High-resolution paleomagnetic dating of sediments deposited in the central Baltic Sea during the last 3000 years A.T. Kotilainen * , T. Saarinen, B. Winterhalter Geological Survey of Finland, Betonimiehenkuja 4, SF-02150 Espoo, Finland Received 23 June 1999; accepted 21 January 2000 Abstract Sediment cores from the main sedimentary basin in the Baltic Sea, the Gotland Deep, provide a high-resolution record of changes in the Holocene paleo-environment and paleoclimate. Due to the inherent inaccuracy (reservoir effect, redeposited material) of the 14 C dating method in dating marine sediments, the known changes in the Earth’s magnetic field recorded in three sediment cores from the Gotland Deep were used to produce a more detailed and accurate timescale. The variations in the inclination and declination were compared to the paleosecular variations over the last 3000 years recorded in annually laminated lake sediments from Finland. This correlation made it possible to construct, for the late Holocene Gotland Deep sediments, a high-resolution time-scale with an estimated absolute accuracy of better than ^50 years. This new timescale made it possible to determine the mean annual rates of sedimentation with an unprecedented accuracy. The sedimentation rates were found to have varied considerably both in time (from 0.2 up to 4.3 mm/year) and space, indicative of the patchy nature of accumulation in the Gotland Deep during the past 3000 years.  2000 Elsevier Science B.V. All rights reserved. Keywords: Baltic Sea; Sediments; Paleomagnetism; C-14 dating; Magnetic susceptibility; Holocene 1. Introduction The Earth’s magnetic field is in a state of constant change and its direction and strength vary continu- ously on timescales ranging from milliseconds to millions of years. Long-term variation with periods ranging from a few years to 10 4 years is called secular variation of the geomagnetic field (Merrill et al., 1996). These secular variations are recorded in the form of a continuous time series in sediments (Mack- ereth, 1971). Minute mineral grains with magnetic properties settling on the bottom are oriented parallel to the Earth’s magnetic field existing during the time of deposition (e.g. Barton et al., 1980; Shcherbakov and Shcherbakova, 1983; Tucker, 1983; Shive, 1985). This magnetic orientation may remain unchanged when these magnetic sediment particles become buried by subsequent sedimentation and can be measured from the sediment core. Holocene paleomagnetic studies in Fenno-Scandi- navia have been mainly focussed on lake sediments (e.g. Tolonen et al., 1975; Stober and Thompson, 1977, 1979; Huttunen and Stober, 1980; Saarinen, 1994, 1998). Most recently Saarinen (1999) has used paleomagnetic secular variations to date some lake sediment sequences from Finland and Russia covering the last 3200 years. It should be noted that so far only very few paleomagnetic studies have been made on Baltic Sea sediments (e.g. Rother, 1989; Abrahamsen, 1995). The 14 C method has been used extensively for Marine Geology 166 (2000) 51–64 0025-3227/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0025-3227(00)00012-8 www.elsevier.nl/locate/margo * Corresponding author. Fax: + 358-2055012. E-mail address: aarno.kotilainen@gsf.fi (A.T. Kotilainen).