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. 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.


Introduction
This supplementary document provides complementary details to the basic information provided in the main text about the luminescence dating approach applied, and about the sedimentological and stratigraphic context for the two new sites investigated in this study.All laboratory analyses described here were conducted at the Vienna Laboratory for Luminescence dating (VLL).This included mechanical and chemical sample preparation steps, high-resolution gamma spectrometry measurements, all luminescence analyses, and final age calculation.For all stratigraphic and geomorphological implications please see the text in the main paper.

Sample preparation
The luminescence samples were delivered to the VLL in closed, light-tight plastic cylinders.All subsequent sample preparation steps were conducted under subdued red-light conditions according to the procedures described by e.g.Hardt et al. (2016) and Lüthgens et al. (2017).Samples were opened and the outer few centimetres of material exposed to daylight during sampling were carefully removed.Only the inner parts of the cores were used for all subsequent preparation steps.Separates of pure quartz (in the grain size fraction of 170 -250 µm for Jänschwalde and 220 -250 µm for Müncheberg) were extracted by a procedure including drying of the sediment at 50°C, dry sieving, leaching of carbonates (10% HCl) and organics (10% H2O2), dispersion of aggregates and clay coatings (Na2C2O4, 0.01 N), and density separation (LST Fastfloat at 2,68 g/cm 3 ).
Samples for radionuclide analyses were taken from the direct surroundings of the luminescence samples and were first dried, manually homogenized (gentle crushing of aggregates) and subsequently sealed in Marinelli beakers (500ml equivalent to ~1kg dry weight of sample material) and stored for at least a month before measurement to establish secondary secular Radon (Rn) equilibrium.

Determination of the equivalent dose
Quartz was used as a dosimeter for all measurements, because the luminescence signal of quartz is known to be reset by daylight exposure much faster than that of feldspar.In glaciofluvial sediments, incomplete bleaching (incomplete resetting of the luminescence signal prior to burial) is known to occur frequently (e.g.Lüthgens et al. 2010a/b, 2011, Hardt et al. 2016) and leads to age overestimation if not detected and corrected for.We measured quartz grains in the grain size fraction of 170 -250 µm (Jänschwalde) and 220 -250 µm (Müncheberg).The aliquot size was 1 mm for the Jänschwalde samples, and 2 mm for the Müncheberg samples, which results in an average of 15 -25 grains per disc.In previous tests on Weichselian glaciofluvial material on single grains we observed that only 3 -5 % of the quartz grains emit a significant luminescence signal (Lüthgens et al., 2010b;Hardt et al., 2016).Thus, the measurements were done on a quasi-single grain level, which is an important prerequisite when working on poorly bleached (glaciofluvial) material.All measurements were carried out at the VLL on Risø DA-20 automated luminescence reader systems (Bøtter-Jensen et al. 2000, 2003).The quartz emission from multigrain aliquots was stimulated using blue (470 nm) light emitting diodes (LEDs) and detected through a 7.5-mm Hoya U340 filter by a photomultiplier.For necessary irradiation steps all reader systems are equipped with a 90 Sr/ 90 Y beta source delivering a dose rate of approximately 0.1 Gy/s.The suitability of the applied single aliquot regenerative dose (SAR) protocol (Murray & Wintle 2000& 2003, Wintle & Murray 2006) using a preheat of 10 s @ 240 °C and a cutheat for another 10 s @ 220 °C was confirmed by dose recovery experiments on selected samples which yielded recovery ratios (measured/given dose) within 10 % of unity.Some authors recommend early background subtraction (EBG) to ensure the isolation of the fast component of the quartz OSL signal (Ballarini et al., 2007, Cunningham andWallinga, 2010).Quartz from the study area is known to be fast component dominated (Lüthgens et al. 2010a, 2010b, 2011, Hardt et al. 2016), but we still compared dose distributions using EBG vs. late background subtraction (LBG) for both, dose recovery experiments and natural equivalent dose measurements.In all cases, LBG yielded results in agreement with the EBG-approach, but with a significantly higher yield of equivalent dose values than obtained for the EBG-approach.Therefore, the first 0.9 s of stimulation were used for signal integration, whereas the last 10 s served as background.Aliquots were accepted when fulfilling the following rejection criteria: recycling ratio <15% and maximum recuperated dose < 5% of the natural signal (both including uncertainty).A representative dose response curve and a decay curve are provided in figure S1.

Determination of the dose rate
Activities of occurring radionuclides ( 238 U and 232 Th decay chains, as well as 40 K) within the sediment were determined by highresolution, low-level gamma spectrometry.To achieve a preferable signal to noise ratio, each sample was measured for 24 hours at the VLL using a Canberra HPGe (40 % n-type) detector.The external dose rate was calculate based on the results from radionuclide analysis (table S1), using the conversion factors of Adamiec & Aitken (1998) and the β-attenuation factors of Mejdahl (1979).An average water content 8 ±4 % was estimated for the time of burial, because of the good drainage within the sandy deposits and no water-impermeable layers close below the sampling spots.The uncertainty assigned to the water content was propagated to the final dose rate and age calculation.
Table S1: Summary of results from OSL dating 1 Activities determined by low-level gamma spectrometry (Canberra n-type detector, ~40 % efficiency) at the VLL. 2 Overall environmental dose rates based on the provided radionuclide activities and calculated using 8±4% water content and using conversion factors of Adamiec & Aitken (1998) and β-attenuation factors of Mejdahl (1979); cosmic dose rate determined according to Prescott & Stephan (1982) and Prescott & Hutton (1994). 3De calculated using the three parameter minimum age model (MAM) according to Galbraith et al., (1999) using the R Luminescence package (Kreutzer et al., 2012) and a threshold of 0.2 for the sigma_b parameter. 4Calculated using the software ADELE (Kulig, 2005).Ages in bold used for the calculation of the average ages.The cosmic dose rate was determined according to Prescott & Stephan (1982) and Prescott & Hutton (1994), taking into account the geographical position of the sampling spot (longitude, latitude, and altitude), the depth below surface, as well as the average density of the sediment overburden.An uncertainty of 10% was assigned to the calculated cosmic dose rate.The resulting overall dose rate is provided in table S1.

Results
The majority of samples showed good performance with regard to the quality criteria of the SAR protocol and yielded sufficient numbers of equivalent dose values for further data evaluation.A representative dose distribution is shown in figure S2.All these samples show clearly right-skewed dose distributions and overdispersion values typically ranging from >30 % to >50 %.Both factors in combination are strong indicators for significant incomplete bleaching present in the samples.Consequently, the three parameter minimum age model of Galbraith et al. (1999) was applied to calculate paleodose values for the samples.The threshold for the minimum expected overdispersion was set to 20 % as based on the overdispersion parameters observed from few well bleached samples from the broader research area in earlier studies (Lüthgens et al. 2011, Hardt et al. 2016).For two samples (JAE-II-13 & WIL-III-1) the yield of obtained equivalent dose values was very low.This was caused by a high number of aliquots showing natural doses above the highest laboratory dose administered in the SAR protocol, which can be interpreted to have been caused by extremely poor incomplete bleaching.While sample JAE-II-13 showed at least few individual equivalent dose values in line with the equivalent doses from the overand underlying samples, sample WIL-III-1 did not show any dose values even close to those expected.
Tests using significantly higher maximum laboratory doses confirmed that trend and even showed large numbers of aliquots with oversaturation effects (natural dose not  intersecting with the saturated laboratory dose response curve).Only maximum ages could be calculated for samples JAE-II-13 & WIL-III-1, and they were excluded from all further evaluation.All age and dose rate calculation was done using the software ADELE (Kulig 2005).

Reliability of the data
The ages determined for all samples of each site are in good agreement within error, which reliably demonstrates that effects of incomplete signal resetting were successfully identified and corrected for by the applied SAR protocol and the subsequent statistical data evaluation approach.Average ages were calculated for each site (See supplementary table 1), which are in excellent agreement within error and line up perfectly with results from sites ascribed to the same ice advance in the research area as described in detail in the main manuscript.

Ages in stratigraphic context
All stratigraphic and geomorphological implications of the new ages are described in the text of the main paper.Sedimentological details are summarized in figures S3 and S4.

Figure S1 :
Figure S1: Representative dose response curve (sensitivity corrected luminescence signal (Lx/Tx) plotted vs. dose (Gy)) and decay curve for an aliquot of sample JAE-II-11.Plots generated using the R-luminescence package of Kreutzer et al. (2012).

Figure S2 :
Figure S2: Representative equivalent dose distribution and basic statistical parameters for sample JAE-II-11.Please note that the distribution is rightskewed and shows an overdispersion of >50%, which indicates that the sample was not fully bleached before deposition.Plot generated using the Rluminescence package of Kreutzer et al. (2012).

Figure S3 :
Figure S3: Stratigraphic log for the sampling site Jänschwalde and OSL ages in stratigraphic context.Genetic interpretation codes: p -periglacial; fgglaciofluvial; l -limnetic. 1Age excluded from mean age calculation.
Supplementary information to "Proposing a new conceptual model for the reconstruction of ice dynamics in the SW sector of the Scandinavian Ice Sheet (SIS)"