Quaternary Ice Sheets Research Articles

Periglacial landforms and landscape development in southern England

The south-central and south-east England Geological Conservation Review region is unique in Britain in lying completely outside the margins of Quaternary ice sheets. In view of this, the area has been described as a ‘relict periglacial landscape’. This implies that the region has evolved its current form substantially under the influence of seasonal and/or perennial frost. In fact, modern research has demonstrated that permafrost, either continuous or discontinuous, likely existed across probably the whole of the region at different times during the Quaternary. This has important implications for ground permeability and the strength of sediments and soils and this has, without doubt, influenced landscape development. Whilst the whole region appears to have experienced cold environmental conditions, the landforms, structures and sediments of some sites are particularly associated with periglacial processes. Allington Quarry, Spot Lane Quarry, Oaken Wood, Chiddingly Wood (known locally as Chiddinglye Wood), High Rocks and Rusthall Common have exhibited typical cambering structures with open or closed gulls. The latter three sites also display a fine range of surface weathering features. Hubbard's Hill is characterised by solifluction and active-layer detachment slides and associated subsurface shear structures, whilst the sarsen trains at Fyfield Down and Valley of Stones are also attributed to solifluction processes. Birling Gap and Pegwell Bay exhibit spectacular sediment brecciation and involutions. Pegwell Bay is also known for its thick layer of periglacial loess, a sediment that is also a feature of North Cliff, Broadstairs. Unfortunately, the dating of these landscape features has, so far, proved possible only at Hubbard's Hill and Pegwell Bay. Nevertheless, the sites reviewed here provide exceptional, and in some cases internationally important, indications of landscape development in cold, often permafrost, environments which justifies their status as GCR sites.

Revisiting the timing of Saginaw lobe ice retreat and implications for drainage adjustments across southern Michigan, USA

Understanding the behavior of paleo-ice sheets in response to past climate change and land surface processes can provide insights into the interplay between the atmosphere, ocean surface, and the cryosphere, which helps update current climate models and understand landscape evolution. The timing of the advancement and retreat of ice lobes along Quaternary ice sheet margins and their link to ocean surface temperature fluctuation are of particular interest. The Saginaw lobe along the southern margin of the Laurentide Ice Sheet (LIS) was bound by the Lake Michigan and Huron-Erie lobes. It flowed out of Saginaw Bay, across Lower Michigan, and into northern Indiana. All three of these lobes retreated across the region asynchronously, with the Saginaw lobe retreating first. The asynchronous behavior of the lobes allowed the Lake Michigan and Huron-Erie lobes to overprint and alter landscapes once occupied by Saginaw lobe ice.Lacustrine sediments within the Sturgis Moraine, deposited during the Saginaw lobe retreat in extreme southwestern Michigan, yielded optically stimulated luminescence (OSL) ages of 30.1 ± 1.8, 28.7 ± 1.5 and 25.2 ± 1.9 ka. An additional radiocarbon date (22.22 ± 0.8 cal ka) was measured from bryophytes sampled near the base of an ice-walled lake plain atop the moraine. These dates indicate that deglaciation of the Saginaw lobe could have been underway in southwestern Michigan between ∼ 30 and 22 ka, while ice margins of the Huron-Erie and Lake Michigan lobes were further south in Indiana and Illinois. The new dates indicate that southwestern Michigan may have witnessed ice-free conditions four thousand years earlier than previously thought. Moreover, the paleo-hydrological analyses of southwestern Michigan using detailed surficial geology mapping, Lidar-based longitudinal and terrace profiles along meltwater channels, and OSL data indicate that meltwater originating from the Saginaw—Huron-Erie interlobate area drained westward across the Saginaw lobe terrain between ∼ 18.0 to 14.6 Ka ago. The findings call for revisiting the current understanding of the timing and behavior of the southern margins of the LIS and the Holocene landscape evolution in Michigan.

Eurasian Ice Sheet derived meltwater pulses and their role in driving atmospheric dust activity: Late Quaternary loess sources in SE England

The role of Quaternary ice sheet fluctuations in driving meltwater pulses and ocean circulation perturbations is widely acknowledged. What is less clear is the role of these processes in driving changes in past atmospheric dust activity, and possible wider links between dust and climate. Terrestrial windblown dust (loess) deposits along the northern fringe of the European loess belt potentially record past atmospheric dust emission from regions close to the former Eurasian Ice Sheet (EIS) and provide a means to evaluate the role of ice sheet fluctuations in the past dust cycle. Numerical loess chronologies across this region generally agree on greatly enhanced dust deposition rates during MIS 2, when the EIS reached its maximum extent. Yet, uncertainties over the sources of this material prevent understanding of the precise causes of this greatly enhanced atmospheric dustiness, and any potential link to ice sheet fluctuations and climate. In southeast England, loess accumulation dominantly occurred in two phases centered on 25–23.5 ka and 20–19 ka, matching the timing of coalescence of the Fennoscandian and British-Irish ice sheets and specifically advances and retreats of nearby ice lobes in the western North Sea. As such, these deposits provide an ideal test of the role of ice sheet fluctuations in atmospheric dust dynamics. Here we undertake such a test through a detailed provenance study of loess in southeast England and potential dust source sediments across the North Sea region. We group extensive new and published data sets of detrital zircon U–Pb ages from basement rocks and Cenozoic sediments in the North Sea area, which not only provide new insight into both loess source, but also the nature of sediment transport over NW Europe into the North Sea basin more widely. Multi-proxy evidence allows us to unambiguously identify ice sheet derived sediments in the exposed North Sea basin as the dominant source of loess in southeast England, while fluvial sediments delivered by rivers draining Continental Europe possibly contributed additional source material to the first loess accumulation phase. We propose that sudden retreats of the North Sea Lobe released substantial amounts of sediment rich meltwater into the southern North Sea and Channel basins, driving accelerated dust emission, loess deposition and provenance variability in NW Europe during MIS 2. Moreover, we propose that this model of dust activity driven by proglacial sediment availability may be applicable for EIS marginal regions more widely, even where resultant loess cover is rarely preserved due to extensive erosion and reworking along the ice marginal spillway. This implies the role of ice sheets in controlling wider dust emission may be underestimated. In addition to driving changes in ocean circulation through meltwater pulses, ice sheet dynamics in the Quaternary may have also driven substantial and abrupt changes in atmospheric dust activity. This mechanism may in part explain the coupling between dust and climate events widely seen in Quaternary dust sediment records and suggests a possible major role of high latitude dust emission in MIS 2 dustiness across Europe and beyond.

Ostatni epizod vistuliańskiego chłodu: cechy diagnostyczne w obszarach ekstraglacjalnych

The general trend of paleogeographic events is dependent on global climate changes. In the analysis of short geological periods, a large role should be assigned to local conditions, understood both in the regional sense and, above all, at the microscale, i.e. the specificity of sites with different morphological location and lithological properties of the substratum, generating a strictly local course of morphogenetic processes reflected in geological records. In this context, a large role should be assigned to the smallest marks of disturbances. Interpretation difficulties that researchers of the Younger Dryas often encounter result from the small thickness of the sub-surface sediment and its weathering changes. The article shows how a detailed analysis of data from the abiotic sphere can be used to reconstruct the conditions prevailing in short geological periods. The area of study is situated in central Poland in an extraglacial zone of the last Quaternary ice sheet that during the Vistulian remained under periglacial conditions (Fig. 1). Among the diagnostic properties are: sedimentological palaeohydrological marks, traces of permafrost re-aggradation, oversnow deposits, aeolian specificity and random events. Changes in the hydrological regimes in rivers are reflected in changes in the sedimentary record showing effective floods (Fig. 2) and together with raising of groundwater table registered in biogenic baśni point two distinct phases of humidity. Traces of permafrost re-aggradation are scarce and found only in particular localities (e.g., under peatlands), but the environmental context of involutions reported from study sites allow us to conclude a return of frozen substratum (Figs 2, 4). The smallscale fissure and fault network in the deposits of the youngest unit of dry periglacial valleys dated to the Younger Dryas were linked to deposition on patches of frozen snow that lasted for several summers and, afterwards, a collapse of he deposit due to melting (Fig. 5). This process did not require the presence of permafrost. In the aeolian environment, the cool conditions of the Younger Dryas resulted locally in the deposition of thin sand covers (Figs 6, 8), which, in favourable topographic conditions, could even form initial dune ramparts (Fig. 7). In the Younger Dryas environment, morphogenetic processes may have been activated by a random event not necessarily associated with global climatic change. One potential example is traces of wildfires registered in a depositional sequence of the Żabieniec site.

Reactivation of Non‐Optimally Orientated Faults Due to Glacially Induced Stresses

AbstractThe deformation due to an ice load is accompanied by displacement and stress changes. These stress changes are known to have created large‐magnitude earthquakes along pre‐existing faults during and after deglaciation of the Late Quaternary ice sheets. However, these so‐called glacially induced faults have been found to be not optimally orientated in their respective regional stress regime. Here, we analyzed the potential of non‐optimally orientated fault reactivation within a glacially induced stress field as well as changes of the stress regimes due to these additional stresses. A finite element model is used to estimate glacially induced stresses, which are then combined with background stress magnitudes. Non‐optimally orientated faults can be reactivated by glacially induced stresses within thrust‐, strike‐slip‐, and normal‐faulting stress regimes, but depending on their location with respect to the ice sheet and their orientation within the regional stress field. While faults with large variations of dip and strike outside of the ice sheet are prone to reactivation when the background stress field is a normal‐ or strike‐slip‐faulting stress regime, faults within a thrust‐faulting stress regime can also be reactivated within the ice margin during and after the deglaciation. Outside the ice margin, instabilities in a thrust‐faulting stress regime develop along the intermediate principal stress axis. Stress regime changes can occur for all background stress states. Finally, we find that certain conditions in a strike‐slip‐faulting stress regime can also explain the observed glacially induced thrust faults in Northern Europe.

Quaternary ice sheets and sea level regression drove divergence in a marine gastropod along Eastern and Western coasts of South America

The southern coastline of South America is a remarkable area to evaluate how Quaternary glacial processes impacted the demography of the near-shore marine biota. Here we present new phylogeographic analyses in the pulmonate Siphonaria lessonii across its distribution, from northern Chile in the Pacific to Uruguay in the Atlantic. Contrary to our expectations, populations from the southwestern Atlantic, an area that was less impacted by ice during glacial maxima, showed low genetic diversity and evidence of recent expansion, similar to the patterns recorded in this study across heavily ice-impacted areas in the Pacific Magellan margin. We propose that Atlantic and Pacific shallow marine hard-substrate benthic species were both affected during the Quaternary in South America, but by different processes. At higher latitudes of the southeast Pacific, ice-scouring drastically affected S. lessonii populations compared to non-glaciated areas along the Chile-Peru province where the species was resilient. In the southwest Atlantic, S. lessonii populations would have been dramatically impacted by the reduction of near-shore rocky habitat availability as a consequence of glacio-eustatic movements. The increase of gravelly and rocky shore substrates in the southwest Atlantic supports a hypothesis of glacial refugia from where the species recolonized lower latitudes across the Atlantic and Pacific margins. Our results suggest that current patterns of genetic diversity and structure in near-shore marine benthic species do not solely depend on the impact of Quaternary glacial ice expansions but also on the availability of suitable habitats and life-history traits, including developmental mode, bathymetry and the likelihood of dispersal by rafting.

Microsedimentology of tills near Ainet, Austria - were palaeo-ice streams in the European Alps underlain by soft deforming bed zones?

Abstract Fast moving palaeo-ice masses within the European Alpine Ice Cap (EAIC) during the Last Glacial Maximum within the large valleys of the European Alps are likely comparable in terms of their subglacial conditions to ice streams that drained the larger Quaternary Ice Sheets in Europe and North America. Unlike these continental-style ice sheets, the ice inundating the European Alps, like the Cordilleran Ice Sheet in North America, flowed through confined bedrock valleys that, at close to the glacial maximum, acted in a similar manner to ice streams. Little mention exists as to the extent of soft sediment basal deformation in these deep valleys although increasingly such conditions are known from several parts of the EAIC. The Drau (Drava) ice stream during the Alpine Last Glacial Maximum (= Würmian Pleniglacial, ~ 29 – ~20 ka) as well as small tributary glacier during the early Lateglacial phase of ice decay (~20 – 19 ka) appears as a temperate, fast-moving ice mass that would likely be underlain by soft deforming sediment. It is the underlying microsedimentology of parts of the Drau Valley catchment in the Lienz area of Austria that is the focus of this paper. The tills in the Isel Valley at Ainet reveal a detailed depiction of soft sediment deformation processes throughout the basal zones of this ice stream illustrative of temperate basal ice conditions and comparable to those tills of northern Austria under the Inn Ice Stream. The tills exhibit the characteristics of ongoing active soft-sediment deformation. The evidence from Ainet supports the contention that most likely subglacial processes beneath ice streams in the palaeo-EAIC were comparable to those today in Antarctica and in the Quaternary ice streams of the Cordilleran, Laurentide and North European Ice Sheets.

Controlling the external moment arm at the knee allows better recovery after multiple slipping perturbations during gait

Global reconstructions of the Earth's Quaternary ice sheet history such as ICE-6G assume that mantle rheology is linear and Earth properties are laterally homogeneous. However, these assumptions are unrealistic because high temperature/pressure creep experiments show that both linear and non-linear creep laws operate simultaneously in the mantle. Also surface geology and seismic tomography show that mantle properties vary laterally. This study uses the Coupled Laplace-Finite Element Method to find an ice model that is consistent with an Earth model with composite rheology where both linear and non-linear creep laws operate simultaneously in the mantle, and the effective viscosity is laterally heterogeneous.We use the ICE-6G ice model as initial load on a composite rheology Earth model and iteratively improve both the ice and Earth model parameters until they fit observations of Glacial Isostatic Adjustment or GIA (relative sea level and land uplift rate) well simultaneously. We thereby focus on North America and northern Europe. Our best combination model, called ICE-C(M_C), also fits gravity rate-of-change data in both areas. This finding removes the obstacle in using composite rheology in GIA studies since previous work found it impossible for composite rheology to fit both relative sea level and land uplift rate data simultaneously. It shows that composite rheology is clearly an alternative to linear rheology in future GIA studies.The ICE-C model is at the last glacial maximum (LGM) position from 26 ka BP (thousand years before present) to 19 ka BP, which implies that composite rheology also supports the timing of LGM proposed by Clark et al. (2009). The model is found to be significantly thicker in the center of rebound in Fennoscandia than ICE-6G from the LGM to about 8 ka BP, but significantly thinner around the Fennoscandian coastline from LGM to about 12 ka BP. These changes in the lower boundary conditions in northern Europe may affect the reconstruction of past climate there. Regional differences in ice thickness between ICE-C and ICE-6G are also found in Laurentia. During LGM there are negligible differences in total ice volume between ICE-C and ICE-6G, thus it remains questionable if a composite rheology may help in solving the missing ice problem. ICE-C is also consistent with meltwater pulses 1A and 1B. Mantle viscosities and creep parameters of Earth model M_C are consistent with previous findings from GIA modeling and microphysics experiments.

In search of an ice history that is consistent with composite rheology in Glacial Isostatic Adjustment modelling

Global reconstructions of the Earth's Quaternary ice sheet history such as ICE-6G assume that mantle rheology is linear and Earth properties are laterally homogeneous. However, these assumptions are unrealistic because high temperature/pressure creep experiments show that both linear and non-linear creep laws operate simultaneously in the mantle. Also surface geology and seismic tomography show that mantle properties vary laterally. This study uses the Coupled Laplace-Finite Element Method to find an ice model that is consistent with an Earth model with composite rheology where both linear and non-linear creep laws operate simultaneously in the mantle, and the effective viscosity is laterally heterogeneous.We use the ICE-6G ice model as initial load on a composite rheology Earth model and iteratively improve both the ice and Earth model parameters until they fit observations of Glacial Isostatic Adjustment or GIA (relative sea level and land uplift rate) well simultaneously. We thereby focus on North America and northern Europe. Our best combination model, called ICE-C(M_C), also fits gravity rate-of-change data in both areas. This finding removes the obstacle in using composite rheology in GIA studies since previous work found it impossible for composite rheology to fit both relative sea level and land uplift rate data simultaneously. It shows that composite rheology is clearly an alternative to linear rheology in future GIA studies.The ICE-C model is at the last glacial maximum (LGM) position from 26 ka BP (thousand years before present) to 19 kaBP, which implies that composite rheology also supports the timing of LGM proposed by Clark et al. (2009). The model is found to be significantly thicker in the center of rebound in Fennoscandia than ICE-6G from the LGM to about 8 kaBP, but significantly thinner around the Fennoscandian coastline from LGM to about 12 kaBP. These changes in the lower boundary conditions in northern Europe may affect the reconstruction of past climate there. Regional differences in ice thickness between ICE-C and ICE-6G are also found in Laurentia. During LGM there are negligible differences in total ice volume between ICE-C and ICE-6G, thus it remains questionable if a composite rheology may help in solving the missing ice problem. ICE-C is also consistent with meltwater pulses 1A and 1B. Mantle viscosities and creep parameters of Earth model M_C are consistent with previous findings from GIA modeling and microphysics experiments.

Paleoclimate's factors of reconstruction of thermal history of petroleum bazhenov and togur suites southeastern West Siberia

The regions of the West Siberian oil and gas province have unique paleoclimatic features: 1) Mesozoic-Cenozoic secular course of temperature, individual for regional paleoclimatic zones; 2) different scale processes of formation and degradation of Neopleistocene permafrost sections; 3) zonal and periodically forming late Quaternary ice sheets. The purpose of research is to assess the influence of factors paleoclimate (secular temperature course on the earth's surface and Neopleistocene permafrost strata) on the calculated geothermal regime of parent oil-source suites that determines the calculation of the density of hydrocarbon resources by three-dimensional-genetic method. The object of research are the Bazhenov and Togur deposits of Mesozoic and Cenozoic section, stripped by deep wells in the south-east of Western Siberia (North Festival and Luginetskoye hydrocarbon deposits of Tomsk region). Research is based on the method paleotemperature simulation — solving the inverse and direct problems of unsteady geothermy under conditions of sedimentation on multivariance of paleotectonic and paleotemperature reconstructions, on conformity assessment of results reconstructions to the criteria of optimal solution of the inverse problems of geophysics and the degree of harmonization of rated centers of generation of oils with established oil and gas presence in the interior. The necessity to take into account Neopleistocene permafrost of about 300 meters thick and of the use of local (regional) secular progress of temperatures on the earth's surface for adequately recover of thermal history of parent oil source deposits on the lands of southeast Western Siberia has been established. In case of permafrost strata are neglected estimated hydrocarbon resources HR, determined by the volume-genetic method, can be underestimated up to 25—30 %. In the case of neglecting paleoclimatic temperatures running calculated HR can be underestimated from 50 % to 4 times lower.

Past ice flow in Wahlenbergfjorden and its implications for late Quaternary ice sheet dynamics in northeastern Svalbard

Wahlenbergfjorden is a fjord situated in the western part of Nordaustlandet in northern Svalbard. It leads into the 400 m deep Hinlopen Strait located between Nordaustlandet and Spitsbergen. High-resolution multibeam bathymetric and sub-bottom data, as well as sediment cores are used to study the past extent and dynamics of glaciers in Wahlenbergfjorden and western Nordaustlandet. The submarine landform assemblage in Wahlenbergfjorden consists of landforms characteristic of subglacial, ice marginal and proglacial conditions. Glacial lineations indicate that Wahlenbergfjorden was occupied by streaming ice during the LGM and most likely acted as an ice stream onset zone. Westward ice flow in the fjord merged with the ice stream in Hinlopen Strait. Absence of ice recessional landforms in outer Wahlenbergfjorden suggests relatively fast deglaciation, possibly by flotation of the glacier front in the deeper parts of the fjord. The inner part of Wahlenbergfjorden and Palanderbukta are characterized by De Geer moraines, indicating episodic retreat of a grounded glacier front. In Palanderbukta, longer still stands of the glacier terminus resulted in the formation of larger terminal moraine ridges. The inner part of Wahlenbergfjorden was deglaciated prior to 11.3 ± 55 Cal. ka BP. The submarine landform assemblages in front of Bodleybreen, Etonbreen, Idunbreen, Frazerbreen and Aldousbreen confirm that these glaciers have surged at least once during the Holocene.

Glaciation of Siberia and the problem of massive ice beddings

As a result of many years of the author’s studies of glaciers and ground ices, a great amount of factual material has been collected for a purpose to analyze a possibility of burying the glaciers in the permafrost zone and to esti‑ mate a time of their stay in such а condition. According to the author’s opinion, the Siberian glaciers were mainly the valley ones; ice sheets were never formed, and any existence of buried glaciers could not be real in the geo‑ logical time scale. However, some researchers still believe that in the Quaternary ice sheets occurred in the North of Siberia, and, in addition, they consider the local massive ice beddings as relics of these sheets. No clear expla‑ nation of the similar origin of such ice structures exists at the present time, so development and variety of this ice could be easier explained by the permafrost genesis. Basing on results of observations carried out in all glacier regions of Siberia, the author concludes that glaciers cannot exist in the form of buried ice for a long time. This is unrealistic even in the North‑East of Siberia, where the absolute minimum temperature is −67.8 °C, and the mean annual air temperature drops below −17 °C. The characteristic feature of the Siberia continental climate is short, but hot summer. In such a situation, the coarse fragmental morainic material, covering glaciers by the layer up to 3 m thick, cannot preserve the underlying ice from melting because the heat penetrates down with the air, liquid precipitation, and the melt water. When glaciers reduce, the dead ice, buried under a moraine, may be preserved in the coldest areas of Siberia for only 100–150 years. Therefore, despite the resemblance of the scarps of the ice bodies having the permafrost or glacial origin, consideration of them as relics of ancient glaciers would be wrong.

Possible ‘lift-off moraines’ at grounded ice-sheet margins, North Norwegian shelf edge

Small but regular variations in ice-sheet horizontal velocity have been linked to buoyancy-related tidal forcing beneath modern Antarctic ice streams (e.g. Bindschadler et al. 2003; Gudmundsson 2006). Given this sensitivity to tidal amplitudes of only a metre or two, it is likely that grounding zones at the tidewater margins of Quaternary ice sheets were also affected by buoyancy changes linked to tides. Ottesen & Dowdeswell (2009) observed a linear belt of irregular hummocky seafloor terrain at the full-glacial margin of a grounded Late Quaternary ice sheet at the NW Spitsbergen shelf edge. They proposed that this distinctive morphology might be linked to buoyancy fluctuations at this former grounding zone. We describe and interpret extensive belts of similar hummocky terrain from the margins of a full-glacial ice sheet at the North Norwegian shelf edge. Between 68° 50′ N and 69° 25′ N, the Norwegian continental shelf narrows to about 30 km off Vesteralen archipelago. This area comprises shallow banks (40–120 m deep) and is understood to have been located between fast-flowing ice streams in the Late Weichselian Ice Sheet; it is therefore likely to have experienced limited ice flow. Within 6 km of the shelf edge, belts of hummocky, undulating ridges are found both on banks (Fig. 1) and in shallower parts of adjacent troughs. The ridges occur at water-depths of 85–160 m, and …

Skjoldryggen terminal moraine on the mid-Norwegian shelf

Terminal moraines are relatively large ridges of diamictic glacial debris produced at the outermost margins of past glaciers and ice sheets. Their identification on land is important in mapping the maximum extent of Quaternary ice sheets (e.g. Svendsen et al. 2004; Benn & Evans 2010). In marine environments where fast-flowing ice streams reach the shelf edge during full-glacial intervals, moraine ridges are not usually present and the seafloor is characterized by parallel-to-flow streamlined sediments (Ottesen & Dowdeswell 2009). Submarine terminal moraine ridges, by contrast, appear more typical of slower-flowing marine ice margins (Dahlgren et al. 2002; Dowdeswell & Elverhoi 2002; Dowdeswell et al. 2016). A very large ridge, about 150 km long and up to approximately 200 m high relative to the adjacent shelf, is located on the outermost part of the mid-Norwegian continental shelf edge between about 65° and 66° N (Fig. 1a). It is known as Skjoldryggen (‘skjold’ means ‘shield’ and ‘ryggen’ means ‘the ridge’ in Norwegian). Along most of its length, the ridge has a steeper offshore slope relative to …

The Sleipner storage site: Capillary flow modeling of a layered CO2 plume requires fractured shale barriers within the Utsira Formation

To prevent ocean acidification and mitigate greenhouse gas emissions, it is necessary to capture and store carbon dioxide. The Sleipner storage site, offshore Norway, is the world's first and largest engineered waste repository for a greenhouse gas. CO2 is separated from the Sleipner gas condensate field and stored in the pore space of the Utsira Formation, a saline aquifer approximately 1km below the surface and 200km from the coast. Statoil, the field operator, has injected almost 1Mt/yr of captured CO2 into the storage site since 1996. The buoyant CO2 plume ascended rapidly through eight thin shale barriers within the aquifer to reach the top seal in less than three years. The plume's progress has been monitored by eight seismic surveys, as well as gravimetric and electromagnetic monitoring, which record the spreading of nine thin CO2 layers. This paper presents a capillary flow model using invasion percolation physics that accurately matches the plume's geometry. The approach differs from standard Darcy flow simulations, which fail to match the plume geometry. The calibrated capillary flow simulation indicates that a mass balance for the plume is likely, but can only replicate the plume geometry if the thin intra-formational shale barriers are fractured. The model enables an estimate of the shale barrier behavior and caprock performance. The fractures are very unlikely to have been caused by CO2 injection given the confining stress of the rock and weak overpressure of the plume, and so fracturing must pre-date injection. A novel mechanism is suggested: the deglaciation of regional ice sheets that have rapidly and repeatedly unloaded approximately 1km of ice. The induced transient pore pressures are sufficient to hydro-fracture thin shales. The fractures enable fast CO2 ascent, resulting in a multi-layered plume. Shallow CO2 storage sites in the Northern North Sea and other regions that have been loaded by Quaternary ice sheets are likely to behave in a similar manner.

The Fate of Greenland— Lessons from Abrupt Climate Change

In times of chronic lack of resources for academic research and ever increasing competition for grants it was every scientists dream coming true: a billionaire patron comes along and hands you unlimited resources to pursue the research that lies closest to your heart. In this case, the late Gary Comer (1927–2006), who had in 2001 taken his yacht through the notorious Northwest Passage then free of sea ice, engaged a team of outstanding climate scientists to lead a search for causal links controlling abrupt global climate change: Wallace (Wally) S. Broecker of Columbia University, George H. Denton of the University of Maine, and Richard B. Allen of Pennsylvania State University. Broecker is an oceanographer/geochemist, who is probably best known for developing the idea of a global “conveyor belt” linking the circulation of the global oceans and controlling large scale climate oscillations in the past; Denton is a geologist, long concerned with the (bi-polar) geological history of the large Quaternary ice sheets; and Alley is a glaciologist who is perhaps best known for his contributions on the relationships between Earth's cryosphere and global climate change. All three have developed ideas and concepts on rapid ocean-atmosphere-cryosphere reorganizations over past glacial cycles. Philip Conkling, a prominent Maine naturalist who participated in many of Comer’s expeditions, played a vital role in putting the team together.

The spatial variation of weathering and soil depth across a Triassic sandstone outcrop

AbstractIn this study, we used an archive of borehole logs from the British Geological Survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the Triassic Sherwood Sandstone Group outcrop (750 km2), in the East Midlands, UK. The borehole logs were used to estimate the thickness of the soil (n = 280) and soil and saprolite (S&S) to competent rock (n = 500). The weathering profile of the sandstone consisted of soil (median thickness ∼ 1·5 m) overlying a transition zone of compacted and weakly cemented weathered sandstone saprolite over bedrock. Topographic analysis using a NEXTMAP 5 m × 5 m digital elevation model (DEM) revealed no significant relationships between slope properties (relief, flow length, flow accumulation or slope angle) and soil or S&S thickness. A weak, but statistically significant correlation was found between the thickness of the soil and S&S (rs = 0·25, p < 0·001, n = 192). The variation in soil thickness may be related to changes in current and historic and land‐use, variation in sandstone properties and the influence of glacial/peri‐glacial processes. The thickness of the saprolite was more variable towards the southern part of the study area, where it increased to a maximum 40 m. We hypothesize and provide evidence that the greater weathering thickness is related to the occurrence of increased faulting in this part of the study region, allowing increased access to meteoric waters. A possible source of increased water supply is meltwater from Quaternary ice sheets; the overburden of ice may have increased sub‐glacial pore water pressure, with the fractures and faults acting as a drainage system for the removal of dissolved weathering products. British Geological Survey © NERC 2010

Late Quaternary ice sheet extents in northeastern Germany inferred from surface exposure dating

We determined in situ cosmogenic 10Be ages for 11 boulders on the Hoher Fläming ice marginal belt and five boulders on the Gerswalder moraine, a recessional moraine of the Pomeranian stage. Previous time estimations for the deposition of these moraines along the southern margin of the Scandinavian Ice Sheet (SIS) in northeastern Germany are mostly based on geomorphology and stratigraphy, and on few radiocarbon dates and recently published surface exposure ages in the case of the Pomeranian moraine. Our new exposure ages range from 21.7±1.2 10Beka to 172.6±6.0 10Beka for the Hoher Fläming ice marginal belt. The wide range of exposure ages may reflect episodic ice marginal belt modification due to intensified erosion by meltwater channeled in the Baruther Urstromtal, (ice marginal valley) accompanied by long-lasting erosional processes like solifluction and aeolian deflation.For the Gerswalder moraine, our new exposure ages range from 12.3±0.6 10Beka to 16.6±1.0 10Beka. Excluding the youngest sample (BER-97-03), we calculated error-weighted mean ages ranging from 15.2±0.5 10Beka to 16.0±0.5 10Beka (n=4), depending on choice of scaling methods, surface erosion and snow cover. These results firmly establish the position of the southern margin of the SIS in northeastern Germany during the Gerswalder substage a recessional phase of the Pomeranian stage.

Late Quaternary ice sheet, lake and sea history of southwest Scandinavia – a synthesis

Based on a large number of new boreholes in northern Denmark, and on the existing data, a revised event‐stratigraphy is presented for southwestern Scandinavia. Five significant Late Saalian to Late Weichselian glacial events, each separated by periods of interglacial or interstadial marine or glaciolacustrine conditions, are identified in northern Denmark. The first glacial event is attributed to the Late Saalianc. 160–140 kyr BP, when the Warthe Ice Sheet advanced from easterly and southeasterly directions through the Baltic depression into Germany and Denmark. This Baltic ice extended as far as northern Denmark, where it probably merged with the Norwegian Channel Ice Stream (NCIS) and contributed to a large discharge of icebergs into the Norwegian Sea. Following the break up, marine conditions were established that persisted from the Late Saalian until the end of the Early Weichselian. The next glaciation occurredc. 65–60 kyr BP, when the Sundsøre ice advanced from the north into Denmark and the North Sea, where the Scandinavian and British Ice Sheets merged. During the subsequent deglaciation, large ice‐dammed lakes formed before the ice disintegrated in the Norwegian Channel, and marine conditions were re‐established. The following Ristinge advance from the Baltic, initiatedc. 55 kyr BP, also reached northern Denmark, where it probably merged with the NCIS. The deglaciation,c. 50 kyr BP, was followed by a long period of marine arctic conditions. Around 30 kyr BP, the Scandinavian Ice Sheet expanded from the north into the Norwegian Channel, where it dammed the Kattegat ice lake. Shortly after,c. 29 kyr BP, the Kattegat advance began, and once again the Scandinavian and British Ice Sheets merged in the North Sea. The subsequent retreat to the Norwegian Channel led to the formation of Ribjerg ice lake, which persisted from 27 to 23 kyr BP. The expansion of the last ice sheet startedc. 23 kyr BP, when the main advance occurred from north–northeasterly directions into Denmark. An ice‐dammed lake was formed during deglaciation, while the NCIS was still active. During a re‐advance and subsequent retreatc. 19 kyr BP, a number of tunnel‐valley systems were formed in association with ice‐marginal positions. The NCIS finally began to break up in the Norwegian Sea 18.8 kyr BP, and the YoungerYoldiaSea inundated northern Denmark around 18 kyr BP. The extensive amount of new and existing data applied to this synthesis has provided a better understanding of the timing and dynamics of the Scandinavian Ice Sheet (SIS) during the lastc. 160 kyr. Furthermore, our model contributes to the understanding of the timing of the occasional release of large quantities of meltwater from the southwestern part of the SIS that are likely to enter the North Atlantic and possibly affect the thermohaline circulation.

The impact of Quaternary glaciations on inselbergs in northern Sweden

We investigate the glacial modification of inselbergs (large, isolated bedrock hills) in northern Sweden. Inselbergs are generally regarded as products of deep weathering (etching) and stripping under warm and humid climates. Unlike inselbergs found in the tropics, the inselbergs in northern Sweden were exposed to ice sheet glaciation for long periods of the Quaternary. We used DEMs to examine 794 inselbergs in our study area and they were classified according to their degree of glacial modification. Bedrock structural control was assessed using GIS data on the regional geology. Clusters of inselbergs were mapped in the field for features indicative of glacial erosion, such as glacial cliffs and stripped bedrock surfaces, and for features indicative of limited erosion, such as tors and blockfields. The results of the study indicate that inselbergs in the area were mostly modified by Quaternary ice sheets only to a low or moderate extent and that the degree of glacial erosion is dependent on their relief and location. Inselbergs with a relative relief of < 100 m and in areas of lower absolute relief experienced the strongest glacial modification, where the strongest glacial modification can result in lateral erosion of the inselberg flanks. Inselberg summits often display signs of minimal glacial erosion, such as torlike bedrock outcrops with signs of strong weathering. In summary, we argue that inselbergs in northern Sweden have largely retained their pre-Quaternary shape despite long periods of ice sheet cover.