SOURCE OF ASH-ZONE-1 IN THE NORTH-ATLANTIC

Geochemical evidence shows that the silicic component of the widespread Ash Zone 1 in the North Atlantic is derived from a major ignimbrite-forming eruption which occurred at the Katla caldera in southern Iceland during the transition from glacial to interglacial conditions in Younger Dryas time. Both trace and major element evidence of the rhyolitic products excludes the Or ae fajokull volcano as a source. The high-Ti basaltic component in the marine ash zone can also be attributed to contemporaneous eruption in the Katla volcanic complex. Dispersal of tephra from this event is primarily attributed to the generation of co-ignimbrite ash columns in the atmosphere, with ash fallout on both sea ice and on the ocean floor north and east of Iceland. Owing to the changing ocean circulation characteristics of the glacial regime, including suppression of the Irminger Current and a stronger North Atlantic Current, tephra was rafted on sea ice south into the central North Atlantic and deposited as dispersed Ash Zone 1. Sediments south of Iceland also show evidence of the formation of ash turbidites, generated either by the entrance of pyroclastic flows into the sea, or during discharge of jokulhlaups or glacier bursts from this sub-glacial eruption.