# Weichselian–Holocene glacial history of the Sjuøyane archipelago, northern Svalbard

Anders Schomacker, Helena Alexanderson, Wr Farnsworth, Mark Furze, Sofia

Kjellman, Nina Kirchner, Elias Strandell Erstorp, Riko Noormets, Vincent

Jomelli, Ólafur Ingólfsson

► To cite this version:

Anders Schomacker, Helena Alexanderson, Wr Farnsworth, Mark Furze, Sofia Kjellman, et al. Weichselian–Holocene glacial history of the Sjuøyane archipelago, northern Svalbard. Boreas, 2024, 10.1111/bor.12673. hal-04737794

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# Weichselian–Holocene glacial history of the Sjuøyane archipelago, northern Svalbard

ANDERS SCHOMACKER (1), HELENA ALEXANDERSON, WESLEY R. FARNSWORTH (2), MARK F. A. FURZE, SOFIA E. KJELLMAN (3), NINA KIRCHNER, ELIAS STRANDELL ERSTORP, RIKO NOORMETS, VINCENT JOMELLI AND ÓLAFUR INGÓLFSSON

BOREAS

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Schomacker, A., Alexanderson, H., Farnsworth, W. R., Furze, M. F. A., Kjellman, S. E., Kirchner, N., Erstorp, E. S., Noormets, R., Jomelli, V. & Ingólfsson, Ó.: Weichselian–Holocene glacial history of the Sjuøyane archipelago, northern Svalbard. *Boreas*. https://doi.org/10.1111/bor.12673. ISSN 0300-9483.

The Sjuøyane archipelago is the northernmost land area of Svalbard; thus, it provides a window to study the terrestrial glacial history and dynamics of the Svalbard–Barents Sea Ice Sheet and complement marine geological studies in the region. To reconstruct the glacial history of Sjuøyane, we describe coastal sedimentary sections in Quaternary sediments and constrain their chronology by radiocarbon and optically stimulated luminescence ages. Erratic boulders and bedrock are sampled for $^{10}$Be cosmogenic exposure dating, aiming to determine the deglaciation age and exposure history. Holocene environments are studied based on lake sediments and emerging vegetation from retreating snow patches. The sedimentary sections largely consist of shallow (glacio-)marine and/or littoral sediments deposited during high relative sea levels. The radiocarbon and luminescence ages suggest they formed during a Middle Weichselian interstadial, and after the Late Weichselian glaciation. A wave-washed bedrock erosional notch and rounded boulders at 36±1 m a.h.t. most likely formed during this interstadial. Most of the cosmogenic $^{10}$Be ages are older than the last deglaciation, likely indicating a complex exposure history. One boulder sample suggests that the lowlands were deglaciated 14.7±1.82 ka ago, and two boulder samples with ages of 18.94±3.26 and 22.89±4.05 ka suggest that the highlands were possibly ice-free at this time. The lake sediments from Isvatnet, Phippsøya, consist of glaciolacustrine silt and clay overlain by gyttja. The gyttja has accumulated at least since 7.0 cal. ka BP. Two radiocarbon ages from emerging vegetation suggest Neoglacial cooling since 3.8 cal. ka BP. A patchy glacial drift at the surface of Sjuøyane and well-preserved pre-Late Weichselian sediments suggest that the Late Weichselian glaciation was non-erosive and/or cold-based at this part of the north margin of the Svalbard–Barents Sea Ice Sheet.

Anders Schomacker (anders.schomacker@uit.no) and Sofia E. Kjellman, Department of Geosciences,UiT The Arctic University of Norway, Postboks 6050 Langnes, NO-9037 Tromsø, Norway; Helena Alexanderson, Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden; Wesley R. Farnsworth, Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, IS-102 Reykjavik, Iceland and Globe Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark and Nordic Volcanological Center, University of Iceland, Askja, Sturlugata 7, IS-102 Reykjavik, Iceland; Mark F. A. Furze and Riko Noormets, Department of Arctic Geology, The University Centre in Svalbard (UNIS), P.O. Box 156, NO-9171 Longyearbyen, Norway; Nina Kirchner, Department of Physical Geography, Stockholm University, SE-106 91 Stockholm, Sweden; Elias Strandell Erstorp, Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden; Vincent Jomelli, Aix Marseille University, CNRS, IRD, INRAE, CEREGE, BP 80, F-13545 Aix-en-Provence Cedex 4, France; Ólafur Ingólfsson, Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, IS-102 Reykjavik, Iceland; received 13th February 2024, accepted 8th July 2024.

Marine geological data from the continental shelf north of Svalbard suggest that the Svalbard–Barents Sea Ice Sheet (SBIS) was at its Local Last Glacial Maximum (LLGM) c. 26 cal. ka BP, close to the continental shelf break north of Sjuøyane, northernmost Svalbard (e.g. Kleiber et al. 2000; Knies et al. 2001; Svendsen et al. 2004; Chauhan et al. 2014, 2016; Patton et al. 2015; Fig. 1). Mega-scale glacial lineations at the sea floor indicate LLGM ice-stream activity in the Hinlopen Trough (Ottesen et al. 2007; Dowdeswell et al. 2010; Batchelor et al. 2011), and subglacially elongated landforms in the Kvitøya Trough suggest that a major warm-based outlet glacier occupied this trough (Hogan et al. 2010). Fransner et al. (2017) mapped subglacially streamlined landforms in Duvefjorden and Rijpfjorden, northern Nordaustlandet, suggesting topographically controlled, rapid ice flow occurred in these fjords. The continental shelf north of Svalbard

between these troughs is up to ~200 m deep (Jakobsson et al. 2020), and was characterized by less active, thin and possibly cold-based, glacier flow during the LLGM (Hogan et al. 2010). Such a LLGM configuration with fast ice flow in the troughs and less active, possibly cold-based, ice on the continental shelf is supported by numerical ice-sheet models (e.g. Patton et al. 2016) and conceptual glaciation models (e.g. Landvik et al. 1998, 2005; Ingólfsson 2011; Ingólfsson & Landvik 2013). A radiocarbon age of mixed benthic foraminifera in deglacial glaciomarine sediment, 6 cm above a diamicton in core JR142-GC13 from the upper continental slope ~65 km north of Sjuøyane provides a minimum age of 15.3 cal. ka BP for the retreat of grounded ice (Lab. no SUERC-47932; Hogan et al. 2017; Fig. 1, Table S1). To the east of Sjuøyane, a radiocarbon age from sediment core HH15-14 on the continental shelf suggests that the shelf west of the Albertini Trough was
<figure><img src="image_4.png" /><figcaption>Fig. 1. A. Map of Svalbard with place names mentioned in the text. The dashed line marks the extent of the Svalbard–Barents Sea Ice Sheet during the Last Glacial Maximum (LGM) after Ingólfsson & Landvik (2013). Background map modified from Norwegian Polar Institute (2017). B. Map of the Sjuøyane archipelago with sample sites and place names mentioned in the text indicated. The terrain shaded relief model is based on a 20-m digital elevation model produced by stereophotogrammetry on aerial photographs from 2010 by the Norwegian Polar Institute (2014). The elevation contour lines are shown with 50-m intervals. C. Location of Svalbard in the Arctic.</figcaption></figure>

ice-free by 15.2 cal. ka BP (Fransner et al. 2018; Fig. 1, Table S1).

Compared to other parts of the archipelago, few terrestrial Quaternary stratigraphical sections have been described from northeastern Svalbard. On Brageneset, Nordaustlandet, Donner & West (1957) identified till with fabrics indicating ice flow towards the southwest into the Hinlopen Strait. Further north on Nordaustlandet, in Murchinsonfjorden, Kaakinen et al. (2009) described the Quaternary lithostratigraphy in Isvika (Fig. 1) and determined the ages of shallow marine sediments using radiocarbon dating and OSL dating. They identified three subglacial till beds with fabrics showing westerly ice-flow directions towards the Hinlopen Strait. This is supported by the orientation of striae on bedrock outcrops in the area. Each till bed is stratigraphically overlain by shallow marine sand and gravel. The OSL ages of the shallow marine sediments are 83.1±10.2 ka (Early Weichselian interstadial, MIS 5a), 37.0±3.7 ka (Middle Weichselian interstadial, MIS 3), and Holocene. The Middle Weichselian OSL age overlaps within the 2σ age range of 52.0–40.0 cal. ka BP (Lab. no. HELA-1653; Table S1) of radiocarbon-dated shell fragments in the same unit. The preservation of older sediments, weathered bedrock, and restricted lateral distribution of the sediments suggest that the glaciers that deposited the till beds were mainly cold-based and located east of the ice stream in the Hinlopen Strait (Kaakinen et al. 2009). Hormes et al. (2011) used cosmogenic exposure dating of 19 bedrock and erratic boulder samples in the Murchinsonfjorden area and Prins Oscars Land area on Nordaustlandet to constrain

the timing of deglaciation. The ages range from 122.8±7.6 to 13.0±2.2 ka ago. The youngest dates (15.4–13.0 ka ago) provide deglaciation ages of the lowlands and fjords, and together with geomorphological evidence of subglacial erosion suggest that the glaciers were warm-based in the topographic lows. In contrast, none of the bedrock and boulder samples from the uplands and plateaux yielded ages from the last deglaciation. Seven of these have MIS 3 ages, and the remaining are older. These ages probably indicate a complex exposure history and inherited isotopes in the samples. Based on these ages and glacial geological mapping, Hormes et al. (2011) concluded that the higher elevation parts (>~200 m a.s.l.) of Nordaustlandet were covered by cold-based ice in MIS 2, and that uplands in Prins Oscars Land might not have been glaciated since MIS 4. The large-scale spatial pattern of postglacial glacio-isostatic rebound reconstructed from raised beaches on Svalbard shows a decreasing ice load towards the north on Nordaustlandet and Sjuøyane (e.g. Blake 1961; Bondevik 1993; Forman & Ingólfsson 2000; Forman et al. 2004; Schomacker et al. 2019). Forman et al. (2004) proposed a 2–6 ka duration of LLGM glacier ice cover along the north margin of the SBIS, north of Sjuøyane.

The Sjuøyane archipelago, north of Nordaustlandet is the northernmost land area of Svalbard, and a key – yet understudied – site to reconstruct the glacial history and dynamics of the northern margin of the Weichselian SBIS. This paper aims to reconstruct the Weichselian and Holocene glaciation history of Sjuøyane using lithostratigraphy and geochronology of sedimentary sections
and lake sediments as well as cosmogenic exposure dating of bedrock and boulders to constrain the timing of the deglaciation. Further, we discuss our results in the context of previous marine and terrestrial studies in the area. Our terrestrial data provide new insight into the geomorphology, lithology, lateral distribution, and chronology of the Quaternary deposits on Sjuøyane. Thus, they complement earlier marine sediment studies, which mainly focus on the timing of deglaciation and palaeoceanography of the region.

## Background

### Setting

Sjuøyane is an archipelago (latitude ~80.7°N, longitude 20.9°E) north of Nordaustlandet, northeastern Svalbard (Fig. 1). A ~30-km-wide strait separates Sjuøyane from Nordaustlandet, and the continental shelf between Sjuøyane and Nordaustlandet is ~50–100 m deep (Jakobsson et al. 2020). To the north, the archipelago is exposed towards the Arctic Ocean. The bedrock is mainly migmatites of the Mesoproterozoic Duvefjorden Complex and Caledonian granites of the Rijpfjorden Granitoid Suite (Dallmann 2015). The islands are glacially sculpted and consist of individual mountain summits up to 464 m a.s.l. The summits on each island are connected by lowlands of raised beach ridge plains, glacial drift, talus, and locally weathered bedrock (Fig. 2). The largest lake in the archipelago, Isvatnet, is located 33 m a.s.l. in the lowlands between mountains Høgberget and Trollenykjen, Phippsøya (Figs 1B, 2B).

### Glaciation history

Forman & Ingólfsson (2000) described gentle south-facing mountain slopes and steep north-facing slopes on Phippsøya, indicating glacial overriding from a southerly direction during Quaternary glaciations. This interpretation is supported by erratic boulders of granite with a provenance from Nordaustlandet occurring on Sjuøyane (Salvigsen & Nydal 1981; Forman & Ingólfsson 2000). A patchy glacial drift occurs on Sjuøyane above the postglacial marine limit. It contains marine shell fragments suggesting that glaciers eroded the surrounding shelf before depositing the drift. Two median radiocarbon ages of 42.7 (Lab. no. GX-22385-AMS) and 42.0 cal. ka BP (Lab. no. T-3102) from shell fragments in the drift provide its maximum age (Salvigsen & Nydal 1981; Forman & Ingólfsson 2000; Table S1). Few stratigraphical sections are available along the coasts of the islands, e.g. at the southern part of Phippsøya. Forman & Ingólfsson (2000) described a 4-m-high section on Phippsøya, and identified shallow marine sands deposited during high relative sea level. A radiocarbon age of a *Hiatella arctica* shell in the sands yields a median age of 50.5 cal. ka BP (Lab. no.

GX-22388; Forman & Ingólfsson 2000; Table S1). The postglacial marine limit on Phippsøya is located at 22±1 m above high tide (a.h.t.) and raised beaches indicate glacio-isostatic rebound following the Late Weichselian glaciation (Salvigsen & Nydal 1981; Forman & Ingólfsson 2000). The age of the postglacial marine limit is not well defined but is constrained by a minimum age of 10.6 cal. ka BP of a *Balanus balanus* at 10 m a.h.t. (Lab. no. GG-22386; Forman & Ingólfsson 2000; Table S1). There are currently no glaciers on Sjuøyane, but perennial snow patches persist, and in some cases are located just above sea level. Leirdal (1997) estimated an ice-marginal position 15–20 km north of Sjuøyane during the Late Weichselian.

## Material and methods

### Bathymetry and lake sediment coring

The bathymetry of Isvatnet, Phippsøya (80.70°N, 20.96°E, 33 m a.s.l.; Fig. 1B) was surveyed in August 2018 with an autonomous surface vehicle (ASV) developed as part of a fleet of maritime robots at the Department of Naval Architecture at KTH Royal Institute of Technology, Stockholm. The ASV's standard payload comprises a GPS receiver, motion sensor, and an EchoRange Smart SS510 single beam echo-sounder for bathymetric mapping of shallow waters, which it carries out on a predefined, mission-specific horizontal grid with a user-defined and application-specific mesh cell size. Given the ASV's typical speed of 1.75 kn (~0.9 m s⁻¹), and the 1-Hz transmit frequency of the echo-sounder, the resolution of the bathymetric data acquired here is on the order of 1 sounding per metre along path, and 1 sounding per 10–20 m across path. The acquired geophysical soundings are transformed from time to depth using a sound velocity of 1426 m s⁻¹ for freshwater at 5 °C. For further details, see Kirchner et al. (2019) and Vacek et al. (in press).

Two short sediment cores were retrieved from the deepest part of the lake basin. The coring was performed through a hole in the floor of a zodiac, which was anchored at a stable position. A Universal percussion sediment corer from Aquatic Research Instruments was used to obtain a 38-cm-long core (IVS2) and a 34-cm-long core (IVS3), both with 68-mm diameter.

### Sedimentological analyses

Lake sediment cores were split open, lithostratigraphically logged, and photographed with a RGB line scan camera mounted on an Aavatech core scanner. X-ray imagery was recorded using a Geotek Standard X-ray CT System (XCT). Samples for radiocarbon dating were collected from core IVS3.
<figure><img src="image_5.png" /><figcaption>Fig. 2. Geomorphology of Sjuøyane. A. View towards the southwest across Isflakbukta. Hytteberget and Granittberget are seen in the background. 2nd August 2016. B. Isvatnet seen towards the north. Note the zodiac (circled) on the lake for scale. 2nd August 2016. C. View towards the west of the perennial snow patch at Øykollen, Parryøya. Sample positions are marked with arrows. The circle shows persons for scale. 4th August 2016. D. Erosional bedrock notch (arrow) at the foot of Hytteberget in Isflakbukta, Phippsøya, 21st August 2018. The bedrock notch is oriented in the view direction of the photograph, and the two persons are standing on it.</figcaption></figure>

Coastal sedimentary sections were excavated and described in the field by logging, documentation of lithofacies, sediment texture and structure, directional elements, and fossils (e.g. Eyles *et al.* 1983; Evans & Benn 2004). Samples for OSL dating and radiocarbon dating were collected from these sections.

## Radiocarbon dating

To establish the chronology of the lake sediment cores and geological sections, plant macrofossils and marine bivalve shells were collected. Additionally, two samples of *in situ* moss emerging at the margin of a ~200-m-long, perennial snow patch in the mountain slope in southwest Sandvika, Parryøya (Fig. 1B), were collected. These samples were collected at 260 and 57 m a.s.l., respectively. Plant macrofossil samples from lake sediment core IVS3 were taken from the residues of 0.25-mm sieving, isolated, and described using a binocular microscope. All samples were accelerator mass spectrometry (AMS) radiocarbon dated at the Ångström Laboratory, Uppsala University. The ages were calibrated in OxCAL v4.4. using the IntCal20 and Marine20 calibration curves for terrestrial and marine samples, respectively (Heaton

*et al.* 2020; Reimer *et al.* 2020). For marine ages, we applied a ΔRvalue of −61±37 years, calculated for shells from western Svalbard (Piénkowski *et al.* 2022). The relationship between depth and age of the lake sediment cores was established with the Bayesian-based code ‘Bacon’ (v.2.5.7; Blaauw & Christen 2011) in R (v.4.1.3; R Core Team 2021). All reported ages are in calibrated years before present (‘cal. a BP’; BP = AD 1950).

## Luminescence dating

Nineteen samples for luminescence dating were taken in opaque tubes that were hammered horizontally into exposed sediment faces, specifically sandy beds, on Phippsøya and Parryøya (Fig. 1). The samples were opened and analysed in the Lund Luminescence Laboratory, Lund University, Sweden. Details of the analytical procedure are presented in Data S1 and Figs S1–S4, and only a short description is given here. The equivalent dose (*D*<sub>e</sub>) was determined from 2-mm aliquots of 180–250 µm K-feldspar grains by applying a post-IR<sub>50</sub> IRSL<sub>225</sub> (pIRIR) single aliquot regeneration (SAR) protocol according to Buylaert *et al.* (2009) in Risø TL/OSL readers model DA-20. For one sample
(16029), 1-mm aliquots were also used. The suitability of the protocol for these samples was tested in dose recovery experiments, and fading rates and residual doses were also determined (Data S1). Between 8 and 36 aliquots were measured for Dₑ for each sample and they were accepted if they had a recycling ratio within 10% of unity, a test dose error <10% and recuperation <5% of the natural signal. The mean Dₑ of the accepted aliquots for each sample was used for age calculation.

Sediment dose rates were determined by gamma spectrometry at the Nordic Laboratory for Luminescence Dating/DTU Risø, Denmark. An internal K-content of 12.5% was assumed (Huntley & Baril 1997). Subsamples were weighed in their natural state, when saturated and when dry to determine field and saturated water content. The average water content since time of deposition is assumed to be close to saturation (based on at least partly permafrozen coastal setting or covered by ice sheet). The total environmental dose rate (Table S2) and the age for each sample were calculated in the online DRAC v.1.2 calculator (Durcan et al. 2015). Fading-corrected ages were calculated according to Huntley & Lamothe (2001) and using the function calc_FadingCorr in the R Luminescence package (Kreutzer 2018).

## Cosmogenic nuclide dating

Nine samples were collected from Martensøya, Parryøya, and Phippsøya (Fig. 1B). We sampled bedrock and boulders on high terrain surfaces or small bedrock knobs. All samples are above the marine limit. To minimize the risk of inherited isotopes from previous exposures, we targeted erratic boulders, assuming that they had not been previously exposed to cosmic radiation (Briner et al. 2006; Corbett et al. 2013). However, suitable boulders (i.e. large, stably lodged, not weathered) are very few, and we therefore also sampled bedrock. If glacial erosion of the bedrock surface was insufficient to remove inherited isotopes, this might result in overestimated exposure ages (e.g. Gjermundsen et al. 2015). It is unlikely that any snow, sediment or vegetation has covered the sample sites, since they are located at small summits where wind prevents snow accumulation during winters. There is no field evidence of a sediment cover at or near the sampling sites. The topographic shielding was measured in the field with a compass and clinometer, and correction values calculated according to Balco et al. (2008).

Samples were crushed and sieved at UiT The Arctic University of Norway, and subsequently processed for ¹⁰Be extraction at LN2C (CEREGE, France) following chemical procedures adapted from Merchel & Herpers (1999). The ¹⁰Be/⁹Be ratio measurements were performed at the ASTER AMS national facility (CEREGE, Aix-en-Provence). Samples were calibrated against the in-house standard STD-11

(¹⁰Be/⁹Be = 1.191±0.013 × 10⁻¹¹; Braucher et al. 2015) and a ¹⁰Be half-life of 1.387±0.0012 × 10⁶ years (Chmeleff et al. 2010; Korschinek et al. 2010). All ¹⁰Be/⁹Be isotope ratios are reported following the 07KNSTD standardization (Nishiizumi et al. 2007), and ¹⁰Be ages were calculated using the CREp online calculator (Martin et al. 2017) with a time-invariant scaling scheme for spallation (Lal 1991; Stone 2000), assuming no denudation and the Arctic production rate of 3.96±0.15 atoms g⁻¹ year⁻¹ (Young et al. 2013). We decided to use the Lal/Stone scaling scheme for spallation since the influence of the Earth's magnetic field on the ¹⁰Be production rate is negligible at the high latitude of Sjuøyane (~80°N; Gosse & Phillips 2001). The Arctic production rate (Young et al. 2013) was applied because it is generated from and tested against independent chronologies in comparable settings to Sjuøyane (i.e. high northern latitudes and low altitudes). We report individual ages with their associated uncertainties that include the standard deviations of both analytical ('internal') and production rate ('external') uncertainties when comparing to other studies or ages.

## Results and interpretation

### The lake sedimentary record, Isvatnet, Phippsøya

The bathymetric survey of Isvatnet showed that the lake has two bowl-shaped sub-basins (Fig. 3C). The south-eastern basin reaches a water depth of ~6.5 m, and the northwestern basin reaches ~12 m water depth. Sediment cores IVS2 (38 cm long) and IVS3 (34 cm long) were obtained from the floor of the deeper, northwestern basin at a water depth of ~11 m.

We identified two main sedimentary facies in the sediment cores: dark to light grey silty clay and clayey silt, and olive-brown laminated gyttja (Fig. 3A). We focus on core IVS3, which is the core we radiocarbon dated (Table 1, Fig. 3). The lowermost lithological unit (LU 1) can be subdivided into LU 1a (34–21 cm) and LU 1b (21–15 cm). LU 1a consists of structureless massive dark grey to grey silty clay with an outsized clast in the bottom preventing us from penetrating further. LU 1b consists of light grey clayey silt and appears structureless to the naked eye, but the X-ray reveals tilted layers. LU 1 is lacking age constraints due to the absence of dateable material, but interpreted to represent glaciolacustrine sedimentation. The contact between LU 1 and the overlying unit LU 2 (15–0 cm) is sharp. We interpret this to reflect a hiatus due to a period of nondeposition and/or erosion of underlying sediments. The contact was sharp in both IVS2 and IVS3. The uppermost 15 cm of IVS3 consists of 2–6 mm thick laminae of gyttja with high content of aquatic bryophytes. The lowermost ¹⁴C date in LU 2 (14–15 cm; Lab. no. Ua-71538) has a calibrated median age of 7.0 cal. ka BP (Table 1), and the age-depth model suggests continuous organic accumulation
<figure><img src="image_6.png" /><figcaption>Fig. 3. A. Core photograph, X-ray image, sedimentological log, and calibrated radiocarbon ages for lake sediment core IVS3 from Isvatnet, Phippsøya. B. Age-depth model for the upper part of the core (lithological unit 2). Details on the radiocarbon ages are given in Table 1. C. Bathymetry of Isvatnet, with the coring location indicated.</figcaption></figure>

through the rest of the Holocene (Fig. 3B). There is no sedimentological evidence of Neoglacial cooling.

### Radiocarbon ages of moss emerging from snow patch in Sandvika, Parryøya

Sample 7ISL-2016-B30 (Lab. no. Ua-54605; 260 m a.s.l.) has a median age of 3.8 cal. ka BP and sample 7ISL-2016-B26 (Lab. no. Ua-54604; 57 m a.s.l.) has a median age of 2.8 cal. ka BP (Table 1). We interpret these ages as indicating that the snow patch was expanding at this time, thereby killing the moss growing at the surface (Fig. 2C).

### Lithostratigraphy of coastal sections

Five sedimentary sections were studied on Phippsøya and three on Parryøya. On Phippsøya, coastal sections were investigated in Isflakbukta, Trollodden, Horgvika, Utkiksnosa, and Eidsbukta (Fig. 1B). In Sandvika, Parryøya, small streams fed by snow meltwater have eroded sections into landforms with a near-horizontal surface. They occur below the marine limit, ~200 m from the present coastline (Fig. 1B). We identified four lithofacies associations (LA) in the sections based on their appearance in the field (architecture, boundaries, texture, structures, and fossil content; Figs 4, 5).

LA 1 is a massive, matrix-supported silty-sandy diamict. It is observed at the base of the sections Isflakbukta 1 and Horgvika, where it transitions into permafrost. Therefore, no basal contacts are visible. In

Isflakbukta, the matrix of the diamict shows normal grading. At Horgvika, paired shells, whole shells, and shell fragments of bivalves occur in the diamict. The clasts are of varied lithology. Further, LA 1 consists of a bi-modal sediment of boulders and massive sand with shell fragments observed at Horgvika. The Horgvika site (Fig. 4A) was also described by Salvigsen & Nydal (1981) and Forman & Ingólfsson (2000).

LA 1 has not been sufficiently investigated to allow a detailed genetic interpretation of the diamict (e.g. Eyles et al. 1983; Krüger & Kjær 1999; Benn & Evans 2010). The diamict might be deposited in a glacial or glaciomarine environment, and the bivalve shells and shell fragments suggest that the sediment originates from shallow marine or littoral deposits. The boulders in the bi-modal sediment in the upper part of LA 1 at Horgvika could have originated as rockfall material from the slopes above the sections entering a shallow marine or littoral setting (in agreement with Forman & Ingólfsson 2000).

LA 2 consists of beds of sand, gravelly sand, and silty sand (Figs 4, 5). Occasional beds of slightly coarser (i.e. gravel) and finer (i.e. silt) sediment occur. In Eidsbukta the upper part of LA 2 consists of beds of sandy-gravelly bi-modal sediment. Each bed is 5–65 cm thick. Most of the sand and gravelly sand beds are massive, although ripple-laminated sand and laminated sand are present in the Isflakbukta 2 and Trollodden 2 sections. Paired shells, whole shells, and shell fragments of bivalves (mainly *Mya truncata*) are observed frequently in LA 2. The LA has a lateral extent of 200–300 m at Isflakbukta and Trollodden. LA 2 also appears in three sections (Sandvika 1–3) in
<table><caption>Table 1. Radiocarbon ages from Sjuøyane, Svalbard, calibrated in OxCal v4.4. with IntCal20 (Reimer et al. 2020) or Marine20 (Heaton et al. 2020) and a ΔR value of −61±37 years for shells (Pienkowski et al. 2022).</caption><thead><tr><th>Sample</th><th>Location</th><th>Latitude and longitude (decimal degree)</th><th>Material dated</th><th>Lab. ID</th><th>Elevation (m a.s.l.) or Core depth (midpoint; cm)</th><th><sup>14</sup>C age (a BP)</th><th>Calibrated median age (cal. a BP)</th><th>Calibrated 2σ age ranges (cal. a BP)</th><th>δ<sup>13</sup>C (‰ VPDB)</th></tr></thead><tbody><tr><td colspan="10"><strong>Phippsøya</strong></td></tr><tr><td>7ISL-2016-A-06</td><td>Utkiksnosa</td><td>80.6844°N, 20.8623°E</td><td>Paired bivalve shell</td><td>Ua-54598</td><td>7</td><td>>40 000</td><td>—</td><td>—</td><td>+2.1</td></tr><tr><td>7ISL-2016-D-1</td><td>Isflakbukta 1</td><td>80.6953°N, 20.9368°E</td><td>Shell in living position</td><td>Ua-54600</td><td>3.2</td><td>9621±41</td><td>10 412</td><td>10 626–10 216</td><td>+1.5</td></tr><tr><td>IVS3_1_2</td><td>Isvatnet</td><td>80.7000°N, 20.9600°E</td><td>Aquatic bryophytes</td><td>Ua-71532</td><td>1.5</td><td>2063±29</td><td>2022</td><td>2112–1939</td><td>-30.1</td></tr><tr><td>IVS3_3_4</td><td>Isvatnet</td><td>80.7000°N, 20.9600°E</td><td>Aquatic bryophytes</td><td>Ua-71533</td><td>3.5</td><td>2292±34</td><td>2315</td><td>2355–2300, 2251–2157</td><td>N/A</td></tr><tr><td>IVS3_5_6</td><td>Isvatnet</td><td>80.7000°N, 20.9600°E</td><td>Aquatic bryophytes</td><td>Ua-71534</td><td>5.5</td><td>2699±30</td><td>2800</td><td>2854–2755</td><td>-23.0</td></tr><tr><td>IVS3_7_8</td><td>Isvatnet</td><td>80.7000°N, 20.9600°E</td><td>Aquatic bryophytes</td><td>Ua-71535</td><td>7.5</td><td>3126±43</td><td>3345</td><td>3447–3231</td><td>N/A</td></tr><tr><td>IVS3_10_11</td><td>Isvatnet</td><td>80.7000°N, 20.9600°E</td><td>Aquatic bryophytes</td><td>Ua-71536</td><td>10.5</td><td>3644±37</td><td>3961</td><td>4086–3871, 3859–3850</td><td>N/A</td></tr><tr><td>IVS3_12_13</td><td>Isvatnet</td><td>80.7000°N, 20.9600°E</td><td>Aquatic bryophytes</td><td>Ua-71537</td><td>12.5</td><td>6201±33</td><td>7083</td><td>7245–7210, 7170–6992</td><td>-20.4</td></tr><tr><td>IVS3_14_15</td><td>Isvatnet</td><td>80.7000°N, 20.9600°E</td><td>Aquatic bryophytes</td><td>Ua-71538</td><td>14.5</td><td>6136±42</td><td>7030</td><td>7160–6901</td><td>N/A</td></tr><tr><td colspan="10"><strong>Parryøya</strong></td></tr><tr><td>7ISL-2016-C-9</td><td>Sandvika 2</td><td>80.6485°N, 20.6400°E</td><td>Paired <i>Mya truncata</i></td><td>Ua-54599</td><td>7</td><td>9819±43</td><td>10 700</td><td>11 001–10 482</td><td>+2.9</td></tr><tr><td>7ISL-2016-B-26</td><td>Sandvika</td><td>80.6479°N, 20.6211°E</td><td>Moss</td><td>Ua-54604</td><td>57</td><td>2649±33</td><td>2761</td><td>2848–2814, 2791–2728</td><td>-25.9</td></tr><tr><td>7ISL-2016-B-30</td><td>Sandvika</td><td>80.6442°N, 20.6038°E</td><td>Moss</td><td>Ua-54605</td><td>260</td><td>3551±33</td><td>3844</td><td>3965–3947, 3927–3816, 3800–3719</td><td>-23.6</td></tr></tbody></table>

Sandvika, Parryøya (Figs 1B, 5), and consists of massive or planar-bedded gravel and sand. The Sandvika 1 section comprises a 2-m-thick coarsening-upward succession of mainly planar beds, each 10–40 cm thick and dipping towards the north. Sandvika 2 contains paired *Mya truncata* shells.

We interpret LA 2 as deposited in shallow (glacio-) marine or littoral environments. The gravel, gravelly sand, and sand beds are deposited in beach-face and/or shore-face environments, and the fines and ripple-laminated and laminated sand beds in a shallow marine environment (Mangerud et al. 1998; Alexander-son et al. 2011). The ripple-laminated sand indicates deposition in shallow marine conditions affected by waves and/or strong bottom currents (e.g. Ó Cofaigh & Dowdeswell 2001). In Sandvika, LA 2 possibly represents foreset beds in a delta prograding towards the north, and deposited during regression (e.g. Mangerud et al. 1998; Alexander-son et al. 2011).

LA 3 is a massive, matrix-supported sandy-gravelly diamict. It occurs in the Utkiksnosa and Isflakbukta 1 sections where it is 1–2 m thick. Large clasts appear subrounded and are of local lithology. One clast with attached barnacle fragments (*Balanus* sp.) was observed.

The massive appearance and the subrounded clasts suggest that LA 3 is deposited in a glacial environment, although the diamict has not been sufficiently investigated to allow a detailed genetic interpretation (e.g. Eyles et al. 1983; Krüger & Kjær 1999; Benn & Evans 2010). The barnacle fragments suggest that the clasts are reworked from shallow marine or littoral deposits.

LA 4 consists of gravelly sand, gravel, cobbles, and boulders and is 25 cm to more than 160 cm thick (Fig. 4). The beds are massive, and there is a coarsening-upwards trend in grain size. At Isflakbukta 2 and Trollodden 2, normal graded, cross-planar beds of rounded cobbles and boulders dip gently offshore from each site (towards the northwest and northeast, respectively; Fig. 4D, E). The lithofacies association can be followed laterally for ~300 m in Isflakbukta and Trollodden and has an erosive or conformal basal contact.

We interpret LA 4 as prograding beach-face sediments deposited during regression. The relatively poor sorting suggests a large sediment input and/or rapid sedimentation (Bluck 1999; Strzelecki et al. 2018). The northwest-dipping beds in Isflakbukta and the northeast-dipping beds at Trollodden indicate that the sediments were
<figure><img src="image_7.png" /><figcaption>Fig. 4. A–G. Sedimentological logs from the sections on Phippsøya. The locations of the sections are shown in Fig. 1B. Details on radiocarbon ages (italics) and OSL ages are provided in Tables 1, 2. H. Overview map of Phippsøya with the locations of the sections.</figcaption></figure>

building into the bays during deposition (e.g. Mangerud *et al.* 1998; Alexanderson *et al.* 2011).

The sections in Sandvika, Isflakbukta, Trollodden, and Eidsbukta reveal clear shallowing-upward successions of (glacio-)marine deposits (Figs 4, 5), which we interpret as indicating sedimentation during regression caused by glacio-isostatic rebound (e.g. Mangerud *et al.* 1998; Alexanderson *et al.* 2011). The sections at Utkiksnosa and Isflakbukta 2 possibly reflect two such successions.

## Radiocarbon and luminescence ages from the sedimentary sections

Two radiocarbon ages were obtained from the sections on Phippsøya, yielding an age of >40 cal. ka BP for LA 2

(Fig. 4B, Table 1; Lab. no. Ua-54598), and a median age of 10.4 cal. ka BP for LA 3 (Fig. 4B, Table 1; Lab. no. Ua-54600), respectively. Additionally, one radiocarbon age was obtained from LA 2 on Parryøya, yielding a median age of 10.7 cal. ka BP (Fig. 5B, Table 1; Lab. no. Ua-54599).

We prefer using the pIRIR ages, since they are generally considered more stable than IR$_{50}$ ages, which fade and, hence, underestimate the age (Buylaert *et al.* 2009; Table 2, Figs 4, 5). However, the pIRIR signal bleaches more slowly than the IR$_{50}$ (and OSL) signal and therefore runs a greater risk of suffering from incomplete bleaching and age overestimation in depositional environments where this may be a problem (Alexanderson & Murray 2012; Kars *et al.* 2014). Analysis of modern sediments from Sjuøyane show close
<figure><img src="image_8.png" /><figcaption>Fig. 5. A–C. Sedimentological logs from the sections in Sandvika, Parryøya. The locations of the sections are shown in Fig. 1B. D. View towards the southwest of the study site. Person for scale. For lithofacies codes and legend to symbols, see Fig. 4. Details on radiocarbon ages (italics) and OSL ages are provided in Tables 1, 2.</figcaption></figure>

to zero year pIRIR<sub>225</sub> ages (H. Alexanderson, unpublished), which supports sufficient bleaching, while, in contrast, residual doses ('unbleachable component') are high for some samples (up to 88 Gy; Table S3). Dose recovery results also show that pIRIR<sub>225</sub>, at least for some samples, may overestimate the true dose, while the IR<sub>50</sub> may underestimate high doses (Data S1). Given these uncertainties, both IR<sub>50</sub> and pIRIR<sub>225</sub> ages need to be treated with some caution.

We obtained 14 luminescence ages from the shallow (glacio-)marine or littoral sediments constituting LA 2 on Phippsøya (Fig. 4, Table 2), and three luminescence ages from LA 2 in the Sandvika sections, Parryøya (Fig. 5, Table 2). The luminescence ages range from 87±12 ka at the base of the Utkiksnosa section to 29±3 ka at the upper part of the LA 2 sediments at Trolldoden 2. Ten of the 14 samples yield ages within MIS 3, and we interpret the sediments to be deposited during

<table><caption>Table 2. Luminescence ages from Sjuøyane. See also Data S1.</caption><thead><tr><th>Site</th><th>Lab. ID</th><th>IR50 age (ka)</th><th>No. of aliquots</th><th>pIRIR225 age (ka)</th><th>No. of aliquots</th></tr></thead><tbody><tr><td>Utkiksnosa</td><td>16019</td><td>105.6±9.4</td><td>8/9</td><td>87±12</td><td>8/9</td></tr><tr><td>Eidsbukta</td><td>16020</td><td>71.4±5.6</td><td>12/13</td><td>69.6±5.4</td><td>10/13</td></tr><tr><td>Eidsbukta</td><td>16021</td><td>68.0±4.8</td><td>11/12</td><td>82.8±6.1</td><td>10/12</td></tr><tr><td>Sandvika 2</td><td>16022</td><td>8.4±0.5</td><td>11/11</td><td>9.6±0.5</td><td>10/11</td></tr><tr><td>Sandvika 3</td><td>16023</td><td>6.1±0.3</td><td>14/14</td><td>8.1±0.4</td><td>14/14</td></tr><tr><td>Sandvika 1</td><td>16024</td><td>9.1±0.4</td><td>12/12</td><td>11.1±0.7</td><td>12/12</td></tr><tr><td>Horgvika</td><td>16025</td><td>38.6±2.3</td><td>12/12</td><td>42.3±3.4</td><td>10/12</td></tr><tr><td>Horgvika</td><td>16026</td><td>38.3±3.5</td><td>12/12</td><td>37.5±3.7</td><td>10/12</td></tr><tr><td>Horgvika</td><td>16027</td><td>49.3±2.8</td><td>12/12</td><td>48.7±3.4</td><td>10/12</td></tr><tr><td>Horgvika</td><td>16028</td><td>36.7±3.3</td><td>11/12</td><td>40.2±3.6</td><td>11/12</td></tr><tr><td>Isflakbukta 1</td><td>16029</td><td>22.4±1.9</td><td>15/15</td><td>33.6±2.3</td><td>10/15</td></tr><tr><td>Isflakbukta 1</td><td>16030</td><td>18.9±1.3</td><td>11/11</td><td>28.1±2.1</td><td>10/11</td></tr><tr><td>Trolldoden 1</td><td>18017</td><td>37.6±3.7</td><td>15/15</td><td>32.8±5.2</td><td>15/15</td></tr><tr><td>Trolldoden 1</td><td>18018</td><td>45.9±2.6</td><td>15/15</td><td>39.1±6.0</td><td>15/15</td></tr><tr><td>Trolldoden 1</td><td>18019</td><td>33.8±2.0</td><td>15/15</td><td>28.9±5.4</td><td>12/15</td></tr><tr><td>Trolldoden 2</td><td>18020</td><td>41.8±2.6</td><td>19/19</td><td>42.5±5.2</td><td>17/19</td></tr><tr><td>Trolldoden 2</td><td>18021</td><td>28.0±1.7</td><td>15/15</td><td>29.3±3.2</td><td>15/15</td></tr><tr><td>Isflakbukta 2</td><td>18022</td><td>139±17</td><td>18/18</td><td>76±11</td><td>15/18</td></tr><tr><td>Isflakbukta 2</td><td>18023</td><td>109.7±7.4</td><td>12/12</td><td>46.3±5.1</td><td>10/12</td></tr></tbody></table>

MIS 3. The remaining four ages range from 87 to 70 ka, and are regarded as overestimated, likely because of incomplete bleaching (e.g. Alexanderson & Muray 2012). The non-finite radiocarbon age (>40 ka BP; Lab. no. Ua-54598) from LA 2 at Utkiksnosa overall agrees with the MIS 3 luminescence ages (Fig. 4, Tables 1, 2). The ages from Sandvika are 11.1±0.7, 9.6±0.5 and 8.1±0.4 ka. They agree well with the median age of 10.7 cal. ka BP of radiocarbon age Ua-54599 (Table 1), which supports the accuracy of the pIRIR<sub>225</sub> ages. We therefore interpret the LA 2 sediments in Sandvika as deposited during the Early Holocene.

Only one sample from the base of LA 3 was collected for luminescence dating from the Isflakbukta 1 section (Fig. 4C, Table 2). It yields a mean age of 34±2 ka. Radiocarbon age Ua-54600, collected from LA 3 in the same section (Fig. 4C, Table 1) gives a median age of 10.4 cal. ka BP. This radiocarbon age does not agree with the pIRIR<sub>225</sub> age of 34±2 ka (sample 16029); neither does it agree with a pIRIR<sub>225</sub> age of 28±2 ka (sample 16030) from the base of LA 4 in the same section (Fig. 4C, Table 2). Minimum age modelling of small (1-mm) aliquot data from sample 16029 is not able to extract an age consistent with the radiocarbon age (Table 2). Additionally, the agreement of the uncorrected pIRIR<sub>225</sub> age (34±2 ka; Table 2) and the fading corrected IR<sub>50</sub> age (32±3 ka; Table S4) for this sample lends support to its accuracy. Because of the stratigraphical context of the radiocarbon sample, we regard it as too young although the technical quality of the sample is normal. This is because the LA 3 sediments are overlain by prograding beach-face sediments (LA 4) deposited during regression, i.e. a typical deglacial sediment (Mangerud et al. 1998; Alexanderson et al. 2011). Further, LA 4 at Isflakbukta 1 correlates with similar facies associations to the north and east (Fig. 4C, G).
## Geomorphological evidence of a high relative sea level

The foot of Hytteberget in western Isflakbukta, Phippsøya (Fig. 1B) is characterized by a clear bedrock erosional notch with wave-eroded bedrock, large water-worn boulders, and rounded cobbles (Fig. 2D). In many places, the rounded boulders and cobbles are partially overlain by angular clasts from the cliff above due to frost shattering and rockfalls. The elevation of this erosional notch was surveyed to 36±1 m a.h.t. This elevation is higher than the established postglacial marine limit at 22±1 m a.h.t. (Forman & Ingólfsson 2000). We interpret the erosional notch as formed prior to the postglacial marine limit; most likely during a Weichselian interstadial (e.g. Salvigsen 1979; Salvigsen & Nydal 1981; Forman et al. 2004).

## Cosmogenic exposure ages

*Martensøya.* – Sampling site 7ISL-2016-A2 is located on a ridge at the southernmost tip of a small mountain, Bratthovden (Fig. 1B). The bedrock ridge is situated between two raised beach plains to the northwest and

east, respectively. A red, medium-grained erratic granite boulder was sampled at 85 m a.s.l. (Fig. 6A). The boulder yields an age of 14.7±1.82 ka (Fig. 7, Table 3). We interpret the age as the minimum age of the last deglaciation of this site.

*Parryøya.* – Three boulder samples and one bedrock sample were obtained from this site at 109–196 m a.s.l. The locality is the southern part of the mountain Øykollen (Figs 1B, 6B, E). Sample lithology is granite and migmatite. Samples 7ISL-2016-B28 (boulder) and 7ISL-2016-B29 (bedrock) are located ~50 m apart and yield ages of 44.36±3.63 and 43.49±4.59 ka, respectively (Fig. 7, Table 3). The ages overlap within the 1σ internal uncertainties, and we suggest the two samples experienced the same exposure history. Possibly the site was exposed in MIS 3, and not glacially eroded during MIS 2.

Samples 7ISL-2016-B31 (boulder; 196 m a.s.l.) and 7ISL-2016-B32 (boulder; 163 m a.s.l.) are located in the higher part of Parryøya ~500 m apart, and yield ages of 18.94±3.26 and 22.89±4.05 ka, respectively (Fig. 7, Table 3). The ages overlap within the 1σ internal

<figure><img src="image_9.png" /><figcaption>Fig. 6. Sampling localities for cosmogenic exposure dating. A. Martensøya, southwest Bratthovden (sample 7ISL-2016-A2). B–E. Parryøya, southeast Øykollen (samples 7ISL-2016-B28, 7ISL-2016-B29, 7ISL-2016-B31 and 7ISL-2016-B32). F–I. Phippsøya, southwest Høgberget (samples 7ISL-2016-C1, 7ISL-2016-C2, 7ISL-2016-C3 and 7ISL-2016-C4).</figcaption></figure>
<figure><img src="image_10.png" /></figure>

**Fig. 7.** Probability distributions of the $^{10}$Be exposure ages of bedrock (black) and boulders (grey) from Sjuøyane. The $^{10}$Be ages are presented as normal kernel density plots using the iceTEA tool (Jones *et al.* 2019). A. All ages. The summed distribution (bold) is shown even though a $\chi^2$ test showed that there is less than 95% probability that the data set represents one population. When considering the ages as one population, the modal age is 44.72 ka and the weighted mean age is 29.5±11.25 ka. B. The sample from Martensøya (7ISL-2016-A2). C. The samples from Parryøya (7ISL-2016-B28 and 7ISL-2016-B29), sampled at the same locality. The weighted mean age is indicated. D. The samples from Parryøya (7ISL-2016-B31 and 7ISL-2016-B32). The weighted mean age is indicated. E. The samples from Phippsøya (7ISL-2016-C1, 7ISL-2016-C2, 7ISL-2016-C3 and 7ISL-2016-C4). The summed distribution (bold) is shown even though a $\chi^2$ test showed that there is less than 95% probability that the data set represents one population.

uncertainties, and we suggest the two samples experi-
enced the same exposure history. Assuming that the
average age of 20.7±1.96 ka represents the time of
the last deglaciation of the site, it suggests that at least
the higher elevation parts of the area were ice-free at
this time.

*Phippsøya.* – Three bedrock samples and one boulder sample were obtained from this site (Figs 1B, 6F, I). The locality is a hill on the southwestern part of the mountain Høgberget. Sample lithology is granite. The ages of the samples are 46.94±4.49 ka (bedrock; 7ISL-2016-C1), 36.34±2.46 ka (bedrock; 7ISL-2016-C2), 33.01±3.97 ka (boulder; 7ISL-2016-C3) and 25.39±2.44 ka (bedrock; 7ISL-2016-C4) (Fig. 7, Table 3). Two of the four ages overlap within the 1σ internal uncertainties, and we suggest the two samples experienced the same exposure history. However, the three oldest samples are of MIS 3 age, and indicate a complex exposure history. Possibly the site was exposed in MIS 3, and not glacially eroded during MIS 2.

Discussion

*Sedimentary successions on Sjuøyane and implications for*
*the glacial history*

The majority of the sections consist of the (glacio-) marine and littoral sediments of LA 2 observed in all the sections on Phippsøya and Parryøya (Figs 4, 5), and the OSL ages indicate that LA2 was deposited during MIS 3 at Phippsøya (Fig. 8). The LA 2 sediments and the presence of the bedrock erosional notch with wave-washed bedrock and rounded boulders at 36±1 m a.h.t. on Phippsøya suggest that they formed during a high relative sea level, probably caused by glacio-isostatic depression following the MIS 4 glaciation of Svalbard (Forman & Ingólfsson 2000; Ingólfsson & Landvik 2013; Alexanderson *et al.* 2018). A MIS 3 age is supported by
<table><caption>Table 3. Summary of <sup>10</sup>Be data and cosmogenic exposure ages from Sjuøyane, Svalbard. See also Tables S5, S6 and Data S2.</caption><thead><tr><th>Sample ID</th><th>Latitude (°N)</th><th>Longitude (°E)</th><th>Altitude (m a.s.l.)</th><th>Sample type</th><th>Lithology</th><th>Thickness (cm)</th><th>Shielding factor</th><th>Quartz (g)</th><th><sup>9</sup>Be carrier weight (g)</th><th><sup>10</sup>Be conc. (atoms g<sup>-1</sup>) × 10<sup>4</sup></th><th><sup>10</sup>Be uncert. (atoms g<sup>-1</sup>) × 10<sup>4</sup></th><th><sup>10</sup>Be age (ka)</th><th>1σ internal uncert. (ka)</th><th>1σ external uncert. (ka)</th></tr></thead><tbody><tr><td>7ISL-2016-A2</td><td>80.68572</td><td>21.25531</td><td>85</td><td>Boulder</td><td>Granite</td><td>3.5</td><td>0.980146</td><td>20.2500</td><td>0.466153</td><td>6.214</td><td>0.775</td><td>14.70</td><td>1.82</td><td>1.9</td></tr><tr><td>7ISL-2016-B28</td><td>80.64578</td><td>20.62706</td><td>109</td><td>Boulder</td><td>Granite</td><td>4.5</td><td>1</td><td>24.1326</td><td>0.461330</td><td>19.357</td><td>1.593</td><td>44.36</td><td>3.63</td><td>3.99</td></tr><tr><td>7ISL-2016-B29</td><td>80.64632</td><td>20.62603</td><td>109</td><td>Bedrock</td><td>Granite</td><td>3</td><td>1</td><td>20.6757</td><td>0.463678</td><td>19.223</td><td>2.040</td><td>43.49</td><td>4.59</td><td>4.87</td></tr><tr><td>7ISL-2016-B31</td><td>80.64322</td><td>20.60873</td><td>196</td><td>Boulder</td><td>Granite</td><td>4</td><td>1</td><td>19.3073</td><td>0.465245</td><td>91.961</td><td>1.589</td><td>18.94</td><td>3.26</td><td>3.33</td></tr><tr><td>7ISL-2016-B32</td><td>80.64129</td><td>20.63376</td><td>163</td><td>Boulder</td><td>Migmatite</td><td>2.5</td><td>1</td><td>18.5122</td><td>0.465850</td><td>10.840</td><td>1.933</td><td>22.89</td><td>4.05</td><td>4.15</td></tr><tr><td>7ISL-2016-C1</td><td>80.70627</td><td>20.88935</td><td>81</td><td>Bedrock</td><td>Granite</td><td>1.5</td><td>1</td><td>0.999689</td><td>22.5029</td><td>0.459666</td><td>20.315</td><td>1.952</td><td>46.94</td><td>4.83</td></tr><tr><td>7ISL-2016-C2</td><td>80.70689</td><td>20.89089</td><td>105</td><td>Bedrock</td><td>Granite</td><td>4</td><td>1</td><td>0.998244</td><td>22.4189</td><td>0.463580</td><td>15.852</td><td>1.079</td><td>36.34</td><td>2.46</td><td>2.81</td></tr><tr><td>7ISL-2016-C3</td><td>80.70596</td><td>20.88905</td><td>113</td><td>Boulder</td><td>Granite</td><td>1</td><td>1</td><td>0.999168</td><td>20.6355</td><td>0.469480</td><td>14.921</td><td>1.803</td><td>33.01</td><td>3.97</td><td>4.16</td></tr><tr><td>7ISL-2016-C4</td><td>80.70505</td><td>20.88652</td><td>110</td><td>Bedrock</td><td>Granite</td><td>3.5</td><td>1</td><td>0.999168</td><td>20.1170</td><td>0.467665</td><td>11.226</td><td>1.086</td><td>25.39</td><td>2.44</td><td>2.62</td></tr></tbody></table>

our non-finite radiocarbon age Ua-54598 and radiocarbon age GX-22388 of Forman & Ingólsson (2000) yielding a median age of 50.5 cal. ka BP from the same site in Horgvika (Tables 1, S1). Glaciomarine conditions during MIS 3 agree with the glacial history of western Spitsbergen and elsewhere on Svalbard, where e.g. marine sediments from the Kapp Ekholm interstadial demonstrate ice-free environments (Fig. 8C; Mangerud et al. 1998; Ingólsson & Landvik 2013). Nordaustlandet was also ice-free during this Middle Weichselian interstadial, as indicated by the shallow marine or littoral sediments of Unit 6 in Isvika (Fig. 8D; Kaakinen et al. 2009), radiocarbon ages of marine bivalve shells from tills and marine sediments on NW Nordaustlandet (Blake 1989), and marine shell fragments emerging at the surface in Palanderbukta, SW Nordaustlandet (Scho-macker et al. 2019).

Chauhan et al. (2016) analysed ice-rafted debris (IRD) in a marine sediment core from the shelf north-northeast of Nordaustlandet (HH11-09GC; Fig. 1). They suggested that the IRD peak during MIS 4 is caused by the advance of the SBIS (Fig. 8E), which agrees with the terrestrial evidence from Nordaustlandet (Kaakinen et al. 2009). The smaller IRD peak at the MIS 4/3 transition is interpreted to be caused by iceberg and/or sea-ice melting events during the disintegration of the SBIS. The IRD peak c. 30 cal. ka BP could reflect deposition from local slope failure rather than from icebergs, and it is not found in core JM10-02GC further southwest on the northern slope (Chauhan et al. 2016; Fig. 1). Our OSL ages suggest that the LA 2 sediments were still forming at this time (Fig. 8A). The IRD peaks during MIS 2 reflect the advancing SBIS at the LLGM and the deglaciation (Fig. 8E; Chauhan et al. 2016). The glacial drift above the postglacial marine limit described by Forman & Ingólsson (2000) likely formed during the LLGM and its marine bivalve shell fragments dated to 42.7 cal. ka BP (Table S1) provides a maximum age. The source of the shells is likely to be the LA 2 sediments. We did not observe a glacial drift (basal till) in the sedimentological sections, and the stratigraphical association of the patchy glacial drift on the surface is not known. It might correlate to the diamict of LA 3. In Isvika, Nordaustlandet, a reddish basal till sandwiched between littoral sediments that were OSL dated to c. 40.0 and 10.6 ka, respectively, provides terrestrial evidence of a Late Weichselian glaciation in the region (Kaakinen et al. 2009). A detailed mapping of the distribution and sedimentology of the glacial drift on Sjuøyane could possibly provide data about the basal thermal conditions at the northern margin of the SBIS during deposition. Generally, the patchy glacial drift and well-preserved pre-Late Weichselian sediments suggest that the Late Weichselian glaciation was non-erosive and/or cold based, and probably of short duration. A similar pattern was observed on Nordaustlandet (Österholm 1990; Kaakinen et al. 2009). Together, these sites point towards
<figure><img src="image_11.png" /><figcaption>Fig. 8. A. Overview of the optically stimulated luminescence (OSL, in ka), radiocarbon ($^{14}$C, in cal. ka BP), and cosmogenic nuclide (CN, in ka) ages from Sjuøyane. B. Major depositional environments on Sjuøyane. C. Glaciation curve for western Spitsbergen after Mangerud *et al.* (1998) and Ingólfsson & Landvik (2013). D. Major depositional environments on Nordaustlandet (Isvika; Kaakinen *et al.* 2009). E. Concentration of ice-rafted debris (IRD) per gram dry weight of sediment in sediment core HH11-09GC at the northern Svalbard margin, northeast of Nordaustlandet (Chauhan *et al.* 2016).</figcaption></figure>

limited Late Weichselian glacial activity along this part of the northern SBIS margin.

We interpret LA 4 on Phippsøya as prograding beach-
face sediments deposited during regression (Fig. 4). At
Trollodden, Forman & Ingólfsson (2000) radiocarbon
dated a *Balanus balanus* sampled in a cliff section of sandy,
littoral foreset beds grading into a raised beach, yielding a
median age of 10.6 cal. ka BP (Table S1). This suggests that
the LA 4 sediments were deposited during the last
deglaciation. Similar sediments formed in Isvika, Nor-
daustlandet, at this time (Kaakinen et al. 2009) and at
numerous other localities in Svalbard experiencing
postglacial emergence (Forman et al. 2004).
Although finer-grained, the LA 2 sediments in Sandvika,
Parryøya, corroborate the reconstruction of this environ-
ment (Fig. 5). These sediments formed during the Early
Holocene in a sheltered bay during regression caused by
the postglacial isostatic rebound. The LA 2 and 4
sediments and the postglacial marine limit at ~22±1 m

a.h.t. provide clear terrestrial evidence of glaciation during
the LLGM. Unfortunately, we were not able to find datable
material on raised beaches to improve the postglacial
relative sea level curve from Sjuøyane (Forman &
Ingólfsson 2000). A better-constrained relative sea level
curve from Sjuøyane could provide a better understanding
of the glacio-isostatic rebound and, hence, the thickness
and duration of glaciation at the north margin of the SBIS
(e.g. Forman *et al.* 2004).

Cosmogenic exposure ages and implications for the glacial
history

The nine exposure ages from Sjuøyane range from 46.94
to 14.70 ka (Figs 7, 8, Table 3), and the data set does not
reveal a well-constrained deglaciation age for the
archipelago. However, the ages provide information
about the exposure history of each site. The two highest
boulder samples (163 and 196 m a.s.l.) from Parryøya
overlap within 1σ and have an average age of 20.7±1.96 ka (Fig. 7D). They suggest that at least the higher parts of Sjuøyane were ice-free at this time. The boulder age of 14.70±1.82 ka from Martensøya (85 m a.s.l.) also indicates ice-free conditions by then (Fig. 7B). These data from Parryøya and Martensøya could support a conceptual glaciation model with active ice in the troughs on the continental shelf along the north margin of the SBIS and less active (or cold-based) ice between the troughs (Landvik *et al.* 2005; Ingólfsson & Landvik 2013). The remaining six exposure ages are LGM and older, and we do not interpret them as last deglaciation ages. At Parryøya, a bedrock (7ISL-2016-B29) and boulder (7ISL-2016-B28) age overlap within 1σ and have an average of 43.98 ka (Fig. 7C). Although samples 7ISL-2016-C2 and 7ISL-2016-C3 from Phippsøya overlap within 1σ, the scattered age distribution of the four samples from Phippsøya prevents a clear interpretation of the timing of the last deglaciation from the complex exposure history (Fig. 7E).

The low number of cosmogenic exposure ages from Sjuøyane restricts their significance for constraining the glacial history of Sjuøyane. We note that the youngest age of 14.70±1.82 ka from Martensøya is obtained from a red granite boulder (Fig. 6A) with a likely provenance from Nordaustlandet (Forman & Ingólfsson 2000). This would indicate active ice flow from the south during the Late Weichselian. It is likely that the samples that predate the last deglaciation are affected by inheritance and reflect repeated exposure during the Weichselian. A similar pattern of exposure ages was observed from highlands on Nordaustlandet, where boulders and bedrock samples consistently yielded ages older than the last deglaciation; however, without clustering significantly in other age intervals (Hormes *et al.* 2011). Hormes *et al.* (2011) interpreted the ages to be caused by cosmogenic isotope inheritance and suggested that the highlands experienced periods of non-erosive cold-based glaciation during the Weichselian. Hormes *et al.* (2011) suggested that the ¹⁰Be exposure ages of 64–68 ka from highlands in Prins Oscars Land could reflect that the area was ice-free during MIS 2 and that the MIS 4 glaciation was more extensive. Similarly, ¹⁰Be exposure ages from Amsterdamøya, NW Svalbard, suggest that the highlands (>300 m a.s.l.) were last glaciated >80 ka ago (Landvik *et al.* 2003). Our ¹⁰Be ages from Sjuøyane are from MIS 2–3 (Fig. 8), and do not reveal whether this was also the case on Sjuøyane. However, the evidence of a higher relative sea level at 36±1 m a.h.t. on Phippsøya suggests that the archipelago was glacio-isostatically depressed at a time prior to the LGM. This could have been caused by glaciation during MIS 4.

## Holocene environments

The lake sediments from Isvatnet show that organic sedimentation was taking place 7.0 cal. ka BP (Fig. 3,

Table 1). Because datable material is lacking from the glaciolacustrine sediments (LU 1), we are not able to determine the age of this environment. However, Isvatnet is situated above the postglacial marine limit (Forman & Ingólfsson 2000), and it is likely that the glaciolacustrine sediments formed during the last deglaciation when meltwater last drained into the basin. The gyttja (LU 2) constituting the upper part of the lake sedimentary record shows constant sedimentation since 7.0 cal. ka BP (Fig. 3B) and no evidence of major environmental change.

On Parryøya, the two moss kill ages of 3.8 and 2.8 cal. ka BP (Fig. 2C, Table 1) suggest Neoglacial cooling, with expanding snow patches killing mosses growing near their margins. This agrees with ages of killed vegetation from central Spitsbergen, showing snowline lowering since at least 4.0–3.4 cal. ka BP (Miller *et al.* 2017) and with glacier expansion in northern Svalbard (Allaart *et al.* 2021).

## Conclusions

* Terrestrial Quaternary geological data from Sjuøyane provide insight into the depositional environments during the Weichselian and Holocene. Our empirical data are important to validate and discuss conceptual and numerical models of the Svalbard–Barents Sea Ice Sheet, for example by providing ages and duration of ice-free periods (e.g. MIS 3) along the northern ice-sheet margin.

* Shallow marine and/or littoral sediments (LA 2) occur in the coastal sections of Phippsøya and Parryøya. Their ¹⁴C and feldspar luminescence ages indicate ice-free conditions on Sjuøyane during MIS 3. The sediments formed during high relative sea level, most likely following the MIS 4 glaciation on Svalbard. On Parryøya, ¹⁴C and OSL ages show that Sjuøyane were ice-free by c. 11.1 ka and that sedimentation took place in a shallow marine environment during regression caused by glacio-isostatic rebound. A bedrock erosional notch and rounded boulders provide evidence of a higher relative sea level at 36±1 m a.h.t. on Phippsøya. This level is higher than the postglacial marine limit and pre-dates the LGM.

* Red granite erratics on Sjuøyane indicate glacial transport from Nordaustlandet. One such granite boulder from lowlands on Martensøya yielded an age of 14.7±1.82 ka, reflecting the last deglaciation. Two boulder samples from Parryøya with ages of 18.94±3.26 and 22.89±4.05 ka suggest that the highlands were ice-free at this time. Cosmogenic nuclide datings of erratics and bedrock elsewhere on Sjuøyane pre-date the last deglaciation and reveal a complex exposure history, possibly due to repeated, cold-based glaciations. The patchy glacial drift at the
surface and the well-preserved pre-Late Weichselian sediments suggest non-erosive and/or cold-based Late Weichselian glaciation.

*In situ*-killed moss sampled at the margin of a receding snow patch in Sandvika, Parryøya, yields radiocarbon median ages of 3.8 and 2.8 cal. ka BP. This indicates snow patch expansion in a deteriorating climate (Neoglacial cooling) at that time. Radiocarbon dating of a lacustrine sediment core from Isvatnet shows that gyttja has been accumulating at least since 7.0 cal. ka BP.

*The terrestrial northern margin of the Svalbard-Barents Sea Ice Sheet at Sjuøyane was characterized by non-erosive and/or cold-based glaciation during the LLGM. The pre-Late Weichselian relative sea level indicator at 36±1 m a.h.t. and ubiquitous raised marine sediments of MIS 3 age could indicate that the glaciation during MIS 4 was more extensive than during the Late Weichselian at this part of the Svalbard-Barents Sea Ice Sheet.*

*Acknowledgements.* – Fieldwork at Sjuøyane was conducted during the University Centre in Svalbard (UNIS) graduate student course AG-348/848 in 2016 and 2018. For field assistance, we thank the students on the course, Anne E. Elink, and Marc Macias-Fauria. We thank Anna Hughes and an anonymous reviewer for constructive comments that improved the manuscript. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

*Author contributions.* – AS: conceptualization, investigation, visualization, writing – original draft, project administration, funding acquisition. HA: conceptualization, investigation, visualization, writing – original draft, funding acquisition. WRF: investigation, writing – review & editing, funding acquisition. MFAF: investigation, writing – review & editing. SEK: investigation, visualization, writing – original draft. NK: investigation, writing – review & editing. ESE: investigation, writing – review & editing. RN: investigation, writing – review & editing. VJ: investigation, writing – review & editing. ÓI: writing – review & editing.

*Data availability statement.* – The data that support the findings of this study are available in the Supporting Information of this article.

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## Supporting Information

Additional Supporting Information to this article is available at http://www.boreas.dk.

*Data S1.* Preparation, measurement, and age calculation for luminescence samples.

*Data S2.* Raw data for calculation of ¹⁰Be exposure ages.

*Fig. S1.* Examples of growth and decay curves from sample 16029 (1-mm aliquots).

*Fig. S2.* Dose recovery for A. IR<sub>50</sub> and B. pIRIR<sub>225</sub>. Ideally the measured dose should equal the given dose within ±10%.

*Fig. S3.* Examples of fading determinations, here sample 16029.

*Fig. S4.* Abanico plots of the dose distributions for sample 16029 (1-mm aliquots).

*Table S1.* Re-calibrated radiocarbon ages from Sjuøyane, Nordaustlandet, and the continental shelf and upper slope north of Nordaustlandet, Svalbard. Ages from publications are re-calibrated in OxCAL v4.4. using Marine20 (Heaton et al. 2020) and a ΔR value of -61±37 years for shells and foraminifera and -160±41 years for whalebones (Pienkowski et al. 2022). All radiocarbon ages are shown in the table with reference to the original study.

*Table S2.* Dose rate data. Sediment nuclide concentrations as determined from high-resolution gamma spectrometry, cosmic dose rate and total environmental dose rate calculated in DRAC (Durcan et al. 2015), and sediment water content (field, saturated, and estimated average since time of deposition).

*Table S3.* pIRIR<sub>225</sub> luminescence data. Corrected ages are corrected for fading according to Huntley & Lamothe (2001) using the calc_FadingCorr() function in the RLuminescence package (Kreutzer 2021). The residual dose has not been subtracted.

*Table S4.* IR<sub>50</sub> luminescence data. Corrected ages are corrected for fading according to Huntley & Lamothe (2001) using the calc_FadingCorr function in the RLuminescence package (Kreutzer 2021). The residual dose has not been subtracted.

*Table S5.* Full ¹⁰Be data set and data for calculation of cosmogenic exposure ages from Sjuøyane, Svalbard.

*Table S6.* Full ¹⁰Be data set and data for calculation of cosmogenic exposure ages from Sjuøyane, Svalbard.