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Accepted manuscript version, licensed CC BY-NC-ND 4.0. The Barents Sea has experienced intense erosion throughout the Cenozoic due to uplift and repeated episodes of glaciation. This, in turn, has driven large pressure and temperature fluctuations in the sediment substrate along with rearrangement of thermogenic oil and gas accumulations. As a result, some hydrocarbon fields have relatively shallow depths, and natural gas release is widespread. This study focuses on the process of hydrocarbon leakage from the Realgrunnen reservoir - encompassing the Hanssen and Wisting discoveries - to the shallow subsurface caused by repeated cycles of glacial erosion in the central Barents Sea throughout the Quaternary. We apply 2D basin and petroleum system modeling to two seismic sections using data from two wells and run ten different scenarios that test model sensitivity to key parameters. We find that the primary factors governing gas leakage are the erosion amount, its distribution between glacial and preglacial stages, and the timing of the glaciations. Our results demonstrate that intense oil and gas leakage from the Realgrunnen reservoir occurs primarily through widespread faults activated during the first deglaciation episode. Further considerable gas leakage occurs by the seal breach after a critical overburden thickness is eroded and pressure on the reservoir decreases to ca. 9 MPa. Modeling reveals that the first deglaciation episode causes up to ca. 20% loss of oil and gas from the reservoir, whereas leakage after the seal breach yields a further ca. 15% decrease in gas. Our results are supported by seismic analyses that demonstrate hydrocarbon leakage in the study area

Accepted manuscript version, licensed CC BY-NC-ND 4.0. Abrasion and quarrying are significant processes of subglacial erosion for ice masses in direct contact with hard substrates, yet their relative efficacy and spatio-temporal variability is unclear. Here, we investigate the glacial impact of these processes on a 70 m by 60 m bedrock surface at Moel Ysgyfarnogod in the Rhinog Mountains, Wales, using a combination of high-resolution digital photographs, analysis of a Digital Terrain Model derived from an Unmanned Aerial Vehicle survey, and regional ice sheet modelling. We map and analyze the distribution of grooved and striated surfaces, abraded surfaces, quarried blocks and open fractures in addition to the orientation of pre-existing bedrock fractures and joints. The grooves and striations are orientated in a single, consistent direction across the bedrock surfaces related to regional ice flow during the Late Pleistocene. Abraded and smoothed bedrock dominates the proximal edges of the bedrock outcrop and quarrying prevails on the distal edges of the bedrock outcrop, which are dominated by detached and partially detached blocks. We propose these blocks were removed during the final stages of the last glacial cycle when subglacial meltwater was plentiful in this otherwise predominantly frozen subglacial setting. A minimum estimate of 2000 m3 displaced material at this site implies that subglacial quarrying would have been an important erosional process during final stages of deglaciation.

We present results from a suite of forward transient numerical modelling experiments of the British and Irish Ice Sheet (BIIS), consisting of Scottish, Welsh and Irish accumulation centres, spanning the last Glacial period from 38 to 10 ka BP. The 3D thermomechanical model employed uses higher-order physics to solve longitudinal (membrane) stresses and to reproduce grounding-line dynamics. Surface mass balance is derived using a distributed degree-day calculation based on a reference climatology from mean (1961–1990) precipitation and temperature patterns. The model is perturbed from this reference state by a scaled NGRIP oxygen isotope curve and the SPECMAP sea-level reconstruction. Isostatic response to ice loading is computed using an elastic lithosphere/relaxed asthenosphere scheme. A suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities, to yield a subset of experiments that showed close correspondence to offshore and onshore ice-directional indicators, broad BIIS chronology, and the relative sea-level record. Three of these simulations are described in further detail and indicate that the separate ice centres of the modelled BIIS complex are dynamically interdependent during the build up to maximum conditions, but remain largely independent throughout much of the simulation. The modelled BIIS is extremely dynamic, drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time-scale. A series of binge/purge, advance/retreat, cycles are identified which correspond to alternating periods of relatively cold-based ice, (associated with a high aspect ratio and net growth), and wet-based ice with a lower aspect ratio, characterised by streaming. The timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling, but are modulated and phase-lagged to the oscillations within the NGRIP record of climate forcing. Phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate, resulting in major iceberg/melt discharge events into the North Sea and Atlantic Ocean. The broad chronology of the modelled BIIS indicates a maximum extent at 20 ka, with fast-flowing ice across its western and northern sectors that extended to the continental shelf edge. Fast-flowing streams also dominate the Irish Sea and North Sea Basin sectors and impinge onto SW England and East Anglia. From 19 ka BP deglaciation is achieved in less than 2000 years, discharging the freshwater equivalent of 2 m global sea-level rise. A much reduced ice sheet centred on Scotland undergoes subsequent retrenchment and a series of advance/retreat cycles into the North Sea Basin from 17 ka onwards, culminating in a sustained Younger Dryas event from 13 to 11.5 ka BP. Modelled ice cover is persistent across the Western and Central Highlands until the last remnant glaciers disappear around 10.5 ka BP.

This paper provides the first comprehensive description and interpretation of Late Devensian glacigenic deposits exposed in a 2 km-long cliff section at Tonfanau, Mid-West Wales. The section offers crucial insight concerning glacier dynamics and sedimentation on the eastern margin of the Irish Sea Basin. Six lithofacies are identified: diamicton, sandy gravel, well-rounded gravel, well-sorted sand, muddy sand, and laminites. Two diamicton horizons are present: an upper brown clast-rich sandy diamicton, and a lower grey clast-poor muddy diamicton, the latter being only sporadically exposed by wave action. Sand and gravel occur in close association, as well as minor mud and gravel successions. The sedimentary succession at Tonfanau records the dynamics and deposition of both Welsh and Irish Sea Ice. The lowermost part of the exposed section records Welsh ice extending into Cardigan Bay, depositing a diamicton originating from the adjacent hinterland to the West. As the Irish Sea Ice Stream flowed south, it impinged upon the present coastline at Tonfanau, depositing sediment with a northern provenance on top of predominantly Welsh material, as indicated by clasts from the Irish Sea Basin, Anglesey and the Llŷn Peninsula. The depositional environment for the Irish Sea materials is interpreted as one where a fluctuating ice margin generated a grounding-line fan complex in an ice-contact lake that merged laterally with lake sediments derived from suspension and turbidity currents. Succeeding facies indicate over-riding by Irish Sea Ice. Finally, the upper few metres of the succession was subjected to cryoturbation under a periglacial climate.