Barents Sea Ice Sheet Research Articles

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

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 10Be 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 10Be 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.

Oil sands in glacial till as a driver of fast flow and instability in the former Laurentide Ice Sheet: Alberta, Canada

AbstractReconstructions of the southwestern Laurentide Ice Sheet (LIS) from geomorphology have revealed complex cross‐cutting ice streams, indicative of surging and flow switching. This flow pattern and behaviour is distinct from the rest of the ice sheet where ice streams flowed radially to the ice sheet margin. Many ice streams in the southwestern sector originate around the Alberta Oil Sands (AOS). Previous reports have detected oil sands material in surficial and glacial sediments south of the AOS, demonstrating potential glacial mobilisation of the oil sands. In this study, we use geochemical fingerprinting to systematically investigate surficial sediments from the former Central Alberta Ice Stream (CAIS) flow track. We compare the geochemical signatures of 82 sediments from within and outside the CAIS limits with those of the AOS (from mines and natural exposures), using gas chromatography–mass spectrometry oil–oil correlation techniques. Our results provide geochemical evidence of glacial erosion and long‐distance mobilisation of AOS producing contamination signatures in sediments throughout the CAIS flow track. The strength of the AOS signature is particularly strong in sediments along the terminating margins, to the east of Calgary and in the Cooking Lake area to the southeast of Edmonton. These results inform theoretical models of enhanced slipperiness, inspired by slippery liquid infused porous surfaces (SLIPS), whereby oil lubrication of the basal sediment influences the degree of sliding and basal deformation in the ice stream. We hypothesise that naturally occurring hydrocarbons at the basal interface exerted control on the location of the onset zone of the CAIS and surrounding ice streams in Alberta. The enhanced slipperiness caused by oil contamination may also explain ice streaming and surging in other ice sheets, such as the Barents Sea Ice Sheet, where hydrocarbons are known to have been driven to the sedimentary interface during glaciation.

Distinct modes of meltwater drainage and landform development beneath the last Barents Sea ice sheet

The flow of glacial ice is impacted by basal meltwater drainage systems that fluctuate on a continuum from distributed, high-pressure environments to channelized, lower pressure networks. Understanding the long-term development of dominant drainage modes and impacts on ice flow and landform development is a crucial step in predicting palaeo and contemporary ice-mass response to changes in climate. The spatial and temporal scales at which different drainage modes operate are largely unknown, and the geomorphological legacy of subglacial meltwater networks that evolve over a glaciation provide composite records of drainage system development. Here, we use high-resolution bathymetric data from shallow banks in the central Barents Sea to map the geomorphological imprint of meltwater drainage beneath the collapsing marine-based Barents Sea Ice Sheet (BSIS). We observe a succession of distinct meltwater landforms that provide relative timing constraints for subglacial drainage modes, indicating that extensive networks of channelized drainage were in operation during deglaciation. Interlinked basins and channels suggest that meltwater availability and drainage system development was influenced by filling and draining cycles in subglacial lakes. Networks of eskers also indicate near-margin meltwater conduits incised into basal ice during late-stage deglaciation, and we suggest that these systems were supplemented by increased inputs from supraglacial melting. The abundance of meltwater during the late stages of BSIS deglaciation likely contributed to elevated erosion of the sedimentary substrate and the mobilisation of subglacial sediments, providing a sediment source for the relatively abundant eskers found deposited across bank areas. A newly discovered beaded esker system over 67 km long in Hopendjupet constrains a fluctuating, but generally decelerating, pace of ice retreat from ∼1,600 m a−1 to ∼620 m a−1 over central Barents Sea bank areas during a 91-year timespan.

The geomorphic record of marine-based ice dome decay: Final collapse of the Barents Sea ice sheet

New high-resolution geophysical data acquired from eastern Storbanken in the central Barents Sea allow reconstruction of the flow of marine-based ice dome during the final stages of ice-sheet decay. Ice-marginal and subglacial landforms show diverging and quasi-radial grounding-line retreat patterns, implying that an isolated, dynamic, shrinking ice dome was centred at ∼77° N 40° E on eastern Storbanken prior to final marine-based ice-sheet collapse. This geomorphological reconstruction contrasts with previous numerical and observational models that infer a northward-migrating ice dome or crest that extended longitudinally from Svalbard to Franz-Josef Land prior to its eventual demise. Our results provide an important past analogue for late-stage decay of marine ice domes, as well as robust empirical constraints that can be used to calibrate numerical models simulating the behaviour of marine-based ice sheets in a warming environment.

Structural and fluid-migration control on hill-hole pair formation: Evidence from high-resolution 3D seismic data from the SW Barents Sea

Hill-hole pairs are subglacial landforms consisting of thrust-block hills and associated source depressions. Formed by evacuation of material where ice sheets have been locally frozen to the substrate, they give insights into paleo-ice-sheet dynamics. The aim of this study was to document the relationships between ancient hill-hole pairs identified on a buried glacial unconformity with the structure of the underlying sedimentary deposits, and then to determine if the basin geology and glacial fluid migration pathways promoted local subglacial freeze-on during the hill-hole pair formation. The study is based on seismic geomorphological interpretation of four high-resolution 3D seismic cubes covering an area of 800 km2 in the SW Barents Sea, and fluid seepage data from 37 gravity cores.The seismic datasets allowed the identification of 55 hill-hole pairs along the buried unconformity. The hills are characterized by chaotic to homogenous seismic facies forming up to 19 m high mounds, each covering areas of 2000–644,000 m2. The holes form depressions between 1 and 44 m deep and 2000–704,000 m2 in areal extent, which cut into preglacial Mesozoic bedrock and later infilled by glacial till. The holes are often found above fault terminations. High-amplitude reflections identified along the faults and in the strata below the holes are interpreted as shallow gas migrating upward towards the glacial unconformity. Geochemical data of the seabed sediment cores further indicates an association between hill-hole pair occurrence and present-day thermogenic hydrocarbon seepage.The hill-hole pairs geometries were also used to identify five paleo-ice-flow directions along the glacial unconformity. These ice flows exhibit polythermal regimes, and four of them are parallel to ice-stream flow sets interpreted from glacial lineations. The integrated interpretation supports localized fault-related basal freezing of the Barents Sea Ice Sheet which resulted in the formation of hill-hole pairs when the ice sheet moved. In this context, the faults functioned as migration pathways for deep thermogenic fluids, possibly sourced from leaking Jurassic reservoirs.This study highlights the importance of the underlying geology for ice-sheet dynamics: While hill-hole pairs above glacial till appear to be commonly associated with dispersed gas hydrates, hill-hole pairs above bedrock additionally indicate a link to underlying fault systems and hydrocarbon reservoirs. Freeze-on of underlying bedrock to the basal ice along the strike of faults in sedimentary bedrock explains deeper hill-hole pairs with smaller extents along the glacial unconformity compared to areally larger but shallow hill-hole pairs detected above glacial till on modern seabeds. Such close association between paleo-thermogenic gas seepage and the location of hill-hole pairs strongly support that hill-hole pairs are excellent markers revealing exit points of fluid migration pathways in petroleum system models.

CAGE21-4 Cruise Report: Oil slicks, gas flares and glacial landforms in Hopendjupet and Sentralbanken

The cruise visited several areas in Hopendjupet, and Sentralbankrenna in the central Barents Sea, and had the following scientific objectives: Surveying and sampling of gas seepage associated with known and assumed sandstone reservoirs sub-cropping at the sea floor due to erosion of overlying cap rocks in Hopendjupet and Sentralbanken Surveying and sampling of gas seepage related to leakage along faults and geological structures breaching the seafloor in Hopendjupet and Sentralbanken Sampling of oil in sea surface slicks and within shallow sediment cores Surveying of landforms associated with the retreat of the Barents Sea Ice Sheet in the outer Sentralbankrenna area The cruise may be known as: CAGE21_4

CAGE21-3 Cruise Report: Ocean bottom seismics and acoustic surveys on the West-Svalbard margin – a study of local seismicity and its effect on methane seepage

Cruise CAGE21-3 with UiT’s research vessel R/V Helmer Hanssen was carried out to address the following objectives within the SEAMSTRESS project (Tectonic stress effects on Arctic methane seepage):1- Recovery of 10 Ocean Bottom Seismometers (OBS) deployed last year north of the Knipovich Ridge-Molloy Transform Fault corner (see report CAGE20-5).2- Conduction of an active source OBS experiment for the study of shear waves propagation in relation to local stress field and focused fluid flow.3- Acquisition of seismic lines for completing a side survey for the FRAME-IODP proposal.In 2020, 10 ocean-bottom seismometers (OBS) were deployed at the northern termination of the Knipovich Ridge to monitor seismic activity. The aim is to detect regional and local earthquakes. If localearthquakes are captured we will investigate the stress field in the region and how faults and fluids react to such stress (Figure 1). From the 10 instruments 8 are from Awi and 2 from UiT. IODP proposal 985 Eastern Fram Strait Palaeo-archive (FRAME) proposed to drill five sites on the western Svalbard margin in order to study chronostratigraphy, palaeoceanography, the palaeoclimatic evolution, and the forcing mechanisms responsible for main climatic transitions and the dynamics of the Svalbard Barents Sea Ice Sheet complex. This cruise acquired additional site survey seismic data for proposed primary and alternate drill sites. The cruise may be known as: CAGE21_3

An updated Weichselian chronostratigraphic framework of the Kongsfjorden Trough Mouth Fan and its implications for the glacial history of Svalbard

The Arctic is a climate‐sensitive area, responding rapidly to present changes, but for the past changes, the record is still incomplete. For instance, the Weichselian glacial history of the Svalbard–Barents Sea Ice Sheet (SBIS) has largely been reconstructed based on studies of the fragmentary Spitsbergen terrestrial and shelf records. However, the sediments removed from the land and shelf areas during peak glacials were deposited on trough mouth fans located along the continental slope. By studying the stratigraphy and processes of the trough mouth fans, comprising a more complete sediment archive, our new data have allowed gaps in the Weichselian glacial history of the SBIS to be refined and filled. Here we present new lithological and geochronological data from the Kongsfjorden Trough Mouth Fan, closely linked to the advance and decay of the SBIS. High‐resolution TOPAS seismic profiles reveal three distinct packages of glacigenic debris flows (GDFs) within its upper stratigraphy, each interpreted to represent an advance of the SBIS to the shelf edge. A radiocarbon dated, 12.6‐m‐long core from the southern flank of the Kongsfjorden Trough Mouth Fan penetrates trough sediments directly linked to the youngest GDF package and terminates in the second GDF, allowing us to study the last two Kongsfjorden ice‐stream advances in greater detail than was previously possible. The age model of core GS10‐164‐09PC, based on combining 14C‐, 18O‐stable isotope and magnetic susceptibility data, spans the last ~54 ka. An Early Weichselian glacial advance is tentatively dated to have ended at ~90 ka. A second peak glaciation is estimated at ~70 ka, followed by a deglaciation from ~54 ka. An ice rafted debris‐rich unit (U7) dated between 38 and 34 ka, followed by a plumite (U6), indicates an advance of unknown extent. The Last Glacial Maximum advance is dated to before 24 ka BP, followed by a rapid deglaciation at ~15 ka. The presence of coarser‐grained sorted sediments at the present seafloor is attributed to the influence of the West‐Spitsbergen Current, acting on water depths of at least 846 m, and is thought to have worked in the vicinity of the coring site since ~14 ka BP.

The marine environmental evolution in the northern Norwegian Sea revealed by foraminifera during the last 60 ka

Both planktonic and benthic foraminifera were identified in a sediment core collected from the northern Norwegian Sea to reconstruct the paleoceanographic evolution since the last glaciation. The assemblages and distribution patterns of dominant foraminiferal species with special habitat preferences indicated that three marine environments occurred in the northern Norwegian Sea since 62 ka BP: (1) an environment controlled by the circulation of the North Atlantic Current (NAC); (2) by polynya-related sinking of brines and upwelling of intermediate water surrounding the polynya; (3) by melt-water from Barents Sea Ice Sheet (BSIS). At 62–52.5 ka BP, a period with the highest summer insolation during the last glaciatial period, intensification of the NAC led to higher absolute abundances and higher diversity of foraminiferal faunas. The higher abundance of benthic species Cibicidoides wuellerstorfi indicates bottom water conditions that were well-ventilated with an adequate food supply; however, higher abundances of polar planktonic foraminiferal species Neogloboquadrina pachyderma (sin.) indicate that the near-surface temperatures were still low. During mid-late MIS 3 (52.5–29 ka BP), the marine environment of the northern Norwegian Sea alternately changed among the above mentioned three environments. At 29–17 ka BP during the last glacial maximum, the dominant benthic species Bolivina arctica from the Arctic Ocean indicates an extreme cold bottom environment. The BSIS expanded to its maximum extent during this period, and vast polynya formed at the edge of the ice sheet. The sinking of brines from the formation of sea ice in the polynyas caused upwelling, indicated by the upwelling adapted planktonic species Globigerinita glutinata. At 17–10 ka BP, the northern Norwegian Sea was controlled by melt-water. With the ablation of BSIS, massive amounts of melt water discharged into the Norwegian Sea, resulting in strong water column stratification, poor ventilation, and an oligotrophic bottom condition, which led to a drastic decline in the abundance and diversity of foraminifera. At 10–0 ka BP, the marine environment was transformed again by the control of the NAC, which continues to modern day. The abrupt decrease in relative abundance of Neogloboquadrina pachyderma (sin.) indicates a rise in near-surface temperature with the strengthening of the NAC and without the influence of the BSIS. Citation : Wang W G, Zhao M W, Yang J C, et al. The marine environmental evolution in the northern Norwegian Sea revealed by foraminifera during the last 60 ka. Adv Polar Sci, 2021, 32(3): 210-220, doi: 10.13679/j.advps.2021.0020

Dynamic and history of methane seepage in the SW Barents Sea: new insights from Leirdjupet Fault Complex

Methane emissions from Arctic continental margins are increasing due to the negative effect of global warming on ice sheet and permafrost stability, but dynamics and timescales of seafloor seepage still remain poorly constrained. Here, we examine sediment cores collected from an active seepage area located between 295 and 353 m water depth in the SW Barents Sea, at Leirdjupet Fault Complex. The geochemical composition of hydrocarbon gas in the sediment indicates a mixture of microbial and thermogenic gas, the latter being sourced from underlying Mesozoic formations. Sediment and carbonate geochemistry reveal a long history of methane emissions that started during Late Weichselian deglaciation after 14.5 cal ka BP. Methane-derived authigenic carbonates precipitated due to local gas hydrate destabilization, in turn triggered by an increasing influx of warm Atlantic water and isostatic rebound linked to the retreat of the Barents Sea Ice Sheet. This study has implications for a better understanding of the dynamic and future evolution of methane seeps in modern analogue systems in Western Antarctica, where the retreat of marine-based ice sheet induced by global warming may cause the release of large amounts of methane from hydrocarbon reservoirs and gas hydrates.

Characterization of a glacial paleo-outburst flood using high-resolution 3-D seismic data: Bjørnelva River Valley, SW Barents Sea

AbstractProglacial braided river systems discharge large volumes of meltwater from ice sheets and transport coarse-grained sediments from the glaciated areas to the oceans. Here, we test the hypothesis if high-energy hydrological events can leave distinctive signatures in the sedimentary record of braided river systems. We characterize the morphology and infer a mode of formation of a 25 km long and 1–3 km wide Early Pleistocene incised valley recently imaged in 3-D seismic data in the Hoop area, SW Barents Sea. The fluvial system, named Bjørnelva River Valley, carved 20 m deep channels into Lower Cretaceous bedrock at a glacial paleo-surface and deposited 28 channel bars along a paleo-slope gradient of ~0.64 m km−1. The landform morphologies and position relative to the paleo-surface support that Bjørnelva River Valley was formed in the proglacial domain of the Barents Sea Ice Sheet. Based on valley width and valley depth, we suggest that Bjørnelva River Valley represents a braided river system fed by violent outburst floods from a glacial lake, with estimated outburst discharges of ~160 000 m3s−1. The morphological configuration of Bjørnelva River Valley can inform geohazard assessments in areas at risk of outburst flooding today and is an analogue for landscapes evolving in areas currently covered by the Greenland and Antarctic ice sheets.

10Be surface exposure dating of the deglaciation of northernmost Norway and Finland

During the Last Glacial Maximum, the coast of Finnmark county, northern Norway, was covered by the Scandinavian Ice Sheet (SIS), which coalesced with the Barents Sea Ice Sheet (BSIS) off the coast. The region is thus important for our understanding of the dynamic interactions between the BSIS and the SIS, yet it remains one of the least dated regions covered by the SIS. To improve the chronological constraints, we present 23 new 10Be ages from eight localities in northernmost Norway and Finland, and discuss implications for the pattern and timing of ice‐sheet retreat in the region. The samples were collected along a 240‐km‐long north–south transect ranging from the outer coast of Nordkinn peninsula (Norway) to Lake Inarijärvi (Finland). The new exposure ages indicate deglaciation of the outer coast at ~14.5 ka. From there, the ice retreated southward until it reached the Main substage moraine complex just north of the Norwegian‐Finnish border during the Younger Dryas. South of the Main substage moraines the deglaciation appears to have become more rapid, eventually reaching Inari, at the southern end of our transect, around 10.4±1.4 ka.

Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions

The Barents Sea Ice Sheet was part of an interconnected complex of ice sheets, collectively referred to as the Eurasian Ice Sheet, which covered north-westernmost Europe, Russia and the Barents Sea during the Last Glacial Maximum (around 21 ky BP). Due to common geological features, the Barents Sea component of this ice complex is seen as a paleo-analogue for the present-day West Antarctic Ice Sheet. Investigating key processes driving the last deglaciation of the Barents Sea Ice Sheet represents an important tool to interpret recent observations in Antarctica over the multi-millennial temporal scale of glaciological changes. We present results from a perturbed physics ensemble of ice sheet model simulations of the last deglaciation of the Barents Sea Ice Sheet, forced with transient atmospheric and oceanic conditions derived from AOGCM simulations. The ensemble of transient simulations is evaluated against the data-based DATED-1 reconstruction to construct minimum, maximum and average deglaciation scenarios. Despite a large model/data mismatch at the western and eastern ice sheet margins, the simulated and DATED-1 deglaciation scenarios agree well on the timing of the deglaciation of the central and northern Barents Sea. We find that the simulated deglaciation of the Barents Sea Ice Sheet is primarily driven by the oceanic forcing, with prescribed eustatic sea level rise amplifying the ice sheet sensitivity to sub-shelf melting over relatively short intervals. Our results highlight that the sub-shelf melting has a very strong control on the simulated grounding-line flux, showing that a slow, gradual ocean warming trend is capable of triggering sustained grounded ice discharge over multi-millennial timescales, even without taking into account marine ice sheet or ice cliff instability.

Abrupt shifts of productivity and sea ice regimes at the western Barents Sea slope from the Last Glacial Maximum to the Bølling-Allerød interstadial

Advanced knowledge of spatio-temporal constraints on the Barents Sea Ice Sheet during the late Weichselian glaciation overshadows relatively limited understanding of seasonal sea ice (experiencing an annual advance-retreat cycle) and primary productivity trends accompanying massive, abrupt climate changes during glacial-deglacial cycles. Such paleo-reconstructions are crucial prerequisites for improved comprehension and prediction of current and future climate change. Here, we investigate sea ice and phytoplankton biomarker distributions in a Barents Sea sediment core covering ca. 25.8–15.4 cal kyr BP to elucidate abrupt shifts of spring–summer sea ice concentrations and relative sympagic–pelagic productivity trends at the southwestern continental slope. Despite significant presence of seasonal sea ice, the Last Glacial Maximum (LGM) and initial shelf edge deglaciation (SEDG) at the core site are characterised by occurrence of productive coastal polynya adjacent to the maximum ice sheet extent. The onset of perennial (i.e. multi-year) ice cover and near-zero productivity during Heinrich Stadial 1 (HS1; ca. 18.0–16.3 cal kyr BP) accompanies significant meltwater fluxes from ice sheet debuttressing and the consequent stagnation of thermohaline circulation. Rapid sea ice retreat and unprecedented pelagic productivity observed after 16.3 cal kyr BP coincides with areal ice sheet deglaciation and is potentially linked to the release of sub-surface heat and nutrient reservoirs, together with reinvigorated deep water circulation following millennial heating of the deep ocean during HS1. We find that a multivariate fingerprinting approach involving assessment of both downcore and surface biomarker distributions is able to distinguish relative ice-algal and pelagic diatom productivity driven by sea ice dynamics.

High-resolution landform assemblage along a buried glacio-erosive surface in the SW Barents Sea revealed by P-Cable 3D seismic data

The Quaternary sedimentary record in the Arctic captures a diverse and evolving range of landscapes reflecting climate changes. Here we study the geological landform assemblage of the Upper Regional Unconformity (URU) in the SW Barents Sea. The aims are (i) to characterize buried geological landforms on a meter-scale resolution, (ii) to understand their link with underlying structures, and (iii) to reconstruct paleo-ice-sheet dynamics and configurations. The data consist of a high-resolution three-dimensional (3D) P-Cable seismic cube with an extent of c. 200 km2 and an inline separation of 6 m. Dominant frequencies of c. 150 Hz allow to image landforms at URU with a vertical resolution of 1–5 m and a horizontal resolution of 3–6 m. We conduct detailed horizon-picking and seismic attribute analysis of the buried URU horizon. We identified four sets of mega-scale glacial lineations, and shear band ridges located to the west of a shear margin moraine. Other characteristic features include hill-hole pairs, transverse ridges, rhombohedral ridges and depressions, iceberg ploughmarks and pockmarks. Polygonal faults below URU and deeper faults have a strong effect on the location of structures observed on URU. Bedrock packages deformed down to 30 m below URU and up to 5 m-high transverse ridges at URU are imprints of glacio-tectonic activity. Deformed strata below URU indicate normal faulting superimposed by glaciotectonic deformation. The four sets of mega-scale glacial lineations indicate four streaming events with thawed glacial beds, with shear band ridges forming in the shearing zone during one of these streaming events. Hill-hole pairs and rhombohedral ridges are frozen-bed features which indicate a polythermal regime at the base of the Barents Sea Ice Sheet during multiple streaming phases. This study therefore shows that paleo-ice streams have been temporarily frozen to the ground in the SW Barents Sea, and that landforms evidencing this freezing are associated with underlying faults.

Late Weichselian glacial history of Forlandsundet, western Svalbard: an inter-ice-stream setting

The last glacial maximum (LGM) and post-glacial Quaternary history of Forlandsundet, the strait between western Spitsbergen and Prins Karls Forland, are enigmatic. Previous terrestrial field studies report contradicting evidence for an ice sheet either overriding the entire strait or completely absent during the LGM. Here, we present a multi-proxy investigation of marine sediments, high-resolution bathymetric data and aerial imagery from Forlandsundet. We reveal glacial till present at 15 cal. ka BP and geomorphological landforms characteristic to an inter-ice-stream glaciated margin. This new evidence implies that the Forlandsundet region was fully glaciated during the LGM. This glaciation was followed by a stepwise retreat of glacial ice during the Bolling–Allerod (14.7–12.7 cal. ka BP) and Younger Dryas (12.7–11.7 cal. ka BP). The Holocene record from the marine sediments is incomplete, with a hiatus from approximately 11.8 to 7.4 cal. ka BP, interpreted as an erosive event. By the mid-Holocene (7.4 cal. ka BP), more temperate, Atlantic conditions based on the benthic foraminiferal assemblages prevailed, and are followed by gradual cooling into the late Holocene (< 4 cal. ka BP). This study provides new data to resolve the LGM extent of the Svalbard–Barents Sea ice sheet in the Forlandsundet region and sheds light on the deglacial ice dynamics in a palaeo-inter-ice-stream area driven by the inflow of warm Atlantic water.

Ice‐rafting patterns on the western Svalbard slope 74–0 ka: interplay between ice‐sheet activity, climate and ocean circulation

The distribution of ice‐rafted detritus (IRD) is studied in three cores from the western Svalbard slope (1130–1880 m water depth, 76–78°N) covering the period 74–0 ka. The aim was to provide new insight into the dynamics of the Svalbard–Barents Sea Ice Sheet during Marine Isotope Stages (MIS) 4–1 to get a better understanding of ice‐sheet interactions with changes in ocean circulation and climate on orbital and millennial (Dansgaard–Oeschger events of stadial–interstadial) time scales. The results show that concentration, flux, composition and grain‐size of IRD vary with climate and ocean temperature on both orbital and millennial time scales. The IRD consists mainly of fragments of siltstones and mono‐crystalline transparent quartz (referred to as ‘quartz’). IRD dominated by siltstones has a local Svalbard–Barents Sea source, while IRD dominated by quartz is from distant sources. Local siltstone‐rich IRD predominates in warmer climatic phases (interstadials), while the proportion of allochthonous quartz‐rich IRD increases in cold phases (glacials and stadials/Heinrich events). During the Last Glacial Maximum and early deglaciation at 24–16.1 ka, the quartz content reached up to &gt;90%. In warm climate, local iceberg calving apparently increased and the warmer ocean surface caused faster melting. During the glacial maxima (MIS 4 and MIS 2) and during cold stadials and Heinrich events, the local ice‐sheets must have been relatively stable with low ablation. During ice retreat phases of the MIS 4/3 and MIS 2/1 transitions, maxima in IRD deposition were dominated by local coarse‐grained IRD. These maxima correlate with episodes of climate warming, indicating a rapid, stepwise retreat of the Svalbard–Barents Sea Ice Sheet in phase with millennial‐scale climate oscillations.

Subglacial water storage and drainage beneath the Fennoscandian and Barents Sea ice sheets

Subglacial hydrology modulates how ice sheets flow, respond to climate, and deliver meltwater, sediment and nutrients to proglacial and marine environments. Here, we investigate the development of subglacial lakes and drainage networks beneath the Fennoscandian and Barents Sea ice sheets over the Late Weichselian. Utilizing an established coupled climate/ice flow model, we calculate high-resolution, spatio-temporal changes in subglacial hydraulic potential from ice sheet build-up (∼37 ka BP) to complete deglaciation (∼10 ka BP). Our analysis predicts up to 3500 potential subglacial lakes, the largest of which was 658 km2, and over 70% of which had surface areas <10 km2, comparable with subglacial lake-size distributions beneath the Antarctic Ice Sheet. Asynchronous evolution of the Fennoscandian Ice Sheet into the flatter relief of northeast Europe affected patterns of subglacial drainage, with up to 100 km3 more water impounded within subglacial lakes during ice build-up compared to retreat. Furthermore, we observe frequent fill/drain cycles within clusters of subglacial lakes at the onset zones and margins of ice streams that would have affected their dynamics. Our results resonate with mapping of large subglacial channel networks indicative of high-discharge meltwater drainage through the Gulf of Bothnia and central Barents Sea. By tracking the migration of meltwater drainage outlets during deglaciation, we constrain locations most susceptible to focussed discharge, including the western continental shelf-break where subglacial sediment delivery led to the development of major trough-mouth fans. Maps of hydraulic potential minima that persist throughout the Late Weichselian reveal potential sites for preserved subglacial lake sediments, thereby defining useful targets for further field-investigation.

Paleoceanography of northeastern Fram Strait since the last glacial maximum: Palynological evidence of large amplitude changes

Sea-surface conditions in northeastern Fram Strait since the last glacial maximum (LGM) were reconstructed from cores MSM5/5-712-2 and PS2863/1–2 based on palynological assemblages, ecological preferences of dinocysts and application of the modern analog technique. Dinocyst in LGM sediments are sparse, but their assemblages reflect mild summer conditions. Given the regional context and evidence from other tracers, the dinocyst assemblages of the LGM could relate to regional fluxes of dinocysts during exceptional mild summers. From 19 to 14.7 ka, dinocyst data suggest very cold conditions with extensive sea-ice cover, while abundant reworked palynomorphs indicate intense glacial erosion. An abrupt transition at 14.7–14.5 ka was marked by a peak in summer temperatures coinciding with a rapidly deposited sediment layer related to a regional meltwater plume event in western Svalbard. From 14.7 to 12.6 ka, large seasonal temperature contrasts with mild summers and cold winters together with low salinity indicate continuous melting of the Svalbard Barents Sea ice sheet fostered by warm climate. At 12.6 ka, the regional onset of the Younger Dryas was marked by cooling and increased salinity. On a regional scale, the 12.6–12 ka interval corresponds to an important transition involving enhanced circulation of Arctic waters around Svalbard and establishment of coastal fronts along its northern and western margins. Modern-like oceanic conditions with relatively high salinity and low seasonal temperature contrast developed at about 7.6 ka. Since then, a slight cooling is observed, especially in winter. This study offers a comprehensive picture of the deglacial phases in eastern Fram Strait with unique data on the sea-surface salinity, which controls surface water stratification and plays an important role in ocean circulation.

A 190-ka biomarker record revealing interactions between sea ice, Atlantic Water inflow and ice sheet activity in eastern Fram Strait

The northeastern Fram Strait at the entrance to the Arctic Ocean represents a key observatory for sea ice reconstructions as it sensitively reacts to environmental changes. A combined biomarker approach (HBIs, sterols, alkenones) was carried out on Core PS93/006-1 from the western Svalbard margin to reconstruct sea ice conditions related to glacial–interglacial cycles of the last 190 ka. The continuous presence of sea ice demonstrates the strong influence of polar water masses in the eastern Fram Strait. Glacial intervals are characterised by extended sea ice conditions with perennial sea ice cover during early MIS 6, the Penultimate Glacial Maximum, the interstadial MIS 5d, MIS 4 and the Last Glacial Maximum. Less severe, yet highly variable, sea ice conditions with more frequent summer melt dominated the interglacial stages. The opposing sea ice conditions along the western and northern Svalbard margin highlight the different regional impact of various environmental forces in eastern Fram Strait. Thus, the major expansion of the Svalbard Barents Sea Ice Sheet favoured the formation of perennial sea ice west of Svalbard while it triggered the establishment of marginal ice cover on the Yermak Plateau.