Norwegian Sea tephrostratigraphy of marine isotope stages 4 and 5: Prospects and problems for tephrochronology in the North Atlantic region

This paper presents an account of the tephrostratigraphy of south eastern Norwegian Sea core MD99-2289 for the interval spanning Marine Isotope Stage (MIS) 5 and part of MIS-4 (from ∼70 000 to 130 000 years ago). Tephra deposits from in the order of 100, mainly basaltic, volcanic eruptions in Iceland and on Jan Mayen are described in terms of their stratigraphic context and geochemical composition, representing the most comprehensive record of Iceland and Jan Mayen volcanism over this time span. The most important transport mechanism of tephra to the core site is considered to have been iceberg rafting which is thought to be responsible for a centennial to millennial scale time lag between the volcanic eruption events and the subsequent deposition of tephra in deep-sea sediments. While this clearly limits the use of some of the tephras as isochronous markers, twelve discrete tephra deposits show stratigraphical and geochemical characteristics that suggest them to have been deposited near – contemporaneously with their source volcanic events, and hence suitable candidates as regional isochrones. Four of these accords with the geochemical signatures of tephra deposits previously described from the Nordic Seas region. Potential problems for the application of tephrochronology highlighted by this work are discussed and recommendations for strategies to overcome them are proposed.