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The main goal of CAGE 17-2 AMGG cruise was to study the gas-hydrate-bearing system and methane emission off south and east of Spitsbergen in Storfjordrenna and the northern flank of Olga Basin (named here Olga craters) respectively, and in the West Sentralbanken. We addressed this through a comprehensive scientific program comprising dives with the MISO-Tow Cam adapted to the multicorer frame from UiT-NPI (TowCam/Multicorer, TCM), methane measurements in sediments, water column, and in air, sediment coring (multicorer + gravity corer), water column and sediment biogeochemistry, microbiology, micropaleontology, and bathymetric mapping. Cruise CAGE 17-2 was also hosting this year’s AMGG research school cruise with masters, PhD and post-doc students participating. The areas investigated were: Storfjordrenna, Pingos site (ca 380 m water depth),Northern Flank of Olga Basin (ca 140 m water depth)West Sentralbanken (ca 200 m water depth) We planned the following activities during the CAGE 17-2 cruise: EM 302 Simrad swath bathymetry mapping to identify seabed morphology Mapping of flare distributionsCTD stations at different water depths and in different areas for measurements ofocean water masses characteristics, andwater sampling for water/gas chemistry and microbiology investigations across methane seeps.TCM surveys (video-camera) to image seabed fluid flow expressions, sites of bacteria mats, crusts and gas bubbles.Repeated deployments with TCM to sample surficial and shallow sediments with respect to microbiology, geochemistry, biogeochemistry, and micropaleontology.Gravity corer for studying sediment biogeochemistry, biomarkers, microbiology, and foraminifera.Scrape sampling to collect rocks and crusts.Gas Chromatographer (GC) to measure methane concentration in the water and sediment samples.Flasks Restek, Electro-Polished Miniature Canister (1000 cc) for air samples. Part of the cruise was supported by NPD, Oljedirektoratet. Special thanks to Rune Mattingsdal, NPD. The cruise may be known as: CAGE17_2

The research cruise was part of the Centre of Excellence (SFF) Centre for Arctic Gas Hydrate Environment and Climate (CAGE) at UiT – The Arctic University of Norway. It was partly supported by The Norwegian Petroleum Directorate. From Tromsø, we visited Sentralbankrenna and Hopendjupet in the central Barents Sea in order to pursue the following scientific objectives: – Identify gas seepage associated with known and assumed sandstone reservoirs sub-cropping at the sea floor. – Identify gas seepage related to leakage along faults and geological structures breaching the seafloor. – Collect gravity cores, multibeam and sub-bottom data to establish how grounding zone processes impact marine-based ice sheet behaviour and trigger ice-stream retreat during deglaciation. The cruise may be known as: CAGE20_2

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

Uplift and erosion are complex phenomena in terms of their governing processes, precise timing and exact magnitude. The intricate relationship between different geodynamic processes leading to uplift may increase uncertainties in estimating spatial and temporal patterns. Sediment distribution from uplifted (and eroded) topography and the corresponding paleoenvironmental reconstructions require reliable constrains. The Barents Shelf provides a unique arena to study uplift and erosion due to extensive seismic and well data attributed to high petroleum activity. This particular interest has led to a voluminous literature about this topic over the last three decades. Here, we present the current status of the Cenozoic uplift and erosion on the Norwegian Barents Shelf by reviewing the key terminology, its tectonic history and paleoenvironment, methods in quantifying uplift and erosion, as well as timing and possible mechanisms. Our new erosion maps show an increase in net erosion to the north and northeast that represents key underlying concepts, including tectonic (compression, rift-flank uplift, thermo-mechanical coupling, mantle dynamics, flexural/isostatic response) as well as magmatic and glacial processes. We have integrated pre-glacial and glacial net erosion using the mass balance method and added our results from sonic velocity, interval velocity and sandstone diagenesis methods to the new maps. This review shows that discrepancies of net erosion estimates from different methods are on the order of 500 m. Finally, we identify research gaps for future studies, with implications for the Barents Shelf and other uplifted basins worldwide This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The dynamics and paleo‐glaciology of ice sheet interiors during the last deglaciation are poorly constrained, hindering ice sheet model reconstructions. We provide direct evidence of Fennoscandian Ice Sheet (FIS) interior behavior during deglaciation through surface exposure dating. Our results demonstrate early thinning of the FIS, prior to the Younger Dryas (YD, 12.8–11.7 ka). Interior thinning in central Norway was concurrent with retreat along the coastline, exposing ice‐free mountainous tracts, potentially as early as 20–15 ka. The FIS then formed moraines in these ice‐free tracts during the YD. This is contrary to current hypotheses advocating a landscape fully covered by cold, inactive ice during this period. Present empirical and model reconstructions fail to capture rapid interior downwastage, increasing uncertainties in ice sheet volume estimates and sea level contributions. Plain language summary The decay of past ice sheets provides an analogue for the retreat of present‐day ice sheets, due to rapidly changing climate conditions experienced then and now. One limitation with ice reconstructions is, however, that they rarely contain dated evidence for how the ice sheet interiors behaved during their termination. In a new reconstruction of the geometry of the southern part of the Fennoscandian Ice Sheet (FIS), we overcome this limitation. We document that areas at the heart of the southern ice dome, previously thought to be consumed by thick ice, were in fact ice‐free 12,000 years ago suggesting that the FIS was considerably thinner than thought and that previous estimates of the ice sheet’s volume need to be recalculated.

Iceland’s periglacial realm is one of the most dynamic on the planet, with active geomorphological processes and high weathering rates of young bedrock resulting in high sediment yields and ongoing mass movement. Permafrost is discontinuous in Iceland’s highlands and mountains over c. 800 m a.s.l, and sporadic in palsa mires in the central highlands. During the late Pleistocene and Holocene, Iceland’s periglacial environment varied considerably in time and space, dominated by glacial fluctuations and periglacial processes. To evaluate the dynamics of permafrost in Iceland since the last deglaciation, we use the output of a coupled climate/ice sheet model to force a transient permafrost model (CryoGRID 2) from the Last Glacial Maximum (LGM) through to the present. We find that permafrost was widespread across the deglaciated areas of western, northern and eastern Iceland after the LGM, and that up to 20% of Iceland’s terrestrial area was underlain by permafrost throughout the late Pleistocene. This influenced geomorphological processes and landform generation: the early collapse of the marine-based ice sheet together with the aggradation of permafrost in these zones initiated the formation of abundant and now relict rock glaciers across coastal margins. Permafrost degraded rapidly after the Younger Dryas, with a marked impact on slope stability. Permafrost that formed during the Little Ice Age is again thawing rapidly, and an escalation in slope failure and mass-movement might be currently underway. Our study demonstrates that large regions of Iceland have been underlain by permafrost for millennia, facilitating landform development and influencing the stability of steep slopes.

Accepted manuscript version. Published version available at https://doi.org/10.1016/j.quascirev.2018.10.007. Licensed CC BY-NC-ND 4.0. 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

Warm, subtropical-originating Atlantic water (AW) has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet (GrIS), yet the specific processes by which this water mass interacts with and erodes the calving front of tidewater glaciers is frequently modelled and much speculated upon but remains largely unobserved. We present a suite of fjord salinity, temperature, turbidity versus depth casts along with glacial runoff estimation from Rink and Store glaciers, two major marine outlets draining the western sector of the GrIS during 2009 and 2010. We characterise the main water bodies present and interpret their interaction with their respective calving fronts. We identify two distinct processes of ice–ocean interaction which have distinct spatial and temporal footprints: (1) homogenous free convective melting which occurs across the calving front where AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water which occurs at distinct injection points across the calving front. Throughout the study, AW at 2.8 ± 0.2 °C was consistently observed in contact with both glaciers below 450 m depth, yielding homogenous, free convective submarine melting up to ~200 m depth. Above this bottom layer, multiple interactions are identified, primarily controlled by the rate of subglacial fresh-water discharge which results in localised and discrete upwelling plumes. In the record melt year of 2010, the Store Glacier calving face was dominated by these runoff-driven plumes which led to a highly crenulated frontal geometry characterised by large embayments at the subglacial portals separated by headlands which are dominated by calving. Rink Glacier, which is significantly deeper than Store has a larger proportion of its submerged calving face exposed to AW, which results in a uniform, relatively flat overall frontal geometry.

Understanding the retreat behaviour of past marine-ice sheets provides vital context to accurate assessment of the present stability and long-term response of contemporary polar-ice sheets to climate and oceanic warming. Here new multibeam swath-bathymetry data and sedimentological analysis are combined with high resolution ice-sheet modelling to reveal complex landform assemblages and process-dynamics associated with deglaciation of the British-Celtic Ice Sheet (BCIS) within the Irish Sea Basin. Our reconstruction indicates a non-linear relationship between the rapidly receding Irish Sea Ice Stream, the largest draining the BCIS, and the retreat of outlet glaciers draining the adjacent, terrestrially based ice sheet centred over Wales. Retreat of Welsh ice was episodic; superimposed over low-order oscillations of its margin are asynchronous outlet re-advances driven by catchment-wide mass balance variations that are amplified through migration of the ice cap's main ice-divide. Formation of large, linear ridges which extend at least 12.5 km offshore (locally known as sarns) and dominate the regional bathymetry are attributed to repeated frontal and medial morainic deposition associated with the re-advancing phases of these outlet glaciers. Our study provides new insight into ice-sheet extent, dynamics and non-linear retreat across a major palaeo-ice stream confluence zone, and has ramifications for the interpretation of recent fluctuations observed by satellites over short-time scales across marine-sectors of the Greenland and Antarctic ice sheets.

Accepted manuscript version. Published version available at https://doi.org/10.1016/j.earscirev.2017.02.001. Accepted manuscript version, licensed CC BY-NC-ND 4.0. The fragmentary glacial-geological record across the Icelandic continental shelf has hampered reconstruction of the volume, extent and chronology of the Late Weichselian ice sheet particularly in key offshore zones. Marine geophysical data collected over the last two decades reveal that the ice sheet likely attained a continental shelf-break position in all sectors during the Last Glacial Maximum, though its precise timing and configuration remains largely unknown. Within this context, we review the available empirical evidence and use a well-constrained three-dimensional thermomechanical model to investigate the drivers of an extensive Late Weichselian Icelandic ice-sheet, its sensitivity to environmental forcing, and phases of deglaciation. Our reconstruction attains the continental shelf break across all sectors with a total ice volume of 5.96 × 105 km3 with high precipitation rates being critical to forcing extensive ice sheet flow offshore. Due to its location astride an active mantle plume, a relatively fast and dynamic ice sheet with a low aspect ratio is maintained. Our results reveal that once initial ice-sheet retreat was triggered through climate warming at 21.8 ka BP, marine deglaciation was rapid and accomplished in all sectors within c. 5 ka at a mean rate of 71 Gt of mass loss per year. This rate of ice wastage is comparable to contemporary rates observed for the West Antarctic ice sheet. The ice sheet subsequently stabilised on shallow pinning points across the near shelf for two millennia, but abrupt atmospheric warming during the Bølling Interstadial forced a second, dramatic collapse of the ice sheet onshore with a net wastage of 221 Gt a−1 over 750 years, analogous to contemporary Greenland rates of mass loss. Geothermal conditions impart a significant control on the ice sheet's transient response, particularly during phases of rapid retreat. Insights from this study suggests that large sectors of contemporary ice sheets overlying geothermally active regions, such as Siple Coast, Antarctica, and NE Greenland, have the potential to experience rapid phases of mass loss and deglaciation once initial retreat is initiated.

The Eurasian ice sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea-level lowering. Whilst recent terrestrial and marine empirical insights have improved understanding of the chronology, pattern and rates of retreat of this vast ice sheet, a concerted attempt to model the deglaciation of the EISC honouring these new constraints is conspicuously lacking. Here, we apply a first-order, thermomechanical ice sheet model, validated against a diverse suite of empirical data, to investigate the retreat of the EISC after 23 ka BP, directly extending the work of Patton et al. (2016) who modelled the build-up to its maximum extent. Retreat of the ice sheet complex was highly asynchronous, reflecting contrasting regional sensitivities to climate forcing, oceanic influence, and internal dynamics. Most rapid retreat was experienced across the Barents Sea sector after 17.8 ka BP when this marine-based ice sheet disintegrated at a rate of ∼670 gigatonnes per year (Gt a−1) through enhanced calving and interior dynamic thinning, driven by oceanic/atmospheric warming and exacerbated by eustatic sea-level rise. From 14.9 to 12.9 ka BP the EISC lost on average 750 Gt a−1, peaking at rates >3000 Gt a−1, roughly equally partitioned between surface melt and dynamic losses, and potentially contributing up to 2.5 m to global sea-level rise during Meltwater Pulse 1A. Independent glacio-isostatic modelling constrained by an extensive inventory of relative sea-level change corroborates our ice sheet loading history of the Barents Sea sector. Subglacial conditions were predominately temperate during deglaciation, with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network. Moreover, the maximum EISC and its isostatic footprint had a profound impact on the proglacial hydrological network, forming the Fleuve Manche mega-catchment which had an area of ∼2.5 × 106 km2 and drained the present day Vistula, Elbe, Rhine and Thames rivers through the Seine Estuary. During the Bølling/Allerød oscillation after c. 14.6 ka BP, two major proglacial lakes formed in the Baltic and White seas, buffering meltwater pulses from eastern Fennoscandia through to the Younger Dryas when these massive proglacial freshwater lakes flooded into the North Atlantic Ocean. Deglaciation temporarily abated during the Younger Dryas stadial at 12.9 ka BP, when remnant ice across Svalbard, Franz Josef Land, Novaya Zemlya, Fennoscandia and Scotland experienced a short-lived but dynamic re-advance. The final stage of deglaciation converged on present day ice cover around the Scandes mountains and the Barents Sea by 8.7 ka BP, although the phase-lagged isostatic recovery still continues today.

Source at: http://doi.org/10.1073/pnas.1619288114 Seafloor methane release due to the thermal dissociation of gas hydrates is pervasive across the continental margins of the Arctic Ocean. Furthermore, there is increasing awareness that shallow hydrate-related methane seeps have appeared due to enhanced warming of Arctic Ocean bottom water during the last century. Although it has been argued that a gas hydrate gun could trigger abrupt climate change, the processes and rates of subsurface/ atmospheric natural gas exchange remain uncertain. Here we investigate the dynamics between gas hydrate stability and environmental changes from the height of the last glaciation through to the present day. Using geophysical observations from offshore Svalbard to constrain a coupled ice sheet/gas hydrate model, we identify distinct phases of subglacial methane sequestration and subsequent release on ice sheet retreat that led to the formation of a suite of seafloor domes. Reconstructing the evolution of this dome field, we find that incursions of warm Atlantic bottom water forced rapid gas hydrate dissociation and enhanced methane emissions during the penultimate Heinrich event, the Bølling and Allerød interstadials, and the Holocene optimum. Our results highlight the complex interplay between the cryosphere, geosphere, and atmosphere over the last 30,000 y that led to extensive changes in subseafloor carbon storage that forced distinct episodes of methane release due to natural climate variability well before recent anthropogenic warming.

Published version at http://doi.org/10.1016/j.quascirev.2016.07.012. License CC BY-NC-ND 4.0. Glacier bed overdeepenings are ubiquitous in glacier systems and likely exert significant influence on ice dynamics, subglacial hydrology, and ice stability. Understanding of overdeepening formation and evolution has been hampered by an absence of quantitative empirical studies of their distribution and morphology, with process insights having been drawn largely from theoretical or numerical studies. To address this shortcoming, we first map the distribution of potential overdeepenings beneath the Antarctic and Greenland ice sheets using a GIS-based algorithm that identifies closed-contours in the bed topography and then describe and analyse the characteristics and metrics of a subset of overdeepenings that pass further quality control criteria. Overdeepenings are found to be widespread, but are particularly associated with areas of topographically laterally constrained ice flow, notably near the ice sheet margins where outlet systems follow deeply incised troughs. Overdeepenings also occur in regions of topographically unconstrained ice flow (for example, beneath the Siple Coast ice streams and on the Greenland continental shelf). Metrics indicate that overdeepening growth is generally allometric and that topographic confinement of ice flow in general enhances overdeepening depth. However, overdeepening depth is skewed towards shallow values – typically 200–300 m – indicating that the rate of deepening slows with overdeepening age. This is reflected in a decline in adverse slope steepness with increasing overdeepening planform size. Finally, overdeepening long-profiles are found to support headward quarrying as the primary factor in overdeepening development. These observations support proposed negative feedbacks related to hydrology and sediment transport that stabilise overdeepening growth through sedimentation on the adverse slope but permit continued overdeepening planform enlargement by processes of headward erosion.

Published version, source at http://doi.org/10.1016/j.quascirev.2016.10.009. License CC BY-NC-ND 4.0. The Eurasian ice-sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum (LGM), after the Antarctic and North American ice sheets. Despite its global significance, a comprehensive account of its evolution from independent nucleation centres to its maximum extent is conspicuously lacking. Here, a first-order, thermomechanical model, robustly constrained by empirical evidence, is used to investigate the dynamics of the EISC throughout its build-up to its maximum configuration. The ice flow model is coupled to a reference climate and applied at 10 km spatial resolution across a domain that includes the three main spreading centres of the Celtic, Fennoscandian and Barents Sea ice sheets. The model is forced with the NGRIP palaeo-isotope curve from 37 ka BP onwards and model skill is assessed against collated flowsets, marginal moraines, exposure ages and relative sea-level history. The evolution of the EISC to its LGM configuration was complex and asynchronous; the western, maritime margins of the Fennoscandian and Celtic ice sheets responded rapidly and advanced across their continental shelves by 29 ka BP, yet the maximum aerial extent (5.48 × 106 km2) and volume (7.18 × 106 km3) of the ice complex was attained some 6 ka later at c. 22.7 ka BP. This maximum stand was short-lived as the North Sea and Atlantic margins were already in retreat whilst eastern margins were still advancing up until c. 20 ka BP. High rates of basal erosion are modelled beneath ice streams and outlet glaciers draining the Celtic and Fennoscandian ice sheets with extensive preservation elsewhere due to frozen subglacial conditions, including much of the Barents and Kara seas. Here, and elsewhere across the Norwegian shelf and North Sea, high pressure subglacial conditions would have promoted localised gas hydrate formation.

Accepted manuscript version. Published version available in Quaternary Science Reviews (2016) 147, p.122-135. The 3D geometrical evolution of the Barents Sea Ice Sheet (BSIS), particularly during its late-glacial retreat phase, remains largely ambiguous due to the paucity of direct marine- and terrestrial-based evidence constraining its horizontal and vertical extent and chronology. One way of validating the numerous BSIS reconstructions previously proposed is to collate and apply them under a wide range of Earth models and to compare prognostic (isostatic) output through time with known relative sea-level (RSL) data. Here we compare six contrasting BSIS load scenarios via a spherical Earth system model and derive a best-fit, χ2 parameter using RSL data from the four main terrestrial regions within the domain: Svalbard, Franz Josef Land, Novaya Zemlya and northern Norway. Poor χ2 values allow two load scenarios to be dismissed, leaving four that agree well with RSL observations. The remaining four scenarios optimally fit the RSL data when combined with Earth models that have an upper mantle viscosity of 0.2–2 × 1021 Pa s, while there is less sensitivity to the lithosphere thickness (ranging from 71 to 120 km) and lower mantle viscosity (spanning 1–50 × 1021 Pa s). GPS observations are also compared with predictions of present-day uplift across the Barents Sea. Key locations where relative sea-level and GPS data would prove critical in constraining future ice-sheet modelling efforts are also identified.