Is the ‘Year Without a Summer’ imprinted in continental varve thickness records?

The 1816 CE Year Without a Summer (YWS), following the 1815 CE Tambora eruption, is a classic example of a global cooling event caused by a volcanic eruption. It is well-documented in various historical sources and natural archives. In this study, we investigate whether imprints of this event can be detected in time series of varve and varve sublayer thickness (VT) derived from lake archives. To this end, we examine 43 published and globally distributed VT records covering the period 1766–1866 CE. We hypothesize that thickness anomalies in many VT records correspond to the YWS because it was one of the most prominent climatic events of recent centuries, and VT is a sensitive climate recorder. We evaluate site-specific temperature and precipitation anomalies for the YWS of each investigated lake using available climate model simulations that incorporate proxy and observational data. VT anomalies are identified based on individually selected threshold values for each record, following a robust estimation of trend and variability in the VT data. The climate variables and seasons most influential to VT are determined for each lake based on the related original publications. Our analysis documents that only five records reveal VT anomalies attributable to the YWS. The relationship between VT anomalies and the YWS is questionable in seven records, primarily due to uncertainty about the climatic influence on VT in these cases, and unlikely for the remaining 31 records. The 31 records lacking a YWS signature are divided into two groups. In the first group, the absence of VT anomalies is likely due to weak climate forcing, as temperature and precipitation changed only slightly at those locations. In the second group, while climate forcing was significant, the season during which the anomaly occurred or the specific climate variable that deviated from the long-term mean were not the primary drivers of VT identified in the original studies. We conclude that VT anomalies due to annual climate events are only recorded if a combination of favorable conditions coincides.