TEPHROCHRONOLOGY AND EARLY HOLOCENE ENVIRONMENTAL CHANGES ON THE FAROE ISLANDS, NORTH ATLANTIC

The Faroe Islands are situated in a uniquely sensitive part of the North Atlantic Ocean for registering Late Quaternary climatic changes. In warmer periods, when generally strong, or northward-displaced, circulation occurs in the atmosphere and ocean, the Faroe Islands lie continually in the main arm of the North Atlantic Drift. In colder periods, when this Drift weakens or its main branch takes a more southerly position, a tongue of polar water from the East Iceland branch of the East Greenland Current approaches the Faroe Islands from the northwest. One of the main aims of this research is to construct a complete Holocene tephrochronology for the Faroe Islands so that the marine record of climate development could be precisely compared with that from the terrestrial data. It also forms an important link between the existing tephrochronological frameworks on the British Isles, Germany and Scandinavia and the volcanic source areas on Iceland. The results from the tephra analyses so far indicate that tephra from the Hekla volcano dominates, with Hekla-4 (c. 4200 cal yr. BP) and Hekla-Selsund (c. 3750 cal yr. BP) as the most prominent horizons. Several basaltic horizons have been recorded in addition to the widespread Saksunarvatn tephra (10,240 cal yr. BP), including the Landnám tephra (c. 870s AD), the Hov tephra (c. 5900 cal yr. BP) and the Mjáuvøtn tephra (c. 6300 cal yr. BP). Three silicic horizons from the Katla volcano are reported for the first time outside Iceland. Two of these are tentatively correlated with the SILK-A1 (c. 5900 cal yr. BP) and SILK-A7 layers (c. 7100 cal yr. BP), respectively. The third tephra is dated to c. 8000 cal yr. BP and has a geochemistry virtually identical to the Vedde Ash (c. 12,000 cal yr. BP) and IA2 tephra from the Rockall Trough (c. 13,500-13,000 cal. yr BP). Palaeoecological analyses record a significant vegetation perturbation between c. 10,380 cal. yr. BP and the deposition of the Saksunarvatn ash suggesting a marked change in climatic conditions. The initially dry continental conditions, which favoured Betula nana, Salix, Juniperus and Ericaceae but not Gramineae or Cyperaceae, were rapidly replaced by a cooler, moister climate. This gave rise to increased erosion and a reduction in lake trophic status. The correspondence between our data and earlier work of Jóhansen (1982) indicates that this is a widespread event.