Proposing a new conceptual model for the reconstruction of ice dynamics in the SW sector of the Scandinavian Ice Sheet (SIS) based on the reinterpretation of published data and new evidence from optically stimulated luminescence (OSL) dating

Abstract

Abstract. We propose a new concept of the Weichselian ice dynamics in the south-western sector of the Baltic Sea depression. The review of existing geochronological data from Germany, Denmark and southernmost Sweden in combination with new optically stimulated luminescence (OSL) data from the German Oder Lobe area is the basis for a reassessment and an improvement of previous ice dynamic models. Factors like the pre-existing topography, glaciotectonic features and the occurrence of till beds and inter-till deposits of varying origin are also taken into consideration for our process-based reconstruction of the sedimentary environments close to the ice margin and hence the ice dynamics of the Scandinavian Ice Sheet (SIS). During the early MIS 3 (marine isotope stage), the late MIS 3 and MIS 2, the SIS advanced into present-day terrestrial areas around the south-western Baltic Sea Basin. The first ice advance during the warming phase in early MIS 3 is poorly documented as the Ellund–Warnow Advance in Germany but may be correlated with the numerically dated Ristinge Advance in Denmark and Sweden. The late MIS 3 advance in contrast is reliably documented. It shaped the landforms of the Brandenburg Advance and the maximum Weichselian ice extent in the Oder Lobe area in north-eastern Germany and occurred contemporaneously with the Klintholm Advance in southern Sweden and Denmark. The lack of a corresponding till in various cliff profiles along the Baltic Sea coastline between southern Schleswig-Holstein and the island of Rügen can be explained by the distinct lobate structure of this ice advance, which was strongly guided by the pre-existing low-lying topography. We propose the horst of Bornholm, Denmark, acting as an ice divide, with ice-dammed lakes existing on the lee side between two glacier lobes. This lobate structure had not been considered in previous conceptual models, which led to seemingly conflicting chronological and stratigraphical interpretations. Our introduction of the lobate structure for the first time resolves these contradictions and integrates the data in a coherent model. The dynamics of the MIS 2 readvance to the Last Glacial Maximum (LGM) extent were clearly different to the previous advance and were most likely characterized by a more uniformly advancing ice front with a less lobate structure which also overrode the horst of Bornholm and the island of Rügen. This advance reached the maximum Weichselian ice extent in some parts of the south-western SIS, but, in the Oder Lobe area, it is proven to have terminated at a lesser extent than the early MIS 3 advance, but it did shape the most prominent morphological landform record of the last glacial cycle. In order to advance the reconstruction of Weichselian ice dynamics in the future, we strongly suggest using both an MIS-based terminology and a process-based approach in the interpretation of geochronological data to live up to the dynamic nature of continental ice sheets.

Surface cracks—geomorphological indicators for late Quaternary halotectonic movements in Northern Germany

“…During the Weichselian, at least two ice advances reached Northern Germany, with the older advance (W1, late MIS 3 to early MIS 2, c. 30 ka) reaching farther south than the younger (W2, MIS 2, c. 20 ka). Thus, the Weichselian glacial landscapes can be differentiated in an older (W1 advance) and a younger (W2 advance) young morainic area (Hardt et al, 2016;Lüthgens et al, 2011Lüthgens et al, , 2020.…”

“…Central and parts of southern Brandenburg were last glaciated during the late MIS 3/early MIS 2 (W1 advance) and were ice-free after 30 to 25 ka onwards (Hardt et al, 2016;Lüthgens et al, 2020). Only Northern Brandenburg and regions to the north were glaciated again during the MIS 2 (W2 advance) and ice-free from c. 19-18 ka onwards (Lüthgens et al, 2011(Lüthgens et al, , 2020.…”

“…The cracks must have formed after the respective areas were last glaciated by the Weichselian ice sheet because any pre-existing cracks must have been deformed by the advancing ice or filled with sediment in the glacial or paraglacial depositional environments. Central and parts of southern Brandenburg were last glaciated during the late MIS 3/early MIS 2 (W1 advance) and were ice-free after 30 to 25 ka onwards (Hardt et al, 2016;Lüthgens et al, 2020). Only Northern Brandenburg and regions to the north were glaciated again during the MIS 2 (W2 advance) and ice-free from c. 19-18 ka onwards (Lüthgens et al, 2011(Lüthgens et al, , 2020.…”

“…Large parts of Northern Germany and the adjoining areas were shaped by the advances of the Scandinavian Ice Sheet (SIS) during the Pleistocene (Böse et al, 2012). Throughout the last decade, significant progress has been achieved in the understanding of the timing and dynamics of the ice advances (Hughes et al, 2016;Lauer & Weiss, 2018;Lüthgens et al, 2020;Roskosch et al, 2015;Stroeven et al, 2016), as well as in deciphering the related surface processes.…”

“…Large parts of Northern Germany and the adjoining areas were shaped by the advances of the Scandinavian Ice Sheet (SIS) during the Pleistocene (Böse et al, 2012). Throughout the last decade, significant progress has been achieved in the understanding of the timing and dynamics of the ice advances (Hughes et al, 2016; Lauer & Weiss, 2018; Lüthgens et al, 2020; Roskosch et al, 2015; Stroeven et al, 2016), as well as in deciphering the related surface processes. For the latter, the growing availability of high‐resolution digital terrain models is of substantial importance, as these models allow precise mapping of landforms, leading to new insights in ice‐related geomorphic processes, such as drumlin formation (Clark et al, 2009), erosion by subglacial meltwater (Lesemann et al, 2010), formation of ice‐marginal fans (Hardt et al, 2015) and ice‐stream patterns (Szuman et al, 2021), as well as glacitectonic deformations (Gehrmann & Harding, 2018).…”