The Dimna Ash — a 12.8 14C ka-old volcanic ash in Western Norway

Abstract

A new volcanic ash, named the Dimna Ash, geochemically similar to the rhyolitic component of the Vedde Ash, is described in a core from a palaeo-lake in Western Norway. The Dimna Ash occurs more than a metre below the Vedde Ash and radiocarbon datings indicate a minimum age of 15,100 calendar years BP (12,800 14C years BP). In comparison the age of the Vedde Ash is 12,120 calendar (NGRIP) years BP (10,300 14C years BP). The Dimna Ash is invisible to the naked eye in the core and was detected by applying a density separation technique. It comprises, however, up to 12,900 ash shards per cm 3 sediment. We conclude that the Dimna Ash is wind-blown from Iceland and should therefore be found also in marine cores between Iceland and Norway and thus has the potential to become an important marker horizon. The core also contains scattered ash shards, geochemically similar to the Borrobol Ash, that are spread over a 50 cm thick zone deposited between 13,400 and 12,700 calendar years BP. This is the first discovery of Borrobol-like ash in Norway.