The afforested dunes at southern Krakower See (Fig. 3, 53^∘35^′32^′′ N, 12^∘15^′59^′′ E) are of irregular shape and cover glacifluvial sands and gravels of the Pomeranian Phase. Their poorly developed or eroded top soils (predominantly podzolic Arenosols) include considerable amounts of incorporated charcoal, which points to a land-use history with deforestation resulting in a strong impact on the upper soil horizons (e.g. charcoal kilns). In addition to soils of late Holocene origin, a buried late glacial surface indicated by a Bwb horizon (brunic Arenosol) was revealed by pedological mapping (Lorenz, 2007; Kaiser et al., 2007). Based on its stratigraphic and pedological features, the brunic Arenosol has been classified as so-called Finow soil following Schlaak (1998, in German Finowboden). The Finow soil has been found and described by several authors in the northern parts of Germany and Poland and dates into the Allerød to Preboreal (e.g. Bussemer et al., 1998; Bogen et al., 2003; Kaiser et al., 2009; Küster and Preusser, 2010). Very close to a fossil cliff at the southern shore of Krakower See, a 10–20 cm thick Bwb horizon is preserved at depths between 60 and 120 cm. It represents a buried terrestrial surface without groundwater influence declining to the south. Thus, the buried surface at this location reveals a gradient orientated opposite to the present surface. A radiocarbon-dated charcoal particle from the Bwb horizon in profile P1 (Fig. 3) suggests the Late Glacial age of the palaeosol (12.9 ka calBP Kaiser et al., 2007), but further investigations with a portable optically stimulated luminescence (OSL) reader (pOSL Sanderson and Murphy, 2010) and common OSL datings have recently been carried out to gain an additional chronology for the formation of the overlying dunes (Fig. 4 Kaphengst, 2015).

The pOSL reader used for this study operates in continuous-wave stimulation mode with 880 nm for infrared stimulated luminescence (IRSL) and 470 nm for optical stimulated luminescence (OSL), where integrated IRSL and OSL signal intensities, depletion rates, and the IRSL ∕ OSL ratio are measured. IRSL and OSL signal intensities respond to a combination of the post-depositional age of the sediment, the luminescence sensitivity of the tested mineral grains, the local dose rates, the completeness of bleaching and potentially inherited luminescence signals due to prior cycles of environmental irradiation (Sanderson and Murphy, 2010). A total of 20 samples have been measured without any chemical pretreatment. Based on the luminescence data (photon counts from the portable reader) profile P1 has five luminescence zones (LZs, Fig. 4). LZ1 relates to the lowermost part of the profile with laminated glacifluvial sediments. LZ2 comprises six samples, where the first and the last one indicate a mixed signal. The samples in between show similar photon counts, pointing to a rapid sedimentation of LZ1 and LZ2. Lamination and the cross-bedding in both luminescence zones give evidence for glacifluvial environments associated with the Pomeranian Phase. LZ3 represents the Bwb horizon of the brunic Arenosol from which two measurements were obtained. For this horizon clay, silt, organic content (LOI) and the chemical index of alteration (CIA Nesbitt and Young, 1982) have the highest values. The CIA is used as a geochemical indicator for the weathering of feldspar and the associated formation of clay minerals, which helps to detect palaeosol formation, e.g. in homogeneous sediment successions (p. 10 Sheldon and Tabor, 2009). LZ4 comprising predominantly unstratified fine sand with low organic content continues with nearly the same photon counts as in LZ3 and shows decreasing pH and CIA values. LZ4 is of aeolian origin. LZ5 represents the present A horizon in fine sand with a distinct podzolic influence and linearly decreasing photon counts from 25 cm upwards, which indicates a stratigraphic break probably related to hiatus. This section is characterised by a minimum pH value of 3.6. However, the pOSL results illustrate nonuniform phases of sedimentation with the leaping photon counts.

The Bwb horizon of the brunic Arenosol lies in between laminated and cross-bedded glacifluvial deposits in the lower part and unstratified aeolian sediments in the upper part of profile P1. With similar stratigraphic position and lithology Küster and Preusser (2010) characterised the Bwb horizon for another site in southern Mecklenburg as a cover sand (GDS, Geschiebedecksand). The luminescence profiles show that the GDS has nearly the same photon counts as the overlying material. This indicates mixing of the material from the GDS and the aeolian coversands. The Finow soil shares properties with the cover sands (Geschiebedecksand), including poor sorting and a high content of finely grained aeolian sediment (Schlaak, 1998). Its depositional environment is assumed to have been influenced by weathering, but not by permafrost (p. 53 Bussemer et al., 1998). The preliminary OSL dates from profile P1 (Fig. 4) point to a Weichselian spectrum with Last Glacial Maximum ages for the well-stratified glacifluvial sediments and a Late Glacial age for the aeolian sands on top of the Finow soil. All three dates support the models of Finow soil formation mentioned above during the period from the Allerød to Preboreal.

The western fringe of the dune field comprises late Holocene dunes, which developed into the aggradational fringe of Krakower Obersee (Fig. 3, P2). Profile P2 shows a gleyic dystric Histosol covered by ca. 100 cm of aeolian sands. A remarkable feature in the profile is that organic soil horizons start 1 m above the present lake level. The dark and strongly organic fossil soil represents the lake level before the artificial lowering in 1836 by 1.05 m, which led to the formation of the 1 m lake terrace (Fig. 3 Lorenz, 2003). It is concluded that the dune field was built up by late glacial aeolian dynamics, as well as by the impact of historical land use. Both profiles indicate a constant reworking of the topsoils and late glacial aeolian sands.

Laboratory data are available from the authors.

SL, HR, MK and SK participated in the fieldwork. SK performed the laboratory analyses and luminescence measurements. MK and HR conducted the luminescence datings. SL wrote the paper and prepared all figures. HR, MK and SK contributed to the paper.

The authors declare that they have no conflict of interest.

This research has been supported by the DFG (German Research Foundation, grant no. 393148499) and the Open Access Publication Fund of the University of Greifswald.