Comment on gchron-2022-26

Abstract

The Vedde Ash, first described in Norway and dated to ~12000 cal a BP, has been taken to represent tephra derived from a large eruption of the Katla volcano in Iceland and dispersed across the North Atlantic and Europe. However, evidence for tephra layers with similar composition to the Vedde Ash, but of different ages, questions the utility of isolated Vedde-like tephra layers as reliable and independent age control. Here, we report three stratigraphically separated Early Holocene Katla tephra layers from the lake Torfdalsvatn, in north Iceland, that have bimodal chemical composition similar to the Vedde Ash. By using previously published conventional 14C ages and revised calibration curves, we provide new ages for these tephra layers of ~11375, 11360, and 11200 cal a BP – all substantially younger than the Vedde Ash. Torfdalsvatn’s record stands as an important reminder that repeated explosive eruptions of Iceland’s major volcanos during the deglacial cycle have produced multiple tephra plumes with similar geochemistry that may span 1000s of years. As a result, we urge caution when using isolated Icelandic tephra layers in distant regions as precise geochronometers without supporting age control.