Holocene shore displacement and deglaciation chronology in Norrbotten, Sweden MATTIAS LINDE ´ N, PER MO ¨ LLER, SVANTE BJO ¨ RCK AND PER SANDGREN BOREAS Linde ´n, M., Mo ¨ller, P., Bjo ¨rck, S. & Sandgren, P. 2006 (February): Holocene shore displacement and deglaciation chronology in Norrbotten, Sweden. Boreas , Vol. 35, pp. 1  /22. Oslo. ISSN 0300-9483. The coastal zone of Norrbotten, northern Sweden, was gradually inundated by the Ancylus Lake following the retreating ice margin and forming a highest coastline approximately 210m above the present sea level. The succeeding shore displacement is reconstructed based on lithological investigations and radiocarbon datings of identified isolation sequences from 12 cored lake basins. The highest lake basins, along with two basins above the highest shoreline, suggest ice-free conditions already at 10500 cal. yr BP. This is at least 500 years earlier than previously thought and implies rapid ice-sheet break-up in the Gulf of Bothnia. The shore displacement (RSL) curve represents a forced regression of successively decreasing rate through the Holocene, from 9 m/100 yr to 0.8 m/100 yr. During the first 1000  /1200 years, the isostatic uplift is exponentially declining, followed by a constant uplift rate from c. 9500 cal. yr BP to 5500 /5000 cal. yr BP. The last 5000 years seem to be characterized by a low but constant rebound rate. The development of the Ancylus Lake stage of the Baltic may also be discerned in the Norrbotten RSL curve, suggesting that the chronology of the Ancylus Lake stages may have to be revised. The Littorina transgression is also reflected by the RSL curve shape. In addition, a series of early to mid- Holocene beach terraces were OSL-dated to allow for comparison with the 14 C-dated shore displacement curve. Interpretations of these ages and their relation to former sea levelswere clearly more problematic than the dating of the lake basin isolations. Mattias Linde ´n (e-mail: Mattias.Linden@geol.lu.se), Per Mo ¨ ller, Svante Bjo ¨rck and Per Sandgren, Department of Geology, GeoBiosphere Science Centre, Lund University, So ¨lvegatan 12, SE-22362 Lund, Sweden; received 21st February 2005, accepted 1st July 2005. The eastern part of the province of Norrbotten, northern Sweden, experienced a subaqueous early Holocene deglaciation with water depths up to or slightly exceeding 200 m; fresh water of the Ancylus Lake (e.g. Bjo ¨rck 1995) gradually inundated land areas as the grounded ice-sheet margin receded towards the northwest. The present day 30 /40 km wide coastal plain was totally submerged (Fig. 1C), whereas the more broken landscape further inland  / an inland plain with residual hills 200  /300 m high (cf. Hoppe 1959) / formed a deglacial archipelago. During the continued deglaciation towards the northwest the present valleys of the Pite, Lule and Ra ˚ne Rivers (Fig. 1C) formed deeply incised Ancylus Lake embay- ments at the regional ‘highest shoreline’, above which the deglaciation proceeded in a supra-aquatic setting. Being close to the centre of maximum isostatic recovery for the Scandinavian Ice Sheet, isostatic uplift was faster than the initial water level rise of the transgres- sive Ancylus Lake; the transgression is restricted to the southern Baltic (Bjo ¨ rck 1995). The highest shoreline was thus regressive and metachronous, reaching alti- tudes around 230 m a.s.l. (metres above sea level) in the southeastern part of the investigation area, i.e. closer to the area of maximum thickness of the ice, and declining in a northwestward direction to c. 180 m a.s.l. (Fig. 1C). This reflects the pattern of glacial loading, since the northwestern part of the Bothnian Sea is regarded as the location of maximum ice thickness during the Late Glacial Maximum (LGM) (e.g. Lundqvist 1994). After deglaciation, the isostatic uplift centre gradually moved from A ˚ ngermanland (highest shoreline at 286 m a.s.l.; M. Berglund 2004) to its present location in the western part of the Bothnian Bay (Ekman 1996), with a present uplift rate of 8  /9 mm/yr. The position of the highest shoreline (HS) is distinguished in the landscape by (i) the highest traces of wave erosion on till-covered slopes, (ii) the highest positions of glaciofluvial deltaic deposits (topset beds) and, (iii) the lowest altitudes (the disappearance) of terrestrial proglacial and ice-marginal glaciofluvial erosion channels (Fromm 1965). The most elegant forms associated with the formation of the highest shoreline are the till-capped hills (in Swedish: kalott- berg; Fig. 2E). These were islands in the deglacial archipelago, indicated by preserved till above the highest shoreline, often with wave-washed bare bed- rock below facing the predominating storm direction from south and southeast and with deposition of beach sediments/ridges at falling altitudes on the leeward side (cf. Hoppe 1959; Fromm 1965). The large-scale geomorphology is characterized by southeast  /northwest trending broad valleys and bedrock hills. Streamlined bedrock knobs, drumlins and leeside moraines, all preferentially on higher DOI 10.1080/03009480500359160 # 2006 Taylor & Francis