A cold but stable 4,200 yr event in Britain and the northeastern Atlantic region

Abstract

The existence of an abrupt cold event in the British Isles at ca 4200 years before AD1950 (cal. yr BP) is investigated through analysis of the oxygen and carbon isotope value (δ¹⁸O and δ¹³C) of annually laminated, seasonally precipitated lake carbonates from the lake of Diss Mere in eastern England. Modern rainfall and lake water isotope data indicate that evaporation is a major control on the isotope value of modern lake waters, consistent with Diss Mere's current status as a small (0.0034 km²) and shallow (<6m), closed lake system. However, both the characteristics of isotope data from the interval 4700 to 3700 cal yr BP and the greater depth of the lake basin at that time (>15m water) indicates that whilst evaporation still operated, major shifts in δ¹⁸O values most likely reflect shifts in patterns of atmospheric circulation (primarily through air mass trajectory, air temperature and precipitation amount). A centennial-scale interval of persistently low δ¹⁸O values occurred between ca 4320 and 4210 cal yr BP and is interpreted as a cold event with changes in the elemental composition of the sediments supporting this interpretation. Correlation of this record with other sequences from the North Atlantic and western Europe, either through comparison of independent chronologies or age markers such as the Hekla 4 tephra, indicates that this event was well expressed across this region and was characterised by changes in temperature, storminess and ocean/atmospheric circulation. It is argued that increasing evidence exists for an abrupt event in this region at ca 4200 cal yr BP, but it is the high-resolution nature of the Diss Mere sequence and the regionally extensive tephras that this record contains that allows the timing and character of this event to be understood.