tephra repositories.