Disentangling the environmental signals recorded in Holocene calcite varves based on modern lake observations and annual sedimentary processes in Diss Mere, England

Diss Mere is a small natural lake located in the centre of the town Diss in Norfolk (England). The lake, which has been exposed to different stressors including climate variability and changing land use, has significant recreational, historical and environmental value. The Diss Mere sediments are annually-laminated for most of the Holocene (2.1–10.3 ka BP), which allows the study of the lake evolution and its response to changing environmental conditions at an exceptionally high resolution. As with many mid-latitude, alkaline lakes, Diss Mere’s sediments are formed of biogenic-calcite varves. We have conducted a 3.5-year lake-monitoring survey including sediment trapping to identify the main drivers and seasonal processes contributing to lake sedimentation. Our results demonstrate that the modern lake is still producing seasonally-differentiated sediments today, however, are unable to be preserved as varves due to the permanent oxygenation of the lake bottom through gradual lake shallowing. Seasonal sediment fluxes follow a general pattern of (i) an early spring-diatom bloom; (ii) spring precipitation of medium-coarse calcite grains; (iii) summer precipitation of smaller endogenic calcite grains; and (iv) an autumn algal bloom and endogenic calcite precipitation intermixed with benthic diatoms and micrite. Whilst calcite precipitates throughout the whole year, peaks are observed in the epilimnion during the summer. This study shows that a modern analogue approach can be applied to the varves revealing their potential for environmental and climate reconstruction and highlights the significance of monitoring surveys for modern analogue approaches to palaeolimnological research.