High-frequency melting pulses of the Fennoscandian Ice Sheet documented in late Glacial/early Holocene sediments of the Baltic Sea
Gingele F X and M. Moros (Baltic Sea Research Institute, 18119 Warnemuende, Germany)
The retreat and melting of the Fennoscandian Ice Shield in the late Glacial and early Holocene fostered the development of a large meltwater lake, the Baltic Ice Lake. It occupied large areas of the present-day Baltic Sea basin and received considerable amounts of meltwater suspensions from the retreating ice shield. The resulting high sedimentation rates allows the reconstruction of a high-resolution chronology within these sediments. The main problem is the dating of chronological tie points. Three major drainage events at Mt. Billingen in Sweden (B1, B2a, B2b) lowered the lake level considerably. They are dated from several sites in Sweden and Finland at average ages of 11,200, 10,300 and 9,900 years B.P. We present sediment cores from the southwest corner of the Baltic Sea, where these events are documented by distinct sand layers. The sedimentary sequence between sand layers 1 and 2 represents approximately 1000 years and can be divided into 4 cycles with the proxies GRAPE-density, grain size, magnetic susceptibility and dolomite content. Maxima of these proxies correlate and may be interpreted as intensified supply of meltwater suspensions and increase in current dynamics. Since the duration of each cycle (200-300 years) is too short to be driven by internal ice dynamics we assume a response to short-term climate fluctuations. An inrease in temperature would result in an intensification of melting and supply of dolomite-rich suspension from deposits north of the investigation area. The forcing mechanism may be related to centennial fluctuations of the North Atlantic Oscillation Index (NAO). Climatic cycles of similar duration have been sporadically recorded in Southern Ocean sediments implying a common forcing mechanism for both hemispheres.