Anchoring the Swedish Time Scale to the radiocarbon time scale —An absolute age for De Geer’s zero varve Open Access

The Swedish Time Scale (STS), based on annual sediment sequences (varves), is a unique tool for detailing Scandinavian deglaciation and climate history. Over a century in development, the STS comprises ∼13,300 varve-years, yet its connections to calendar years are insecure, and it cannot yet be considered a true absolute time scale. Consequently, it has not been possible to reliably investigate leads and lags of paleoclimate and environmental changes recorded in the STS in relation to other climate archives in NW Europe and the North Atlantic region. Here, we radiocarbon dated a series of early Holocene ice-dammed lake drainage events that deposited recognizable varves downstream. In particular, we identified the lake drainage responsible for depositing the so-called “zero varve” of the STS and dated it to 10,008 ± 87 calibrated years before present, A.D. 1950 (cal. yr B.P.). Using a hydrological model, we demonstrate that drainage duration was subseasonal and that drainage marker beds are, in chronological terms, true annual varves. By doing so, we anchor the STS in absolute time, provide revised ages of key deglacial and climatic events of the last glacial-interglacial transition, and present a tightly chronologically constrained reconstruction of early Holocene ice-sheet retreat in central Scandinavia.