Chronology and paleoenvironments during the late Weichselian deglaciation of the southwest Iceland shelf ANNE JENNINGS, JAMES SYVITSKI, LINDA GERSON, KARL GRO ¨ NVOLD, A ´ SLAUG GEIRSDO ´ TTIR, JO ´ RUNN HARDARDO ´ TTIR, JOHN ANDREWS AND SVEINUNG HAGEN Jennings, A., Syvitski, J., Gerson, L., Gro ¨nvold, K., Geirsdo ´ttir, A ´ ., Hardardo ´ttir, J., Andrews, J. & Hagen, S. 2000 (September): Chronology and paleoenvironments during the late Weichselian deglaciation of the south- west Iceland shelf. Boreas, Vol. 29, pp. 167–183. Oslo. ISSN 0300-9483. Foraminifera, sedimentology, and tephra geochemistry in core 93030-006 LCF from the southwestern Iceland shelf were used to reconstruct paleoenvironments between 12.7 and 9.4 14 C ka BP. Seismic-reflection profiles place the core in glacial-marine and marine sediments within one meter of the underlying glacial till. Forami- nifers in the earliest glacial-marine sediments provide a record of ice-distal conditions and immigration of slope species onto the shelf in association with warm Atlantic water. Meltwater increased during the Allerød under a weakened Atlantic water influence. Arctic conditions began by 11.14 14 C ka BP with an abrupt in- crease in meltwater and near exclusion of boreal fauna from the shelf. Meltwater diminished in the early Younger Dryas, coinciding with sea-surface cooling between 11.14 and 10.5 14 C ka BP. A slight warming re- corded in the uppermost glacial-marine sediments was interrupted by an inferred jo ¨kulhlaup event emanating from glacier ice on the Western Volcanic Zone. Retreat of the ice margin from the sea sometime between c. 10.3 and 9.94 14 C ka BP coincided with this event. The onset of postglacial marine sedimentation occurred along with increasing evidence of Atlantic water c. 9.94 14 C ka BP and was interrupted by a short-lived Pre- boreal cooling of the Irminger Current c. 9.91 14 C ka BP. Conditions similar to those today were established by 9.7 14 C ka BP. Anne Jennings (e-mail: jenninga@spot.colorado.edu), James Syvitski, Linda Gerson and John Andrews, Cam- pus Box 450, INSTAAR and Department of Geological Sciences, University of Colorado, Boulder, CO 80309- 0450 USA; Karl Gro ¨nvold, Nordic Volcanological Institute, Grensa ´svegur 50, 108 Reykjavı´k, Iceland; A ´ slaug Geirsdo ´ttir, Department of Geosciences, University of Iceland, 101 Reykjavı´k, Iceland; Jo ´ runn Hardardo ´ttir, Science Institute, University of Iceland, Dunhagi 3, 107 Reykjavı´k, Iceland; Sveinung Hagen, Institute of Geol- ogy and Biology, University of Tromsø, 9037 Tromsø, Norway; received 25th May 1999, accepted 9th Febru- ary 2000 Iceland is located in a climatically sensitive geographic position relative to atmospheric circulation and the present-day marine arctic and polar fronts (Fig. 1). Large changes in the positions of the marine polar front mapped for the last deglaciation (Ruddiman & Macin- tyre 1981) have also been observed in the latest Pleistocene to Holocene sediments preserved in Iceland (Rundgren 1995; Ingo ´lfsson et al. 1997). The extent and activity of glaciers in Iceland from the Last Glacial Maximum (LGM) to c. 9 ka were affected by changes in the position of the polar front (e.g. Ingo ´lfsson & Norddahl 1994). The lack of radiocarbon dates on land during the LGM indicates that Iceland was largely ice covered, and that the ice-sheet margins were somewhere offshore. The ice extent during the LGM is often assumed to have been near the shelf-slope break, although there is no firm, dated evidence of this assumption (Denton & Hughes 1981; Ingo ´lfsson & Norddahl 1994; Andrews et al. 2000). Radiocarbon dating of uplifted glacial-marine deposits and lake sediments indicates a stepwise retreat of the ice margins from the contemporaneous periphery of Iceland from c. 12.7 to c. 9.7 14 C ka BP (Ingo ´lfsson & Norddahl 1994 and references therein; Geirsdo ´ttir et al. 1997). Ingo ´lfs- son & Norddahl (1994) suggested that deglaciation began sometime before 13 ka BP in response to climatic amelioration or sea-level rise, but the evidence for the earliest part of the deglaciation must be located offshore. Thus, there is a gap in the information about the glacial history of Iceland between the LGM and 12.7 14 C ka BP, the earliest evidence of the ice margin on land. In addition, there is a lack of continuous, well- dated, high-resolution records of the changes in environmental conditions during deglaciation. The purpose of this article is to present a continuous high-resolution paleoenvironmental record of deglacia- tion of the southwest Iceland shelf between 12.7 and 9.4 14 C ka BP (Fig. 1) based on data collected on cruise HU93030 of the research vessel C.S.S. Hudson. These data include high-resolution seismic reflection profiles tied to sedimentological, tephra, and foraminiferal analyses of radiocarbon-dated core 93030-006 LCF (Long Coring Facility), a giant piston core from Jo ¨kuldjup, Faxaflo ´i Bay (Fig. 1). Physical setting Jo ¨kuldju ´p is a bathymetric depression in outer Faxaflo ´i Bay, southwest Iceland shelf (Fig. 1). The Irminger