THE LAST GLACIAL MAXIMUM OF SVALBARD AND THE BARENTS SEA AREA: ICE SHEET EXTENT AND CONFIGURATION
Abstract
The timing, extent and configuration of the Late Weichselian Barents ice sheet has been debated for several decades. This debate has arisen largely because of the limited or conflicting field evidence on which most models have been based. In particular, reconstruction of the marine parts of the former Barents ice sheet has been controversial. This paper aims to review the geological observations and interpretations regarding the size and timing of the Late Weichselian ice sheet, combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour. Sub-glacial till with overlying glacimarine deposits dated to the Late Weichselian is found over most of the Barents Sea floor and the continental shelf west of Svalbard. Glacially induced debris flow deposits on the large Bjønøya and Isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation. Isobase maps show a centre of post-glacial uplift in the north-central Barents Sea, and glaciological and isostatic modelling suggest that the ice sheet was 2000–3000 m thick in this area. The ice sheet was confluent with ice over the Kara Sea, but the interaction between the Barents and Kara ice sheets is not yet fully understood. The deglaciation of the Barents ice sheet started ca 15 ka, probably by calving within the deeper troughs. By 12 ka, most of the central Barents Sea was ice free, and ice remained over the Svalbard, Franz Josef Land and Novaja Zemlya archipelagos and adjacent shallow shelf areas. The coasts and fjords of these islands were ice free by 10 ka.
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The areas covered by permafrost in the polar regions are vulnerable to rapid changes in the current climate. The well-studied near-surface active layer and permafrost zone are in contrast to the unknown exact shape of the bottom permafrost boundary. Therefore, the entire shape of permafrost between the upper and lower boundaries is not identified with sufficient accuracy. Since most of the factors affecting deep cryotic structures are subsurface in nature, their evolution in deeper layers is also relatively unclear. Here, we propose a hypothesis based on the results of geophysical studies regarding the shape of the permafrost in the coastal area of Svalbard, Southern Spitsbergen. In the article, we emphasize the importance of recognizing not only the uppermost active layer but also the bottom boundary of permafrost along with its transition zone, due to the underestimated potential role of its continuity in observing climate change. The lower permafrost boundary is estimated to range from 70 m below the surface in areas close to the shore to 180 m inland, while a continuous layer of an entirely frozen matrix can be identified with a thickness between 40 m and 100 m. We also hypothesized the presence of the possible subsea permafrost in the Hornsund. The influence of seawater intrusions, isostatic uplift of deglaciated areas, and surface-related processes that affect permafrost evolution may lead to extensive changes in the hydrology and geology of the polar regions in the future. For all these reasons, monitoring, geophysical imaging and understanding the characteristics and evolution of deep permafrost structures requires global attention and scientific efforts.
Geoelectrical properties of saline permafrost soil in the Adventdalen valley of Svalbard (Norway), constrained with in-situ well data
2021, Journal of Applied GeophysicsDirect Current (DC) Resistivity and Induced Polarization (IP) response of six profiles were measured using the Gradient electrode configuration in Adventdalen, Svalbard, to characterise the near-surface stratigraphy of the soil and to account for geotechnical and environmental aspects of global warming in the arctic region. In addition, Wenner array data was collected for the selected profiles to examine its effectiveness as compared to the Gradient array, given the characteristics of the study site. Two commercial inversion software programs, Res2DINV and AarhusINV, were used for the inversion of the DC resistivity and IP data, to compare the software. Physical soil properties, including porosity, water saturation, water salinity, freezing temperature and grain size distribution, previously measured from samples retrieved from wells along the studied profiles, were integrated in this study to investigate the correlation with geoelectrical properties of the sediments inferred from the DC resistivity and IP data.
Results from processing of the Wenner array DC resistivity data provided higher resolution as compared to the Gradient array data, especially from deeper parts of the models, due to its higher signal-to-noise ratio. The Wenner array data also indicated better inversion result for the IP data as distinctive anomalies were better indicated in data from Wenner array survey. The Wenner array data also provided a realistic trend for the anomalies, thanks to the symmetrical geometry of the electrodes during the survey, although at the cost of time and higher expenses. Inversion results proved that AarhusINV resolved the geometry of the subsurface layers with higher resolution compared with the Res2DINV. However, the two inversion algorithms use slightly different parameters for the processing and for presenting the results, thus only allowing qualitative comparison. Based on the interpretations of the DC resistivity and IP data, four distinctive zones were identified from the surface to the maximum depth of 26 m, consisting of (i) unfrozen active-layer-(silts and sands), with intermediate resistivity values 200–300 Ω·m; (ii) frozen soil with 3–10 m thickness and resistivity values between 2500 and 5000 Ω·m; (iii) unfrozen soil (cryopeg) with high salinity and low resistivity of 40 Ω·m; and finally (iv) clayey-unfrozen soil sediments with low resistivity ranging 10–20 Ω·m, at depths between 13 and 26 m. The IP data allowed for the delineation of a low chargeability zone near the surface and a high chargeability zone at greater depth which denote the active layer, lower parts of unfrozen soil sediments and cryopeg respectively, within the top 10 m of the subsurface.
The 3D subsurface model of the study area was created based on interpretations of the DC resistivity and IP data and was constrained by the description of the subsurface stratigraphy from nearby wells, which provided detailed information about the vertical stratigraphy of the study area. In addition, a good correlation was observed between the studied physical properties of the sediments and the DC resistivity data for the intersecting profile SVAER04, as the interface between high and low resistivity data at ca. 10 m depth coincided the sedimentary formation with intermediate-fine grain size, high porosity, high water saturation and high salt content. Our findings show that joint application of the geoelectrical surveys and laboratory analysis of soil samples are an efficient complement to each other. These methods can be used as an alternative to each other to investigate larger areas where achieving high resolution data is not necessary.
Our study results underline the importance of choosing the right survey design for collecting the DC resistivity and IP data. Contribution of the IP data in this study mostly concerns the shallow parts of the subsurface due to the low signal-to-noise ratio at greater depths, and frozen ground which limited the ion mobility and hence the IP response. An appropriate inversion program coupled with integration of the physical properties of the sediments, can be successfully applied to characterise the near-surface morphology of the sedimentary formations to address the geotechnical and environmental challenges related to the permafrost in the Arctic.
Glacial and environmental changes in northern Svalbard over the last 16.3 ka inferred from neodymium isotopes
2021, Global and Planetary ChangeThe reconstruction of past ice sheet extents and dynamics in polar regions is essential for understanding the global climate system and obtaining more reliable predictions of future climate change. Here, we present a multi-proxy dataset integrating the Nd isotopic compositions (εNd) of paired detrital and authigenic Fe oxide fractions, grain size distributions, organic geochemistry, and mineral assemblages in a glacimarine sediment core (core HH17–1085-GC) retrieved from the continental shelf off northern Svalbard. Our results indicate variability in sediment provenance and chemical weathering patterns since the last deglaciation, allowing us to distinguish a succession of distinct paleoclimate events: 1) a general retreat of the Svalbard-Barents Sea Ice Sheet (SBIS) from the continental shelf before ca. 16.3 ka BP; 2) an intense episode of meltwater discharge related to massive glacier loss between ca. 12.1–9.9 ka BP; and 3) a period of reduced meltwater input between ca. 9.9 and 2.7 ka BP followed by 4) a phase of glacier re-advance over the last two millennia. Evidence for the prolonged supply of radiogenic detrital εNd and dolomite at the site of core HH17–1085-GC indicates that the onset of deglaciation offshore northeastern Svalbard may have occurred at least 1 ka later than that at the northwestern shelf, which can be further evaluated by obtaining a more precise end-member determination for the northeastern source with a quantitative εNd dataset from Nordaustlandet. In the context where both polar sea-ice and oceanic circulation are expected to have played minor roles in determining the sedimentary εNd compositions, the evidence for pronounced Nd isotopic decoupling between paired authigenic and detrital signatures (ΔεNd) at ca. 15.2 and 14.1 ka BP is interpreted as reflecting chemical weathering changes following the retreat of the SBIS on northern Svalbard, probably corresponding to punctual episodes of glacial re-advances. Our findings provide a better understanding of the deglacial history of northern Svalbard during and after the last deglaciation and highlight the utility of Nd isotopes as a proxy for reconstructing paleo-cryosphere changes.
Geomorphology and surficial geology of the Femmilsjøen area, northern Spitsbergen
2021, GeomorphologyClimate change is amplified in the Arctic, and establishing baseline data for its current character is important. Here we present a map of the geomorphology of the Femmilsjøen area, Spitsbergen, northern Svalbard. The regional physiography is characterised by a low-relief, high elevation mountain plateau, its high-relief steep slopes, and low-relief coastal lowlands. The results indicate that glaciers were most likely warm-based and erosive in the low terrain, whereas there are signatures of colder, less erosive ice on the plateaus during the Late Weichselian. Our study highlights the ongoing glacial and periglacial morphological processes in an area of hard and weathering-resistant bedrock, situated in northern Svalbard.
Climate and ocean forcing of ice-sheet dynamics along the Svalbard-Barents Sea ice sheet during the deglaciation ∼20,000–10,000 years BP
2021, Quaternary Science AdvancesThe last deglaciation, 20,000–10,000 years ago, was a period of global warming and rapidly shrinking ice sheets. It was also climatically unstable and retreats were interrupted by re-advances. Retreat rates and timing relative to climatic changes have therefore been difficult to establish. We here study a suite of 12 marine sediment cores from Storfjorden and Storfjorden Trough, Svalbard. The purpose is to reconstruct retreat patterns and retreat rates of a high northern latitude marine-based ice stream from the Svalbard-Barents Sea Ice Sheet in relation to paleoceanographic and paleoclimatic changes. The study is based on abundance and composition of planktic and benthic foraminiferal assemblages, ice rafted debris (IRD), lithology, and 70 AMS-14C dates. For core 460, we also calculate sea surface and bottom water temperatures and bottom water salinity. The results show that retreat rates of the ice shelf and ice streams of Storfjorden Trough/Storfjorden (‘Storfjorden Ice Stream’) closely followed the deglacial atmospheric and ocean temperature changes. During the start of the Bølling interstadial retreat rates in Storfjorden Trough probably exceeded 2.5 km/year and more than 10,000 km2 of ice disappeared almost instantaneously. A similarly rapid retreat occurred at the start of the Holocene interglacial, when 4500 km2 of ice broke up. Maximum rates during the deglaciation match the fastest modern rates from Antarctica and Greenland. Correlation of data show that the ice streams in several fjords from northern Norway retreated simultaneously with the Storfjorden Ice Stream, indicating that temperature was the most important forcing factor of the Svalbard-Barents Sea Ice Sheet during the deglaciation.