OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Timothy F. Johnsen1,3, Lars Olsen2 and Andrew Murray3 1Corresponding author. Department of Physical Geography and Quaternary Geology, Stockholm University, 106 91 Sweden, [email protected] 2NGU, Geological Survey of Norway, N-7491 Trondheim, Norway, [email protected] 3Nordic Laboratory for Luminescence Dating, Aarhus University, Risø National Laboratory, Frederiksborgvej 399, Build. 201, P.O. 49, DK-4000 Roskilde, Denmark Submitted to Quaternary Science Reviews, February, 2010 © Timothy F. Johnsen, ISBN: 978-91-7447-068-0, ISSN: 1653-7211

Abstract Recent work has suggested that the Scandinavian ice sheet was much more dynamic than previously be- lieved, and its western marine-based margin can provide an analogue to the rapid-paced fluctuations and deglaciation observed at the margins of the Antarctic and Greenland ice sheets. In this study we used a complimentary dating technique, OSL (Optically Stimulated Luminescence dat- ing), to confirm the existence of the Trofors interstadial in central Norway; an ice-free period that existed from ~25 to 20 ka recorded at multiple sites throughout Norway (cf. Andøya interstadial) and that divides the Last Glacial Maximum (LGM) into two stadials. OSL signal component analysis was used to optimize data analysis, and internal (methodological) tests show the results to be of good quality. Both large and small aliquots gave consistent OSL ages (22.3 ±1.7 ka, n = 7) for sub-till glaciofluvial/fluvial sediments at the Langsmoen stratigraphic site, and an apparent old age (~100 ka) for a poorly bleached sample of glacio- lacustrine sediment at the nearby stratigraphically-related Flora site. Eight radiocarbon ages of sediment from the Flora site gave consistent ages (20.9 ±1.6 cal. ka BP) that overlap within 1 with OSL ages from the nearby Langsmoen site. The similarity in age within and between these stratigraphically-related sites and using different geo- chronological techniques strongly suggests that this area was ice-free around ~21 or 22 ka. The existence of the Trofors interstadial along with other interstadials during the Middle and Late Weichselian (MIS 3 and MIS 2) indicates that not only the western margin, but the whole western part of the Scandinavian ice sheet, from the ice divide to the ice margin was very dynamic. These large changes in the ice margin and accom- panying drawdown of the ice surface would have affected the eastern part of the ice sheet as well.

Keywords: Optically stimulated luminescence (OSL) dating, Scandinavian ice sheet, Trofors interstadial, MIS 2, LGM, Norway

Introduction 1981, 2003, 2010, Larsen et al. 1987), Hattfjelldal interstadial I (~39 to 34 ka, cf. Ålesund and Sandes Stratigraphic and chronologic study of sub-till interstadials at the western coast, Andersen et al. sediments from many sites throughout Norway has 1981, Mangerud et al. 1981, 2003, 2009), revealed that the Scandinavian ice sheet behaved in Hattfjelldal interstadial II (~32 to 29 ka, cf. two a much more dynamic manner than previously dates of bones representing the Hamnsund intersta- believed (Olsen 1997, Olsen et al. 2001a,b,c, dial at the western coast, Valen et al. 1996), and 2002). Four interstadials during the Middle and Trofors interstadial (~25 to 20 ka, cf. Andøya in- Late Weichselian glaciation mark periods of major terstadial at the northwestern coast, Vorren et al. ice retreat, and sub-till sediments from these peri- 1988) with intervening stadials bracketing the Tro- ods have been identified and dated at many sites fors interstadial termed LGM 1 and LGM 2 (Last throughout Norway, indicating near-synchronous Glacial Maximum; Fig. 2). The work by Olsen and behaviour of the western margin of the ice sheet colleagues represents a significant leap forward in (Figs. 1 and 2). These interstadials are the Middle our knowledge, and has important implications for Weichselian pre-Hattfjelldal interstadial (~55 to 45 our understanding of ice sheet dynamics and pa- ka, cf. Bø and Austnes interstadials at the western leoglaciology, vegetation dynamics, and the rela- coast, Andersen et al. 1981, 1983, Mangerud et al. tionships between climate change, sea level

1 Timothy F. Johnsen, Lars Olsen and Andrew Murray

Fig. 1: Overview map with locations of the Hattfjelldal I, Hattfjelldal II and Trofors interstadials and their correlatives in different parts of Norway. Langsmoen “L” and Flora “F” stratigraphic sites indicated. Locations of other sites from Finland and Sweden, also mentioned in the paper are also indicated, and several of the sites where bones of mammoth “M” have been found and dated to Middle and early Late Weichselian age are also included (see the main text for references). Curved large and small arrows are for- mer ice streams, solid line is the LGM ice margin, and the dashed line is the Younger Dryas ice margin (compiled from various sources by Olsen et al. 2001a). Ruunaa is just off the east edge of map at N 63°26’ latitude. In cases where two or more of the Tro- fors interstadial sites are located within a few hundred metres to a few kms one dot in the map may represent more than one site. Thus, the sum of dots and triangles with dots is less than the actual number of Trofors interstadial sites (42).

2 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

dating Quaternary sediments (Murray and Olley 2000, Murray and Wintle 2000, Duller 2004, Lian and Roberts 2006, Wintle 2008). Thus, to improve our understanding of the ice dynamics for the western portion of the Scandinavian ice sheet we have used the OSL dating technique to date sub-till sediments from central Norway as an independent dating control for comparison to radiocarbon dated sediments.

A dynamic ice sheet Fig. 2: Frequency distribution of uncalibrated radiocarbon dates (running mean ages ±l) of organic-bearing sediments The dynamics of the Scandinavian ice sheet have and shells from four ice-free intervals separated by glacial been explored by a number of workers (e.g., Sejrup episodes during the Middle to Late Weichselian. The sug- et al. 1994, 2000, 2009, Arnold et al. 2002, Hou- gested names, the number of dates (N) and their mean age (n in 14C ka) for each ice-free interval are indicated. The differ- mark-Nielsen and Kjær 2003, Mangerud et al. ence in mean ages between these groups of dates is significant 2004), and the work by Olsen and collaborators at a 99% confidence level (based on data presented in Olsen et (Olsen 1997, Olsen et al. 2001a,b,c, 2002) is par- al. 2001b). See text for corresponding calibrated ages. Figure from Olsen et al. 2002. ticularly relevant to this study. Based upon the regional Quaternary stratigraphy, using data from more than 50 sections from own studies and sev- change, physiography, and Earth rheology. Knowl- eral others, more than 300 dates (of which ~120 edge of very dynamic ice-margins in the past is were radiocarbon dates taken from own projects), especially pertinent given recent observations of fossil content and some paleomagnetic data, glacia- ongoing rapid but episodic glacier acceleration and tion curves have been constructed for nine tran- thinning from marine-terminating sectors of the sects from inland to shelf covering the latitudinal Greenland and West Antarctica ice sheets (Shep- range of Norway (1800 km; Fig. 1). Comparison of herd and Wingham 2007) and their possible im- these curves, including statistical analysis of the pacts on our environment. The landforms and datings, indicates that the Middle to Late Weich- sediments of the former Scandinavian ice sheet are selian glaciation in Norway was punctuated by four accessible for study, and its western marine-based major ice recessions (Fig. 2; details presented margin can provide an analogue to the rapid-paced above). These interstadials correlate well with fluctuations and deglaciation observed at the mar- peaks in the ice-rafted debris record. This recon- gins of contemporary polar ice sheets. struction of ice oscillations is based mainly (~60%) Despite the importance of the work by Olsen on AMS radiocarbon dates of glacial sediments and colleagues it has not been fully embraced by with low organic carbon content (0.2-1.5%), which the scientific community because it depends mostly gave promising results with respect to accuracy (~60%) on results from AMS radiocarbon dating of and precision (Olsen et al. 2001c). As the age esti- glacial sediments with low organic carbon content, mate of the oldest of these interstadials is close to a method which has some inherent uncertainties the age-limit of the radiocarbon technique, we will (Olsen et al. 2001c) and consequently has been met for the remaining part of this paper only deal with by some scepticism (e.g., Mangerud 2004). An- the three younger interstadials. The rapid and other reason is that results from this work represent rhythmic ice fluctuations, as reconstructed in this a significant departure from earlier views of a more model, have been fairly synchronous in most parts stable ice sheet particularly during the Late Weich- of Norway. Given the regional synchroneity and selian (Denton and Hughes 1981, Mangerud 1991, rapidity of glacial fluctuations it is suggested that 2004, Donner 1995, Ehlers 1996). Given the impli- in addition to precipitation, the mountainous fjord cations and controversy of this work it is important and valley topography, glacial isostasy and relative to assess it further, and the optically stimulated sea level changes were probably more important luminescence (OSL) dating technique has devel- for the size of the glacial fluctuations than were air oped to a point that it can be confidently applied in

3 Timothy F. Johnsen, Lars Olsen and Andrew Murray

temperature changes (Olsen et al. 2001a; cf. Ar- and in the inland areas. The ice advances along the nold et al 2002, Hubbard et al. 2009). main fjords were supported by ice flowing from Does the dynamic ice model described by Olsen most tributary valleys and fjords. Consequently, in et al. (2001a) allow for realistic ice retreat and this model, the average rate of advance for the ice advance rates? Ice retreats of 200-400 m per year sheet moving from inland to coast may have been and ice advances of the same rate would be much very rapid, possibly up to 200-400 m per year more than needed to fit with the age model for the along fjords, although each contributing glacier described Middle to Late Weichselian glacier fluc- may have advanced at much slower rates, less than tuations. If Norway topographically had a tabular 200 m per year. The west-east distance between the form with no deep fjords and valleys and no high outer coastline and the Langsmoen and Flora sites mountains, then such rates for ice retreats and ad- is ~110-113 km, and with an ice retreat rate as high vances would seem to be extremely high and quite as 200-400 m per year the ice margin could have unrealistic. However, Norway is highly dissected retreated from the coast to Langsmoen and Flora with deep fjords and valleys and with high moun- within less than 300-600 years. This rate of ice tains between. This means that the ice retreats from retreat, and a similar rate of ice advance, may be the coast and landwards occurred mainly through slowed down considerably, to half size or less, and calving along the fjords, which generally is a very the glacial system would still be very dynamic and rapid process, and the ice advances are initiated still in agreement with the model described by from numerous ice growth areas between the fjords Olsen et al. (2001a). The model may therefore be

Fig. 3: Location of sites where the OSL dating samples were taken (Øysand, Langsmoen, Flora), shown in a regional perspective. Trondheim and the adjacent fjord are in the northwestern corner. The Norwegian-Swedish international border that also forms the water divide is shown on right.

4 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Fig. 4: Location of the Flora, Langsmoen ad Drivvollen sites in the Nea River valley, with indication of the main regional ice flow direction and the position of a damming ice barrier in the valley at some point in the history of deposition of sediments at Flora. characterized as robust and not sensitive to small which drains into Selbu Lake which in turn drains and moderate changes in ice retreat and ice ad- into the Nid River which flows to the port city of vance rates. Trondheim on Trondheim Fjord. The Flora section is located at 63° 6' 46"N, 11° 18' 29"E, the Langsmoen section is located approximately 4 km Methods down-valley at 63° 8' 5"N, 11° 15' 29"E, and the Drivvollen section is located midway between Stratigraphy and sedimentology Langsmoen and Flora sections. The watershed In this study we have focused on three stratigraphic divide for the headwaters of this valley, and the sites, the Flora, Langsmoen and Drivvollen sec- Norway-Sweden border is located ~50 km up- tions, within the Selbu region of central Norway valley from the sections. (Figs. 1, 3 and 4) approximately 120 km east- The sections at the Flora site were studied for southeast of the city of Trondheim. The sections the first time in 1997 and at Langsmoen and Driv- are located in the Nea River valley (relief ~300 m) vollen three years later. The sections of the Flora

5 Timothy F. Johnsen, Lars Olsen and Andrew Murray

and Langsmoen sites were exposed by sliding and Dating, where the OSL measurements were also removal of surficial slope material due to heavy completed. rain which followed a short time after removal of The samples were analyzed using large (8 mm) trees and other slope-stabilizing vegetation. The and small (2 mm) aliquots of quartz, ranging in sections at Drivvollen were exposed by road exca- mean grain size from 83 to 170 m, on Risø vations. Sediments were studied using standard TL/OSL-readers equipped with calibrated 90Sr/90Y observational techniques – sediment texture and beta radiation sources (dose rate 0.089-0.32 Gy/s), structure, paleoflow direction indicators, bed con- blue (470±30 nm; ~50 mW/cm2) and infrared (880 tact relationships and lateral continuity and thick- nm, ~100 mW/cm2) light sources, and detection nesses of units – and lithofacies were identified and was through 7 mm of U340 glass filter (Bøtter- interpreted based on their characteristics and asso- Jensen et al. 2000). Analyses employed post-IR ciations, following sedimentologic principles (e.g., blue SAR-protocols (Murray and Wintle 2000, Middleton and Hampton 1976, Allen 1982). 2003, Banerjee et al. 2001), adapted to suit the samples based on dose recovery and preheat ex- Sampling, preparation and measurement periments (preheat 260° for 10 s, cut-heat 220°). The OSL dating technique is used to estimate the 100 s of illumination at 280° between cycles im- time elapsed since buried sediment grains were last proved recuperation (response to zero dose). Some exposed to daylight and is a reliable chronological of the small aliquots were measured using a short- tool, reflected in its growing popularity in Quater- ened IR blue SAR-protocol to increase measure- nary studies (Murray and Olley 2000, Murray and ment productivity. The shortened protocol had Wintle 2000, Duller 2004, Lian and Roberts 2006, three regenerative doses, selected to bracket the Wintle 2008). equivalent dose. The third dose was a recycled Five OSL samples were collected in August dose, and since recuperation rarely was greater 2005 and June 2007 for the Langsmoen and Flora than 5% using the full SAR-protocol, we excluded sections at the levels indicated in Figs. 5 and 6. The the zero dose measurements from the shortened sites were overgrown with herbaceous and shrub protocol. vegetation since the original detailed stratigraphic Dose rates were calculated from gamma spec- work was completed but the stratigraphic units trometry data (Murray et al. 1987) and included the could nonetheless be identified securely. In addi- cosmic ray contribution (Prescott and Hutton tion, a sample of young fluvial sediment was col- 1994). Water content (weight percent) was meas- lected from the riverbank at the mouth of the Gaula ured in the laboratory by weighing re-compacted River at Øysand (Fig. 3; 63° 20’ 27”N, 10° 13’ sediment at natural, saturated and dry water con- 44”E; ~13 km south-southwest of Trondheim; at a tent. The historical water content was estimated to depth of 25 cm) to evaluate if the OSL signals from be 0.75 the saturated water content. This seems fluvial sediments in this region are adequately reasonable given that the sections are located on bleached (i.e., zeroed). These sediments are ex- valley walls that are subject to significant ground- pected to be less than 1 ka old and to have been water flow during parts of the year. Also, sedi- transported at least 5 km from a landslide area ments in these sections have been observed at vari- upstream (Sveian et al. 2006). ous times during spring and autumn to be quite The samples were collected using opaque plas- wet, although their locations are well above the tic tubes and stored in an opaque box until opened local groundwater level and the sediments appear under darkroom conditions at the Nordic Labora- to be quite dry during the summer season. tory for Luminescence Dating (2005) or Stockholm Samples for radiocarbon dating from Flora were University (2007) where samples were apportioned taken from positions well inside the fine-grained and wet sieved. Final preparation, including heavy units and therefore well away from potentially liquid separation (2.62 g/cm3) to remove feldspars, contaminated surfaces. Water flow through the treatment with 10% HCl for 5-30 minutes, 10% sediments was not a major problem for the radio-

H2O2 for 15-30 minutes, 38% HF for 60-120 min- carbon dates, because the water flow goes mainly utes and 10% HCl again for 40 minutes was per- through the adjacent coarse grained sediments and formed at the Nordic Laboratory for Luminescence may therefore contaminate the boundary surfaces

6 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Fig. 5: Generalised stratigraphic log from Flora, based on several sections which are partly separated, both in height and width, but located within a 200m by 300m area in the valley side (see Fig. 4). Shown are the location of eight radiocarbon samples and cali- brated ka age (black dots) and OSL sample 071301 (open circle ‘01’ at 252 m). Till fabric location indicated by circles with cross; solid arrow and value indicate the direction of the main cluster of data; dashed arrow is direction based on less than 25 clasts.

7 Timothy F. Johnsen, Lars Olsen and Andrew Murray

Fig. 6: Generalized stratigraphic log from the combined section based on several, small, overlapping sections in height and width at Langsmoen. Shown is the location of four OSL samples with the ka age using large and small aliquots (number inside circle is the last two digits of the sample number; see Table 3 and 4). Till fabric location indicated by circles with cross; solid arrow and value indicate the direction of the main cluster of data.

8 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

of fine-grained sediment units, but probably very unity. The first step was introduced to address little inside the fine-grained units. As well, there aliquots with poor recycling ratios that would be were no visible traces of oxidation, root penetra- accepted because they had unacceptably large un- tion, or fissures within the sampled sediment. certainties (~>30%). Aliquots also had to pass the Samples were air dried and stored in a cold room following rejection criteria: recuperation <5%, with a temperature of 0-4°C to avoid bacterial equivalent dose error <50% and signal more than contamination (e.g., Wohlfarth et al. 1998). Sam- three sigma above the background. Decay and ples were measured at the Accelerator Mass Spec- growth curves also had to be regular. More conser- trometry (AMS) facility at the University of vative rejection criteria values were used for the Utrecht, which uses a 6 MV Van de Graaff tandem shortened protocol employed for some small ali- accelerator (van der Borg et al. 1997). Graphite quots; they were scaled appropriately based upon targets were used for the AMS analysis. A standard the actual structure of the sequence used. Ages for alkali-acid-alkali treatment was used to remove all samples were calculated using the mean and contamination by humic acids and carbonate. After median of the equivalent dose population of ac- combustion of the organic carbon samples, the cepted aliquots for each sample, as well as using obtained CO2 gas was routinely separated from the dry and saturated water contents. SO2 with KMnO4 (see Olsen et al. 2001c and refer- A sensitivity analysis was also performed to de- ences therein). The insoluble fraction was used to termine quantitatively which uncertainties have the derive the sample age. At Langsmoen it was more largest effect on the age. Using reasonable esti- difficult to find fine-grained units that were thick mates of uncertainty for each parameter, ages were enough to avoid a potential contamination prob- recalculated after adjustments were made to each lem, and therefore we have no radiocarbon dates of the parameters in turn. The estimated uncertain- from this site. ties (1 standard deviation) used for each parameter As we were calibrating radiocarbon dates (i.e., in these calculations were: depth below surface ±1 interstadial dates) from the literature that were well m, elevation ±50 m, grain size ±20%, water content beyond the calibration curve IntCal04 (Reimer et (gamma and beta) ±20%, dose rate gamma ±5%, al. 2004), we used Fairbanks et al. (2005) with the dose rate beta ±5%, internal dose rate ±30%, den- calibration curve Fairbanks0107 for all radiocarbon sity ±10%, cosmic ray contribution ±5%, and beta dates. Note that calibrations using IntCal04 versus source calibration ±2%. Fairbanks0107 of radiocarbon dates from Flora section produced calibrated ages differing by less than one percent. Results

OSL data analysis The Flora, Langsmoen and Drivvollen stratigraphic sites Simple component analyses of the continuous wave OSL data from selected aliquots was under- The Flora site taken using SigmaPlot 10.0, based on the parame- The Flora site consists of several sections within a ters and formulas of Choi et al. (2006). The results 200 m by 300 m area in the valley side (Fig. 4). of the component analysis are discussed further The four main sections are situated 337-340 m below, but based on such information from dose a.s.l., 301-310 m a.s.l., 270-280 m a.s.l., and 252- recovery measurements we chose the 0-0.64 s and 265 m a.s.l. (Fig. 5 and Table 1). The lowest-lying the 0.96-2.08 s portions of the signals for peak and of these was later extended to bedrock by excavat- background integration limits for all aliquots. The ing mainly through a boulder-rich lower till and a equivalent doses were then calculated in Risø Lu- coarse-grained diamicton, probably a till, with minescence Analyst 3.24 (using exponential curve heavily weathered material at the base. The vertical fitting) and in Microsoft Excel. intervals between the main sections have not been Aliquots were initially accepted when (1) the fully excavated and cleaned, but have been absolute value of the recycling ratios was within checked with the help of a spade and a 1 m-long the range 0.7 to 1.3, and (2) when accounting for drilling rod with a 1 inch-wide track for sediment their uncertainty their value was within 15% of sampling. This is done to make sure that no inter-

9 Timothy F. Johnsen, Lars Olsen and Andrew Murray

Table 1: Sedimentary diamict and other lithofacies used in Figures 5 and 7. Modified from Olsen et al. (1996). Code Facies description Interpretation Dcs Clast supported diamicton, stratified, occurrence often in combination with S-Ablation melt-out till and poorly sorted glacifluvial debris flow/ debris fall , G-, sDm-, gDm-, and Dms-facies. material. Dmm Matrix supported, massive, normal silty-sandy composition. Variable clast Till or debris flow deposits (and also some glacimarine sediments). fabric from random to strong parallel or occasionally transverse. Dmm(s) Dmm with dense internal shearing, often with strong parallel clast fabric. Lodgement till.

Dmm(r) Dmm with evidence of resedimentation, often medium strong to strong Mainly lodgement and basal melt-out till. parallel clast fabric. Dms Matrix supported, stratified diamicton, with sand lenses and linings around Mainly basal melt-out till, but often combined with intervening or alternating clasts. Medium to relatively strong parallel clast fabric, transverse fabric may zones of lodgement till. occur in some areas. Dms(r) Dms with evidence of resedimentation, for instance with rafts of deformed Mainly basal melt-out, but often combined with zones of lodgement till. sand/silt/clay laminae and abundant silt/clay stringers and rip-up clasts. Clasts fabric variable from random to fairly strong. sDm Sand-enriched matrix supported diamicton, mainly massive (sDmm), but Tillised sediment/deformation till containing sand eroded from local substrate; occasionally heterogeneous or stratified (sDms). and melt-out till. gDm Gravel-enriched matrix supported diamicton, mainly massive, but Mainly melt-out till, but in some cases possibly also tillised sediment or occasionally heterogeneous or stratified. deformation till with gravel eroded from local substrate. cDm Cobble- and boulder-enriched matrix supported diamicton, mainly massive, Mainly melt-out till, but in some cases possibly also tillised or deformed but occasionally heterogeneous or stratified. sediment reworked from local substrate. FSi Fine silt Vertical accretion by settling of sediment from suspension in quiet water lakes Si Silt (glaci-/lacustrine) and marine basins. This include FSi, Si, CSi, FS, and often CSi Coarse silt also S/SSi facies. FS Fine sand S/SSi Sand/ Sand, silt Lateral accretion, sediments supplied by traction with fallout, glaci-/fluvial and CS Coarse sand marine coarse-grained sediments. This include S/SSi, CS, and G/GSi/GS facies. G/GSi/GS Gravel/ Gravel, silt/ Gravel, sand D Diamicton Till/ mudflow/ debris flow/ and debris fall material, mainly. Sil/Sild Silt, laminated/ Sil, deformed Fallout with or without traction, quit water/ later deformation. Si(r) Silt, resedimented Erosion and resedimentation, varied environments. Sl/Sm Sand, laminated/ Sand, massive Settling from suspension, shifting -/ increased sediment supply. Sld Sand, laminated, deformed Laminated sand, later deformed by glacial processes, mainly. Sp/Spd Sand, planar bedding/ Sp, deformed Fallout with or without traction, quit water/ later deformation.

vening main sediment unit is missing in the strati- deformation, occur also in unit E3. This unit is graphic record. overlain by a brownish-grey till of, at least, 10 m The ~25 m high lowermost section starts with a thickness. It is separated in three parts, D1, D2 and 1-4 m thick coarse-grained gravelly sandy diamic- D3, by intervening silt and sand horizons E1 and ton, which is inferred to be a till, at the bedrock E2. The matrix of tills D1, D2 and D3 changes between ~240 and 245 m a.s.l. (Fig. 5; unit G). The with a general fining-upwards trend from gravelly bedrock is mica schist, with a glacially striated sandy in till D3 to sandy in till D2 and more silty in surface partly preserved. The striation indicates ice till D1. The compactness of these tills increases as flow towards 280°. In other parts the bedrock is the matrix changes upwards to a more fine-grained weathered and some of the weathered material has character. Overlying these tills follows again sev- been reworked in the till. Overlying the lowermost eral metres (50-60 m) of till in beds (subunits B1, till follows a 7-8 m-thick silty, sandy, compact, B2 and B3) alternating with laminated sand and silt brownish-grey to greenish-grey till (unit F) with (subunits C1, C2 and C3) of thicknesses from a many cobbles and boulders. Clast fabrics in these few centimetres to one or several metres. Tills B1, two lower tills indicate preferred maxima between B2 and B3 are all relatively compact and mainly 280° and 305°, which correspond with striation on silty and dark grey in colour, with a bluish-grey bedrock as well as on a big boulder in the contact tone in most parts of tills B1 and B2. zone between the tills. Overlying these tills follows The Flora site is completed on top by a 3 m- unit E3 (Fig. 5), which is a 4.5 m-thick series of thick sequence of two coarse-grained, brownish- alternating layers of laminated sand and silt in a grey and medium to loose compacted tills (Fig. 5; number of fining-upwards sediment successions. unit A). Full fabric analyses have not been per- Thin irregular layers of diamict material or grav- formed in the tills younger than D3, but the orien- elly sand, as well as some indications of glacial tation of some 15-20 clasts and a few fold-axes

10 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Table 2: Flora section AMS radiocarbon ages of sub- tively. Unit D could alternatively be described as a till waterlain sediments (from Olsen et al. 2001c) . four fining-upwards sequences, with other bounda- Lab no. Elevation 14C age Calibrated age ries for each sub-unit than illustrated in Fig. 6. The (m) (yr BP) (yr BP)b gravel and sand are deposited in layers sloping in

1 UtC 5977 309 17800 ±400 21100 ±1000 the downstream direction towards the north. De- 2 UtC 5978 309 15920 ±260 19100 ±400 formation structures like sediment injections and 3 UtC 5979 305 17800 ±400 21100 ±1000 folding are increasing in size and frequency up- 4 UtC 5981 273 16700 ±220 19800 ±600 5 UtC 5982 272 15620 ±200 18800 ±400 wards in the upper three subunits D3-D2-D1, with 6 UtC 5984 260 19600 ±280 23400 ±800 only small deformation represented in the bounda- 7 UtC 6042 255 19050 ±120 22600 ±200 8 UtC 5985 253 18000 ±400 21400 ±1200 ries of subunit D3, whereas overturned layers of mean = 20900 sand dipping steeply, almost vertically towards the stdev = 1600 northwest occur in subunit D1. The silt in subunit

Notea: All were measured using the insoluble fraction. D3 contains foraminifers of e.g. Cibicides lobatu- Noteb: Calibrated using Fairbanks et al. 2005. Note that calibrations lus and Elphidium excavatum (Olsen et al. 2002). differ by less than 1% from OxCal 4.0 and the IntCal 04 calibration curve (Ramsey 1995, 2001, Reimer et al. 2004). Uncertainty shown is All the C. lobatulus foraminifers indicate some at 1. corrosion or dissolution, possibly due to the effect of various environments during resedimentation from upstream, older strata (of probably Eemian age). The few other species show no sign of corro- from glacial deformation at three levels in the up- sion and may belong to the last phase of deposition per 65 m of the Flora stratigraphy have helped to and, therefore, indicate marine influence in these indicate approximate ice flow directions (stippled sediments. arrows in Fig. 5). All these are trending towards Overlying the waterlain sediments, which are the NW. thought to be fluvial deltaic in origin, follows two Radiocarbon dating of bulk organics from the till beds with less than 1 metre of sandy slope ma- silty sediments was performed at eight levels from terial on top (Fig. 6). The lower till, unit C is rela- five of the silt and sand horizons between 309 and tively compact, with a sandy-silty matrix and some 252 m a.s.l. (Fig. 5). The mean and standard devia- boulders, cobbles and pebbles, and a brownish- tion of the ages from Flora are 20.9 ±1.6 cal. ka BP grey colour. The upper till (unit B) is more silty, (Table 2). Also, based on microscopic and stereo- darker grey to bluish-grey and very compact. Till scopic examination of parallels to most of the dated fabrics indicate preferred clast orientation towards bulk-organic sediment samples, terrestrial plant the NW and NNW for these tills, quite similar to remains are the main organic component for these the regional ice flow direction based on striation samples. OSL results for the Flora and Langsmoen and drumlin orientation (Figs. 4 and 6). sites are presented in detail in section OSL charac- teristics and ages. The Drivvollen site Fresh road cuts along a local road at Drivvollen The Langsmoen site (Fig. 4; Olsen et al. 2002), midway between A 15-17 m high section which was comprised by Langsmoen and Flora, revealed in the year 2000 a several 1-2 m wide and 2-3 m high sections that stratigraphy comprising both the till units recorded were overlapping in height and width is represent- at Langsmoen and an underlying glacifluvial/ flu- ing the Langsmoen site (Fig. 6). The lowermost vial/ fluvial marine gravelly and sandy sediment sedimentary unit here, unit D, is divided in four unit that may correlate with the Langsmoen sub-till subunits D4, D3, D2 and D1, where D4 is mainly deltaic sediments. At Drivvollen, these sediments gravel and sand, and D2 is gravel. Subunits D3 and reach up to 215-220 m a.s.l. (Figs. 4). D1 are silt and sand with some silt-layers, respec-

11 Timothy F. Johnsen, Lars Olsen and Andrew Murray

Table 3: Langsmoen OSL sample properties; listed in order of sample number. Flora section results at bottom (sample 071301). Note that the text sometimes refers only to the last two digits of the sample number.

Water content (weight %) Sample Elev (m) Sampling Lithofacies sampled Saturated Selected a Mean grain depth (m) size used

071302 210 8.0 Deformed, laminated sand 34.7 26.0 85 081357 200 18.0 Diffusely graded sand with silty clay rip-ups 33.2 24.9 94 081358 208 10.0 Deformed, laminated sand 31.0 23.3 122 081373 210 8.0 Deformed, laminated sand with massive, matrix-supported diamicton 24.2 18.2 170 071301 252 35.0 Deformed, diffusely graded sandy silt 17.0 12.8 83

Notea: Selected water content estimated to be approximately 0.75 the saturated water content.

OSL characteristics and ages indicate that the selected time intervals for peak and background integration resulted in a signal that The major sample properties, settings and results was dominated by the fast component. Doses cal- are listed in Tables 3 and 4, and Figs. 7 to 11. The quartz from Langsmoen and Flora sections is in- culated with this peak and background selection gave good dose recovery (1.06 ±0.03, n = 18, un- sensitive with photon counts less than 1000 for the certainty as the standard error; Fig. 9) and demon- first 0.08 s of stimulation (Fig. 7, insets), which leads to larger uncertainties (cf. Alexanderson and strate that the SAR protocols used were able to accurately recover a known dose given before any Murray in press). Careful selection of peak and heating. The signals from the Flora section were background channels was made (0-0.64 s and 0.96- 2.08 s portions, respectively) to best isolate the fast close to saturation, from the flattish part of the extended growth curve, while signals from the component (Fig. 8). For the eighteen accepted dose Langsmoen section were from the steep, near- recovery experiments the average proportion of the net component signal to the total net signal used linear, early part of the extended growth curve (Fig. 7). This has implications for the reliability of for dose calculation was: 95 ±6% (fast), 5 ±5% the final ages, see Discussion. (medium), and 0.3 ±0.6% (slow). These results

Table 4: Langsmoen OSL sample results and ages. Flora section results at bottom (sample 071301).

Age

Sample Aliquot nDose rate Estimated Recycling Mean Median Drya Saturated Skew 2 x SE of size (mm) (Gy/ka) dose (Gy) ratio skewnessb

071302 8 22 1.81 ±0.07 37.5 ±2.3 1.09 ±0.10 20.7 ±1.6 19 16.1 ±1.3 22.1 ±1.7 0.35 1.04 071302 2 66 1.81 ±0.07 38.6 ±1.8 1.02 ±0.10 21.3 ±1.4 21 16.6 ±1.2 22.8 ±1.4 0.03 0.60 081357 8 26 1.51 ±0.07 33.9 ±1.3 0.95 ±0.14 22.5 ±1.4 22 17.6 ±1.2 24.1 ±1.5 0.48 0.96 081357 2 49 1.51 ±0.07 35.3 ±1.7 1.06 ±0.17 23.4 ±1.6 24 18.3 ±1.4 25.1 ±1.7 -0.35 0.70 081358 8 18 2.01 ±0.08 41.4 ±2.5 1.02 ±0.18 20.6 ±1.5 20 16.4 ±1.3 22.0 ±1.6 0.59 1.15 081358 2 20 2.01 ±0.08 45.0 ±2.4 0.98 ±0.15 22.4 ±1.6 23 17.8 ±1.3 23.9 ±1.6 -0.74 1.10 081373 8 37 2.01 ±0.09 51.0 ±2.0 1.02 ±0.12 25.4 ±1.6 25 21.2 ±1.4 26.7 ±1.6 0.64 0.81

071301c 8 41 1.62 ±0.08 164.8 ±6.6 1.03 ±0.07 101.5 ±6.6 106 88.4 ±6.1 105.7 ±6.8 -0.34 0.77

Notea: The "Dry" age represents the age of the sample when it contains no water, whereas the "Saturated" age represents the age of the sample when it is saturated with water. Together these represent the maximum age range when considering the water content. Noteb: Two times the estimated standard error of skewness derived using 2 x SES = SQRT(6/N) (Tabachnick and Fidell, 1996). Note that none of the samples are skewed to a significant degree as the skew is less than two times the standard error of skewness - except for sample 071301 (see note c below). Notec: Sample 071301 from the Flora section had many aliquots that gave estimated doses far beyond the highest regenerative dose and so were not used in the calculations. Thus, the estimated dose and apparent ages are underestimated, and skewness is negatively biased.

12 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Fig. 8: Using data from the 18 dose recovery experiments, peak and background channels were chosen that provided the overall best recycling and dose recovery, and a dominance of the fast component after background subtraction. Example of signal component analysis from sample 081357 showing the natural signal deconvoluted into the fast, medium and slow components (left axis), and the natural and modeled (sum) signal (right axis). Also shown are the peak and background portions of the signal used (0-0.64 s and 0.96-2.08 s). Note that only the first 5 s of 40 s total stimulation are shown. Deconvo- lution of dose recovery data indicated that the channel selec- tion effectively isolated the fast component and the selection of peak and background channels provided the optimum recy- cling and dose recovery.

sample is 165 Gy and 1.6 Gy/ka respectively (Ta- Fig. 7: Single-aliquot regenerative-dose (SAR) OSL growth ble 4). Recycling is exceptionally good with a curves for Flora section sample 071301, and Langsmoen section samples 071302 and 081358; first two samples are mean and standard deviation for all samples of average of two aliquots with uncertainties as standard devia- 1.02 ±0.04, n = 8. The age of the Flora section tion. The range of estimated doses used to calculate the age of sample is 102 ka. The seven ages from large and each sample is indicated by the width of the grey shading; the small aliquots from the Langsmoen section range mean equivalent dose is also shown (black triangle). Note that equivalent doses for 071301 (from the Flora section) have a between 25.4 to 20.6 ka with a mean and standard large range and are from the flatter part of the growth curve. deviation of 22.3 ±1.7 ka. The ages from the large Repeated dose points (open squares) and a zero dose point and small aliquots for the same sample are similar (open circle) are also shown. The inset shows the natural decay and overlap at 1. With the exception of the Flora curve; the decay curve for the young sediment sample from Øysand (081360) is also shown in inset for 081358 (sediment section sample, the distributions of the equivalent dose rate of 1.7 Gy/ka). doses used to calculate the age are not significantly skewed (Table 4, see footnote). The sensitivity analysis demonstrates that the calculated age is For the Langsmoen section samples, equivalent most sensitive to changes in the equivalent dose, doses range between 34 and 51 Gy and dose rates beta source calibration and dose rate, followed by between 1.5 and 2.0 Gy/ka, while for the Flora water content (Fig. 11).

13 Timothy F. Johnsen, Lars Olsen and Andrew Murray

no marine fossils have been found in these sedi- ments. The radiocarbon datings, with a mean and stan- dard deviation of the ages of 20.9 ±1.6 cal. ka BP (Table 2), indicate that all the glacial and glacio- lacustrine oscillation phases occurred during what is traditionally thought of as the LGM interval (Fig. 5 and Table 2). The results from this site along with other dated sub-till sediments in Nor- way define the Trofors interstadial, which is brack- eted by the LGM 1 and LGM 2 stadials (e.g., Olsen et al. 2001a, Figs. 2 and 10).

The Langsmoen site The interpretation of the Langsmoen stratigraphy is that it represents a phase of considerable ice retreat with fluvial deltaic sedimentation, possibly with some marine influence at the site, followed by Fig. 9: Histogram of dose recovery tests, excluding aliquots phases of glacial advances during the last glacia- that did not pass rejection criteria. As the mean is close to unity, this indicates that the samples can be used for OSL- tion. The coarse-grained lower till and the fine- dating with our analytical protocols. grained upper till here are texturally similar and with clasts of similar lithology and are therefore probably correlative to the coarse-grained, brownish-grey lower till and the fine-grained, blu- ish-grey tills, respectively, at Flora. However, the Discussion waterlain, sub-till sediments at these two localities are different, with ice-free conditions at Stratigraphy and paleoenvironment Langsmoen and ice proximal and ice-damming The Flora site conditions represented at Flora. These different environments may have occurred during the same The interpretation of the Flora stratigraphy is that it interval, and even possibly with ice temporarily represents a succession of repeated glacial ad- acted as a damming barrier between the localities vances alternating with repeated phases of ice- (Figs. 4 and 12). The content of plant remains and damming with pulses of sand and silt flowing into other organics is, however, not sufficiently high in lateral or subglacial glaciolacustrine basins. All the the Langsmoen sub-till sediments to allow testing waterlain sediments (E and C subunits) are thought of this hypothesis by radiocarbon dating. The rela- to represent the same sedimentary environment, a tive sea level during deposition of the Langsmoen glaciolacustrine/ ice-dammed lake environment. waterlain sediments was higher than 210 m a.s.l., For example, the 4.5 m-thick series of alternating which corresponds with the elevation of the eroded layers of laminated sand and silt in a number of top of the sub-till deltaic foreset beds at fining-upwards sediment successions that comprise Langsmoen. The relative sea level was probably at unit E3 are thought to represent repeated melt- least 220 m a.s.l., in agreement with the elevation water-pulses into an ice-dammed lake environ- of the top of similar and possibly correlative fluvial ment. Small amounts of plant remains in the sedi- beds, also with marine influence at the neighbour- ments indicate that at least some vegetation may ing Drivvollen site (Fig. 4, Drivvollen; Olsen et al. have been established during the phases of ice 2002). This is ~10% higher than the late- retreat. The relative sea level during deposition of /postglacial marine limit in this area. the Flora waterlain sediments is not known, except that it was probably lower than 252 m a.s.l. since

14 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Fig. 10: Graphical summary of OSL ages for all Langsmoen section samples, including large and small aliquots; corresponding recycling ratios below. Age calculated from the population of accepted aliquots using the mean, median, no water content, and saturated water content. Error bars represent one standard error. The mean of the ages is 22.3 ±1.7 ka (uncertainty as standard devia- tion which ranges from 24.0 to 20.6 ka). The ages are reasonably consistent and correspond very well to the Trofors interstadial, ~25 to 20 ka (Olsen et al. 2001a). Stadials (grey) and interstadials (white) indicated on the right.

Ice flow directions which is in agreement with the main regional ice During initial ice growth and final decay of the last flow direction (Figs. 4 and 6). ice sheet, the ice flow has followed the main trends The general glacial stratigraphy model of most of the valleys and fjords. In the region east of valleys in Norway is characterized, not only with Trondheim (Fig. 3) this resulted in a dominating more of local materials, including more weathered ice flow direction during these phases towards the material in the lower tills, but also often with more west and northwest. During maximum phases, the coarse-grained material. The general increase of ice sheet was thicker and the ice flow was less fine-grained material in younger tills is thought to influenced by the underlying topography, and was derive from more long-transported material which trending towards the northwest and north- has been crushed and abraded during a longer northwest in this region. transport history. During deglaciation the youngest Westerly to northwesterly trending ice flow di- tills may again include more coarse-grained mate- rections are inferred from striation on bedrock and rials, which may derive from ice-margin oscilla- boulders at Flora and till fabrics in the lower tills tions and a changed pattern of erosion, transporta- and deformation in the sub-till sediments at both tion and deposition. The total Flora glacial strati- Flora and Langsmoen. These ice flow directions graphy shows this trend, and therefore seems to be are in best agreement with phases during ice in concert with the general model. Therefore, it growth or final decay of the ice sheet. Till fabrics seems likely that the lower tills have been depos- indicate that the fine-grained, dark bluish-grey ited during ice growth, whereas the younger tills upper tills at both sites may be a result of a more derive from later phases. Of course there may be northwest to north-northwesterly trending ice flow, exceptions from the general model in some loca-

15 Timothy F. Johnsen, Lars Olsen and Andrew Murray

Fig. 11: Sensitivity analysis showing by how much the OSL age will change by percent change in a given parameter for sample (071)302, large aliquots (age = 20.7 ka). Steeper slopes indicate that the age is more sensitive to changes in the given parameter. Noteworthy is that the age is most sensitive to changes in the equivalent dose, beta source calibration and dose rate, followed by water content. The x-axis range of a parameter’s line is its 2 uncertainty. Quite similar results were acquired for the other samples. tions, but to really test this hypothesis carefully at plete bleaching, as it is not reasonable to expect each site requires much more detailed work. sediments from different portions of the section to suffer the same degree of incomplete bleaching to OSL and ages produce similar ages. Also, if there were bleaching Of primary importance in employing OSL dating problems we would expect measurements on small in glacial and glacially-related sediments is to de- aliquots to produce positively skewed dose distri- termine whether the sediments were adequately butions or at the very least a significantly younger exposed to light prior to deposition; otherwise the age (Fuchs and Owen 2008, and references ages will be maximum ages (Murray and Olley therein); neither is the case (Table 4), and the ages 2000, Fuchs and Owen 2008, Alexanderson and from large and small aliquots from the same given Murray in press). The good correspondence in age sample overlap within 1. In addition the very low between samples, between large and small aliquots, OSL signals from young fluvial sediments at Øy- between mean and median values, and the insig- sand indicate that fluvial sediments in this region nificant skewness strongly indicate that the can be properly bleached (see sample 081360 in Langsmoen sampled sediment was adequately bottom inset of Fig. 7). exposed to light (i.e., “well-bleached”, or “zeroed”) Based on that sample 081373 contained some prior to deposition (Table 4, Fig. 10). This also diamict sediment, which may have been derived justifies the use of the mean age and not for exam- from subaqueous debris flow or till tectonized into ple a minimum age model for the small-aliquot the fluvial sediments, there is a risk for incomplete data (Galbraith et al. 1999). Besides, it is very bleached grains to be incorporated. This sample is unlikely that all the samples suffer from incom- also slightly older than the others (Table 4, Fig.

16 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Fig. 12: Long-valley profile cartoon showing the relationship between stratigraphic sites and the ice dam at Hoggkjølen (see Fig. 4).

10). As we measured only large aliquots for this lowest equivalent dose for this sample gives an sample, the dose distribution unfortunately cannot apparent age of about 45 ka, which is well beyond be used to evaluate skewness-effects of incomplete the 21 ka (n = 8) radiocarbon age of the Flora bleaching (as there is a large averaging-out effect sediments. Thus it is very likely that the glacio- for large aliquots; Duller 2008). Nevertheless, on lacustrine sediment from Flora is poorly-bleached the whole we conclude that the Langsmoen sam- and therefore we reject its OSL age (Wallinga ples were well-bleached before deposition. 2002). In contrast, the Flora section sample gave an er- The sediment dose rates for the various samples roneously old age based on comparison to the eight (1.8 ±0.2 Gy/ka) were quite consistent and suggest radiocarbon dates (Fig. 5). This is anticipated as it that there is not a significant problem with the is not expected that glaciolacustrine sediments sediment dose rates measured (Table 4). Finally, would be adequately bleached prior to deposition the water content history of the sampled sediment (Alexanderson and Murray in press), especially if can only be estimated. As stated earlier, our best the ice-front was nearby or if sediments were de- estimate is that over their lifetime the sediments rived from a submerged ice-front. Unlike the well- experienced on average ~75% their saturation. bleached Langsmoen sediments, the equivalent Despite this limitation the sensitivity analysis indi- dose population for the Flora sediment is very cates that even with a 20% change of the percent broad and from the flattish, high dose, portion of water content values, ages change by less than ~3% the growth curve (Figs. 8 and 10, Table 4). Note (Fig. 11). that many aliquots gave equivalent doses well The radiocarbon dates from the Flora section beyond the highest regenerative dose as well, and are considered to be reliable as (1) sampled sedi- were not included in the determination of the ments were derived from the interior of laminae or equivalent dose; thus the dose population would be beds that were adjacent to more hydraulically con- even wider than portrayed in Figure 8. Even the ductive sediments, thus minimizing possible

17 Timothy F. Johnsen, Lars Olsen and Andrew Murray

groundwater flow and contamination through the during the Andøya – Trofors interstadial was sampled sediment, (2) the ages are consistent over probably cold to boreal (Vorren et al. 1988, Alm the 54 meter range of the section, which is unlikely 1993, Olsen et al. 2001b) with arctic to subarctic to occur if groundwater contamination was an conditions where the mollusc Mya truncata, which important process, (3) the ages fit well with similar is a temperate Atlantic water indicator, reached dates from other sites throughout Norway that northwards at least to the southern coast of Norway belong to the Trofors interstadial, and finally (4) (Olsen and Bergstrøm 2007). the ages are in agreement with the OSL ages from The geographical extensive distribution of Tro- sub-till sediments from the nearby Langsmoen fors interstadial sediments, as well as that for the section. Terrestrial plant remains, which appear to Hattfjelldal I and Hattfjelldal II interstadials (Fig. be the main organic constituent of the dated mate- 3), indicates that causes behind these interstadials rial, are considered to be reliable for radiocarbon were regional in nature. In addition, the very dy- dating, and are supported by the agreement be- namic ice sheet fluctuations exceed rates of change tween the radiocarbon and OSL ages. that could be brought on by air temperatures changes alone. Thus, in addition to precipitation, Implications for ice sheet history and the mountainous fjord and valley topography, gla- dynamics cial isostasy and relative sea level changes were The seven OSL ages of the Langsmoen section probably more important for the size of the glacial sediments of 22.3 ±1.7 ka correspond very well to fluctuations than were air temperature changes. the Trofors interstadial of ~25.2 to 20.1 ka which is This statement is simply based on that the fjord and based on 40 radiocarbon ages including eight from valley topography, considerable glacial isostatic the Flora section of 20.9 ±1.6 cal. ka BP (Fig. 10, depression and high relative Middle to Late Table 2; Olsen et al. 2001b). Thus, the OSL ages Weichselian sea levels are all documented and from the Langsmoen section support the results of obvious important factors for ice sheet margin the AMS radiocarbon dating method on glacial fluctuations (e.g., Olsen and Grøsfjeld 1999), sediments with low organic content (Olsen et al. whereas air temperature changes may be balanced 2001c), and confirm the occurrence of the Trofors with precipitation so that the glacier fluctuations interstadial in central Norway which also has been are reduced, as seen from many modern glaciers. identified elsewhere in Norway (Fig. 1). The simi- Would the ice sheet fluctuations recorded along larity in age within and between these stratigraphi- the western margin of the Scandinavian ice sheet cally-related sites and using different geochro- also occur in other areas of the ice sheet? Argua- nological techniques strongly suggests that this bly, ice streams, especially widespread in Norway, area was ice-free around ~21 or 22 ka. played a very important role in the dynamics of the The ages of the Langsmoen and Flora section Scandinavian ice sheet (Fig. 1), especially as they sediments fall within the early to middle portion of would be sensitive to relatively small changes in the Trofors interstadial (Fig. 10). We imagine a relative sea level and would be very effective at paleoenvironment whereby the Langsmoen gla- removing mass from more interior areas of the ice ciofluvial sediments (at 200 to 210 m a.s.l.) were sheet and encourage retreat from both lowlands deposited in ice-distal conditions with local sea and high elevation (Shepherd and Wingham 2007, level at least 210 m a.s.l., possibly ~215-220 m Hubbard et al. 2009); this is reflected in the re- a.s.l. if the Langsmoen sediments correlate with the gional response of the ice sheet (Olsen et al. nearby Drivvollen sediments as mentioned before. 2001a). We suspect that the south-western areas of Further advance of the ice sheet leading into LGM the ice sheet in Denmark and Sweden may also 2 resulted in ice damming down-valley (Figs. 4 and have responded in a similar fashion to the ice mar- 12) and deposition of till alternating with glacio- gin in Norway (Hillefors 1969, 1974, Lundqvist lacustrine sediments in ice-proximal conditions at 1992, 2004) because like Norway the south- the Flora site with the highest lake level up to 310 western area of the ice sheet was adjacent to the m a.s.l. Further advance of the ice sheet resulted in influencing-effect of the sea and was host to ice the moderate glaciotectonizing of these sediments streams in the North Sea and Baltic Sea (Fig. 1; and their burial beneath lodgement till. The climate

18 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

Houmark-Nielsen and Kjær 2003 and references topography. For example, the Middle Weichselian therein). interstadial was longer lived than the Trofors inter- In Denmark, the Kattegat Till and Mid Danish stadial and consequently is more likely to have Till may correspond to the similarly dated LGM 1 been felt in the more central areas of the ice sheet, and LGM 2 tills in Norway; and the Vennebjerg- and sites at Pilgrimstad in central Sweden, Sokli, Sejerø-Klintholm interstadial, the Lønstrup- Ruunaa, and Hitura in Finland, several sites in Uranienborg-Gärdslöv interstadial and the Ribjerg- Skåne, southernmost Sweden, as well as numerous Fegge-Spøttrup-Glumslöv-Kobbelgård interstadial AMS-radiocarbon dated mammoth finds suggest in Denmark and SW Sweden correspond to the that the ice sheet was either very small or absent Ålesund-Sandnes-Hattfjelldal I interstadial, the during MIS 3 (Figs. 1 and 2, Arnold et al. 2002, Hamnsund-Hattfjelldal II interstadial and the Svendsen et al. 2004, Kjær et al. 2006, Ukkonen et Andøya-Trofors interstadial in Norway, respec- al. 2007, Helmens et al. 2007a, 2007b, Alexander- tively (Olsen et al. 2001b; Houmark-Nielsen and son et al. 2008, in press, Lunkka et al. 2008, Sa- Kjær 2003). While one could assume that higher lonen et al 2008, Wohlfarth 2010). In contrast to elevation areas within southern Sweden may have the Early and Middle Weichselian interstadials, the been influenced less by the draw of ice streaming, Trofors interstadial was of smaller geographical thoroughly dated sediments in southern Sweden extent, shorter-lived, and occurred in the most (Småland, part of the south Swedish highland) give responsive portion of the ice sheet (Figs. 1 and 2). OSL ages with a standard deviation range of the Nevertheless, the Trofors interstadial represents mean from 23.7 to 19.1 ka (Alexanderson and acknowledgement that the Scandinavian ice sheet Murray 2007, in press), and correspond very well was indeed dynamic and that we should be open to to the Trofors interstadial (Fig. 1). the possibility that the existing ice sheets on Earth The marine records include megascale linea- could act dramatically as well. tions that indicate ice-stream activity (fast-moving Recent robust modelling of the nearby British- wet-based ice constrained by slow-moving ice) Irish ice sheet has produced a very dynamic ice localized to many channels, troughs and elongated sheet with numerous binge/purge, advance/retreat basins crossing the continental shelf off Norway (i.e., yo-yo) cycles dominated by ice streaming (e.g., Ottesen et al. 2005). Also included are large (Hubbard et al. 2009); behaviour similarly docu- trough mouth fans comprised of numerous, stacked mented for Norway. The modelled behaviour dem- sediment wedges from debris flows produced at the onstrates alternating periods of relatively cold- ice margin during maximum ice extent (e.g., Vor- based ice, with a high aspect ratio associated with ren and Laberg 1997). These features, and the net growth, and wet-based ice with a lower aspect chronology based on dates of marine fossils in ratio characterized by streaming. Phases of pre- sediments that subsequently have been overlain by dominant streaming activity coincide with periods debris flow sediments, in several stacked marine- of maximum ice extent and are triggered by abrupt debris flow sediment successions, indicate a very transitions from a cold to relatively warm climate, unstable ice margin during the MIS 3 - MIS 2 in- resulting in major iceberg/melt discharge events terval (e.g., King et al. 1996, Nygård et al. 2005, (Hubbard et al. 2009). The fjord-dominated land- Sejrup et al. 2009). scape of Norway and its shelf are in no doubt a We appreciate that it may be difficult for some record of the dominance of ice streams in draining to accept that there was an interstadial during what the Scandinavian ice sheet (Longva and Thorsnes has been traditionally thought of as the Last Glacial 1997, Ottesen et al. 2005). Perhaps the Scandina- Maximum in Scandinavia (now a two part LGM vian ice sheet (at least its western margin) behaved separated by the Trofors interstadial; Olsen et al. in an even more dynamic manner than documented 2001a). Perhaps it is easier to accept by examining so far, similar to the British-Irish ice sheet. Argua- the dynamics of the ice sheet over a longer time bly the modelling has exceeded the practicalities of scale. Large ice retreats occurred after moderate to the field science as dynamic ice sheet conditions large ice advances during the Early and Middle mean that it is difficult to find sediments from Weichselian (Mangerud 2004). These retreats and earlier ice-free periods that have survived subse- advances stretched over vast areas of low relief quent, and multiple, glacial erosion events. Fortu-

19 Timothy F. Johnsen, Lars Olsen and Andrew Murray

nately in Scandinavia there are many sub-till sites divide to the ice margin, and likely including areas that have already been discovered and that can be in Denmark and southern Sweden, was very dy- studied further to verify the timing and location of namic. These large changes in the ice margin and ice-free periods and to improve our understanding accompanying drawdown of the ice surface would of the dynamic nature of ice sheets (e.g., Roberts- have affected the eastern part of the ice sheet as son and Ambrosiani 1992, Olsen et al. 2001b, well. These conditions have important implications Lundqvist and Robertsson 2002, Lokrantz and for our understanding of ice sheet dynamics and Sohlenius 2006). paleoglaciology, vegetation dynamics, and the relationships between climate change, sea level change, physiography, and Earth rheology. The Conclusion dynamic nature of the SIS allows us to better ac- cept and understand the rapid-paced fluctuations OSL datings of Langsmoen section sub-till sedi- and deglaciation observed at the margins of con- ments from central Norway, using large (8 mm) temporary polar ice sheets, and imagine what is and small (2 mm) aliquots, give consistent ages of possible in the future. 22.3 ±1.7 ka (n = 7). These ages are consistent with radiocarbon datings of sub-till sediments from the nearby Flora section, 21.0 ±1.6 ka (n = 8). The Acknowledgements similarity in age within and between these strati- graphically-related sites and using different geo- We wish to thank Helena Alexanderson of Stock- chronological techniques strongly suggests that this holm University/Norwegian University of Life area was ice-free around ~21 or 22 ka. These posi- Sciences and Jan Lundqvist of Stockholm Univer- tive results show further promise in employing the sity for valuable input into the writing; Jan-Pieter OSL dating technique for dating sub-till ice-distal Buylaert and the technical staff at the Nordic Labo- glaciofluvial/fluvial, as well as other sediments in ratory for Luminescence Dating for helping with Norway. OSL-measurements; Damian Steffen at University We imagine a local paleoenvironment whereby of Bern for introducing Johnsen to the deconvolu- glaciofluvial/fluvial sediments from the tion technique; Irene Lundquist at NGU for techni- Langsmoen site were deposited in ice-distal condi- cal assistance with maps and several drawings; tions, in a narrow fjord with relative sea level at and, field assistants Marie Koitsalu and Jakob 210 m a.s.l. or more, perhaps up to ~220 m a.s.l. Heyman. This project was supported with funding Further advance of the ice sheet leading into LGM from the Swedish Society for Anthropology and 2 resulted in ice damming down-valley from Flora, Geography, Carl Mannerfelts fund, and Ahlmanns ice-margin oscillations and deposition of glacio- fund. lacustrine sediments in ice-proximal conditions, Johnsen was in charge of and performed all as- alternating with till deposition at the Flora sections pects of the project: conception, acquiring funding, with the highest lake level up to at least 310 m OSL-sampling and measurements, data analysis, a.s.l. These sites were in-turn buried by LGM 2 till and writing. Olsen suggested sites for OSL- and glaciotectonized. sampling, guided in the field, provided important Sediments from Langsmoen and Flora sections input to the writing, and completed the original indicate ice-free conditions that are consistent with stratigraphic and sedimentologic fieldwork years other similarly-aged sediments in similar strati- earlier. Murray gave valuable contributions to graphic settings at many other sites in Norway that discussions regarding OSL-preparation and meas- collectively define the Trofors interstadial (~25-20 urement setup, and interpretation of results as well ka; 42 sites and 67 dates); a regional ice-free pe- as provided laboratory access. riod during MIS 2 that is bracketed by LGM 1 and LGM 2 stadials. The existence of the Trofors inter- stadial along with other interstadials during the References Middle and Late Weichselian (MIS 3 and MIS 2) Alexanderson, H., Johnsen, T.F., Murray, A.S., in press. Re- indicates that not only the western margin, but the dating the Pilgrimstad interstadial with OSL: a warmer cli- whole western part of the ice sheet, from the ice

20 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

mate and a smaller ice sheet during the Swedish Middle peratures in northern Scandinavia during the last glaciation. Weichselian (MIS 3)? Boreas. Geology 35, 987-990. Alexanderson, H., Murray, A.S., in press. Problems and poten- Helmens, K.F., Johansson, P.W., Räsänen, M.E., Alexander- tial of OSL dating Weichselian and Holocene sediments in son, H., Eskola, K.O., 2007b. Ice-free intervals at Sokli con- Sweden. Quaternary Science Reviews. tinuing into Marine Isotope Stage 3 in the central area of the Scandinavian glaciations. Geological Society of Finland Alexanderson, H., Eskola, K.O, Helmens, K.F., 2008. Optical Bulletin 79, 17-39. dating of a Late Quaternary sediment sequence from Sokli, northern Finland. Geochronometria 32, 51-59. Hillefors, Å., 1969. Västsveriges glaciala historia och mor- fologi. Naturgeografiska studier. Meddelanden från Lunds Allen, J. R., 1982. Sedimentary structures: their character and Universitets geografiska institution, Avhandlingar 60. 319 p. physical basis, volumes I and II. Developments in Sedimen- tology 30A and 30B, 593 and 663 p. Hillefors, Å., 1974. The stratigraphy and genesis of the Döse- backa and Ellesbo drumlins. A contribution to the knowl- Andersen, B.G., Nydal, R.,Wangen, O.P., Østmo, S.R., 1981. edge of the Weichsel-glacial history in Western Sweden. Weichselian before 15,000 years B.P. at Jaeren-Karmøy in Geologiska Föreningens i Stockholm Förhandlingar 96, southwestern Norway. Boreas 10, 297–314. 355-374. Andersen, B.G., Sejrup, H.P., Kirkhus, Ø., 1983. Eemian and Houmark-Nielsen, M. and Kjær, K.H, 2003. Southwest Scan- Weichselian deposits at Bø on Karmøy, S.W. Norway, a dinavia, 40–15 ka BP: palaeogeography and environmental preliminary report. Norges Geologisk Undersøkelse 380, change. Journal of Quaternary Science 18, 769-786. 189–201. Hubbard, A., Bradwell, T., Golledge, N., Hall, A., Patton, H., Arnold, N.S., van Andel, T.H., Valen, V., 2002. Extent and Sugden, D., Cooper, R., Stoker, M., 2009. Dynamic cycles, Dynamics of the Scandinavian Ice Sheet during Oxygen Iso- ice streams and their impact on the extent, chronology and tope Stage 3 (65,000-25,000 yr B.P.) Quaternary Research deglaciation of the British–Irish ice sheet. Quaternary Sci- 57, 38-48. ence Reviews, 28, 758-776. Banerjee, D., Murray, A. S., Bøtter-Jensen, L., Lang, A., 2001. King, E. L., Sejrup, H. P., Haflidason, H., Elverhøi, A., Equivalent dose estimation using a single aliquot of po- Aarseth, I., 1996. Quaternary seismic stratigraphy of the lymineral fine grains. Radiation Measurements 33, 73-94. North Sea Fan: glacially-fed gravity flow aprons, Bøtter-Jensen, L., Bulur, E., Duller, G.A.T., Murray, A.S., hemipelagic sediments, and large submarine slides. Marine 2000. Advances in luminescence instrument systems. Radia- Geology 130: 293-315. tion Measurements 32, 523-528. Kjær, K.H., Lagerlund, E., Adrielsson, L., Thomas, P., J., Choi, J.H., Duller, G.A.T., Wintle, A.G., 2006. Analysis of Murray, A., Sandgren, P., 2006. The first independent chro- quartz LM-OSL curves. Ancient TL 24, 9-20. nology for Middle and Late Weichselian sediments from southern Sweden and the island of Bornholm. GFF 128, Denton, G.H., Hughes, T.H., 1981. The Last Great Ice Sheets. 209-220. Wiley-Interscience, New York, 484 p. Larsen, E., Gulliksen, S., Lauritzen, S.-E., Lie, R., Løvlie, R., Donner, J., 1995. The Quaternary History of Scandinavia. Mangerud, J., 1987. Cave stratigraphy in western Norway; Cambridge University Press, 206 p. multiple Weichselian glaciations and interstadial vertebrate Duller, G.A.T., 2004. Luminescence dating of Quaternary fauna. Boreas 16, 267-292. sediments: recent advances. Journal of Quaternary Science Lian, O.B., Roberts, R.G., 2006. 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Norges geologiske un- years B.P. based on paired 230Th/234U/238U and 14C dates on dersøkelse, Special Publication, 8, 1-100. pristine corals. Quaternary Science Reviews, 24, 1781-1796. Lundqvist, J., 1992. Glacial stratigraphy of Sweden. Geologi- Fuchs, M., Owen, L.A., 2008. Luminescence dating of glacial cal Survey of Finland, Special Paper 15, 43-59. and associated sediments: review, recommendations and Lundqvist, J., 2004. Glacial history of Sweden. In: Ehlers, J., future directions. Boreas 37, 636-659. Gibbard, P. L.: Quaternary Glaciations – Extent and Chro- Galbraith, R.F., Roberts, R.G., Laslett, G.M., Yoshida, H., nology. Elsevier B. V., p. 401-412. Olley, J.M., 1999. Optical dating of single and multiple Lundqvist, J., and Robertsson, A.-M., 2002. Istider och mel- grains of quartz from Jinmium rock shelter, northern Austra- lanistider. In: Fredén, C. (Ed.) Sveriges Nationalatlas: Berg lia. Part I: experimental design and statistical models. Ar- och jord. 3rd ed. pp. 120-124. chaeometry 41, 339-364. Lunkka, J.P., Murray, A., Korpela, K, 2008. Weichselian Helmens, K.F., Bos, J.A.A., Engels, S., van Meerbeeck, C.J., sediment succession at Ruunaa, Finland, indicating a Mid- Bohncke, S.J.P., Renssen, H., Heiri, O., Brooks, S.J., Seppä, Weichselian ice-free interval in eastern Fennoscandia. Bo- H., Birks, H.J.B., Wohlfarth, B., 2007a. Present-day tem- reas 37, 234-244.

21 Timothy F. Johnsen, Lars Olsen and Andrew Murray

Mangerud, J., 1991. The Scandinavian Ice Sheet through the Olsen, L., Sveian, H. and Bergstrøm, B., 2001a. Rapid adjust- last interglacial/glacial cycle. Paläoklimaforschung, 1, 307- ments of the western part of the Scandinavian ice sheet dur- 330. ing the Mid- and Late Weichselian – a new model. Norges Geologiske Tidsskrift 81, 93-118. Mangerud, J., 2004. Ice-sheet limits on Norway and the Nor- wegian continental shelf. In: Ehlers, J. and Gibbard, P. L. Olsen, L., Sveian, H., Bergstrøm, B., Selvik, S.E, Lauritzen, (Eds.), Quaternary glaciations - extent and chronology. El- S.-E., Stokland, O., Gmsfjeld, K., 2001b. Methods and sevier, Amsterdam, pp. 271-294. stratigraphies used to reconstruct Mid- and Late Weich- selian palaeoenvironmental and palaeoclimatic changes in Mangerud, J., Gulliksen, S., Larsen, E., Longva, O., Miller, Norway. Norges geologiske undersøkelse Bulletin 438, 21- G., Sejrup, H.P., Sønstergaard, E., 1981. A middle Weich- 46. selian ice-free period in western Norway: The Ålesund In- terstadial. Boreas 10, 447–462. Olsen, L., van der Borg, K., Bergstrøm, B., Sveian, H., Lauritzen, S.-E., Hansen, G., 2001c. AMS radiocarbon dat- Mangerud, J., Løvlie, R., Gulliksen, S., Hufthammer, A.-K., ing of glacigenic sediments with low organic carbon con- Larsen, E., Valen, V., 2003. Paleomagnetic correlations be- tent-an important tool for reconstructing the history of gla- tween Scandinavian Ice-Sheet fluctuations and Greenland cial variations in Norway. Norges Geologiske Tidsskrift 81, Dansgaard-Oeschger Events, 45,000-25,000 yr B.P. Quater- 59-92. nary Research 59, 213-222. Olsen, L., Sveian, H., van der Borg, K., Bergstrøm, B., Mangerud, J., Gulliksen, S., Larsen, E., 2010. 14C-dated fluc- Broekmans, M., 2002. Rapid and rhythmic ice sheet fluctua- tuations of the western flank of the Scandinavian Ice Sheet tions in western Scandinavia 15-40 Kya – a review. Polar 45–25 kyr BP compared with Bølling–Younger Dryas fluc- Research 21, 235-242. tuations and Dansgaard–Oeschger events in Greenland. Bo- reas, 39: 328-342. Ottesen, D., Rise, L., Knies, J. Olsen, L., Henriksen, S. 2005. The Vestfjorden-Trænadjupet palaeo-ice stream drainage Middleton, G. V., Hampton, M. A., 1976. Subaqueous sedi- system, mid-Norwegian continental shelf. Marine Geology ment transport and deposition by sediment gravity flows. In: 218, 175- 189. Stanley, D. J., Swift, D. J. P. (Eds.), Marine Sediment Transport and Environmental Management. John Wiley & Prescott, J.R., Hutton, J.T., 1994. Cosmic ray contributions to Sons, New York, pp. 197-218. dose rates for luminescence and ESR dating: large depths and long-term time variations. Radiation Measurements 23, Murray, A.S., Olley, J.M., 2000. Precision and accuracy in the 497-500. optically stimulated luminescence dating of sedimentary quartz: a status review. Geochronometria 21, 1-16. Ramsey, C., 1995. Radiocarbon calibration and analysis of stratigraphy: The OxCal program, Radiocarbon 37, 425-430 Murray, A.S. and Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose Ramsey, C., 2001. Development of the radiocarbon calibration protocol. Radiation Measurements 32, 57-73. program OxCal, Radiocarbon 43, 355-363 Murray, A.S., Wintle, A.G., 2003. The single aliquot regenera- Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, tive dose protocol: potential for improvements in reliability. J.W., Bertrand, C.J.H., Blackwell, P.G., Buck, C.E., Burr, Radiation Measurements 37, 377-381. G.S., Cutler, K.B., Damon, P.E., Edwards, R.L., Fairbanks, R.G., Friedrich, M., Guilderson, T.P., Hogg, A.G., Hughen, Murray, A.S., Marten, R., Johnson, A., Martin, P., 1987. K.A., Kromer, B., McCormac, G., Manning, S., Bronk Analysis for naturally occurring radionuclides at environ- Ramsey, C., Reimer, R.W., Remmele, S., Southon, J.R., mental concentrations by gamma spectrometry. Journal of Stuiver, M., Talamo, S., Taylor, F.W., van der Plicht, J., Radioanalytical and Nuclear Chemistry Articles 115, 263- Weyhenmeyer, C.E., 2004. IntCal04 terrestrial radiocarbon 288. age calibration, 0-26 cal kyr BP. Radiocarbon, 46, 1029- Nygård, A., Sejrup, H.P., Haflidason, H., Bryn, P., 2005. The 1058. glacial North Sea Fan, southern Norwegian Margin: Archi- Robertsson, A.-M., García Ambrosiani, K., 1992. The Pleisto- tecture and evolution from the upper continental slope to the cene in Sweden – a review of research, 1960-1990. Geo- deep-sea basin. Marine and Petroleum Geology, 22, 71-84. logical Survey of Sweden, SGU Ca 81, 299-306. Olsen, L., 1997. 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22 OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet

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23

Dissertations from the Department of Physical Geography and Quaternary Geology No 22

Late Quaternary ice sheet history and dynamics in central and southern Scandinavia Timothy F. Johnsen

Doctoral Thesis in Quaternary Geology at Stockholm University, Sweden 2010 Part of the key to predicting the future behaviour of the Earth is linked to our understanding of how ice sheets have operated in the past. Recent work suggests an emerging new paradigm for the Scan- dinavian ice sheet (SIS); one of a dynamically fluctuating ice sheet. This doctoral research project explicitly examines the history and dynamics of the SIS at four sites within Sweden and Norway, and provides results covering different time periods of glacial history. Two relatively new dating techniques are used to constrain the ice sheet history.

Dating of sub-till sediments in central Sweden and central Norway indicate ice-free conditions during times when it was previously inferred the sites were occupied by the SIS. Consistent exposure ages of boulders from the Vimmerby moraine in southern Sweden indicate that the southern margin of the SIS was at the Vimmerby moraine ~14 kyr ago. In central Sweden, consistent exposure ages for boulders at high elevation agree with previous estimates for the timing of deglaciation around 10 ka ago, and indicate rapid thinning of the SIS during deglaciation.

Altogether this research conducted in different areas, covering dif- ferent time periods, and using comparative geochronological met- hods demonstrates that the SIS was highly dynamic and sensitive to environmental change.

I was born and raised on Vancouver Island on the west coast of Canada surrounded by beautiful mountains and coastline, where I developed a deep curiosity and passion for understanding the workings of nature. I completed a Bachelor of Science degree with distinction in Geography 1998 at the University of Victoria, Canada. Then I completed a Masters of Science degree in Geography 2004 at Simon Fraser University, Canada, for which I was awarded the Canadian Association of Geographers Starkey-Robinson Award 2005. I began a PhD in 2004 in Stockholm, Sweden investigating the dynamics of the Scandinavian ice sheet, and eating brown cheese with waffles under the midnight sun.

ISBN 978-91-7447-068-0 ISSN 1653-7211

Department of Physical Geography and Quaternary Geology