Local and regional constraints on relative sea-level changes in southern Isle of Skye,Scotland, since the Last Glacial Maximum

New relative sea-level (RSL) data constrain the timing and magnitude of RSL changes in the southern Isle of Skye following the Last Glacial Maximum (LGM). We identify a marine limit at ~23 m OD, indicating RSL ~20 m above present c. 15.1 ka. Isolation basin data, supported by terrestrial and marine limiting dates, record an RSL fall to 11.59 m above present by c. 14.2 ka. This RSL fall occurs across the time of global Meltwater Pulse 1A, supporting recent research on the sources of ice melting. Our new data also help to resolve some of the chronological issues within the existing Isle of Skye RSL record and provide details of the sub-Arctic marine environment associated with the transition into Devensian Lateglacial climate at c. 14.5 k cal a bp , and the timing of changes in response to the Loch Lomond Stadial climate. Glacio-isostatic adjustment (GIA) model predictions of RSL deviate from the RSL constraints and reflect uncertainties in local and global ice models used within the GIA models. An empirical RSL curve provides a target for future research.     

Late Devensian and Holocene relative sea‐level changes on the Isle of Skye,Scotland, UK

Detailed litho‐ and biostratigraphical analyses from three coastal sites in contrasting coastal settings on the Isle of Skye, Scotland, UK, reveal evidence for several changes in relative sea level during the Late Devensian and Holocene. At the start of the record, relative sea level in the area was high at ca. 12 500 ¹⁴C (ca. 14 800 cal.) yr BP but then fell, reaching a low point during the Younger Dryas, at ca. 11 000–10 000 ¹⁴C (ca. 13 000–11 600 cal.) yr BP, when a rock platform, correlated with the Main Rock Platform, was formed. In the early–middle Holocene, relative sea level was rising by ca. 8000 ¹⁴C (ca. 8800 cal.) yr BP and in northeast Skye a lagoonal surface, correlated with the Main Postglacial Shoreline, was formed at ca. 6600 ¹⁴C (ca. 7500 cal.) yr BP. By the late Holocene, relative sea level was again falling, but a rise, registered at at least two sites, began probably before ca. 4000 ¹⁴C (ca. 4500 cal.) yr BP, and a second lagoonal surface in northeast Skye, correlated with the Blairdrummond Shoreline, was formed, although by ca. 3000 ¹⁴C (ca. 3200 cal.) yr BP relative sea level in the area had resumed its downward trend. The pattern of relative sea‐level changes disclosed is compared with evidence elsewhere in Scotland. Copyright © 2006 John Wiley & Sons, Ltd.     

Geomorphological signature and flow dynamics of The Minch palaeo‐ice stream,northwest Scotland

Large‐scale streamlined glacial landforms are identified in 11 areas of northwest Scotland, from the Isle of Skye in the south to the Butt of Lewis in the north. These ice‐directional features occur in bedrock and superficial deposits, generally below 350 m above sea level, and where best developed have elongation ratios of >20:1. Sidescan sonar and multibeam echo‐sounding data from The Minch show elongate streamlined ridges and grooves on the seabed, with elongation ratios of up to 70:1. These bedforms are interpreted as mega‐scale glacial lineations. All the features identified formed beneath The Minch palaeo‐ice stream which was ca. 200 km long, up to 50 km wide and drained ca. 15 000 km² of the northwest sector of the last British‐Irish Ice Sheet (Late Devensian Glaciation). Nine ice‐stream tributaries and palaeo‐onset zones are also identified, on the basis of geomorphological evidence. The spatial distribution and pattern of streamlined bedforms around The Minch has enabled the catchment, flow paths and basal shear stresses of the palaeo‐ice stream and its tributaries to be tentatively reconstructed. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

Cosmogenic 10Be insights into the extent and chronology of the last deglaciation in Wester Ross,northwest Scotland

Cosmogenic ¹⁰Be surface exposure ages for bedrock sites around Torridon and the Applecross Peninsula in Wester Ross, northwest Scotland, provide new insights into the Lateglacial transition. Accounting for postglacial weathering, six statistically comparable exposure ages give a late Younger Dryas (G‐1) exposure age of 11.8 ± 1.1 ka. Two further outliers are tentative pre‐Younger Dryas exposure ages of 13.4 ± 0.5 ka in Torridon, and 17.5 ± 1.2 ka in Applecross. The Younger Dryas exposure ages have compelling implications for the deglaciation of marginal Loch Lomond Stadial ice fields in Torridon and Applecross. Firstly, they conflict with predictions of restricted ice cover and rapid retreat based on modelling experiments and climate proxies, instead fitting a model of vertically extensive and prolonged ice coverage in Wester Ross. Secondly, they indicate that >2 m of erosion took place in the upper valleys of Torridon and Applecross during the Younger Dryas, implying a dominantly warm‐based glacial regime. Finally, the exposure ages have clarified that corrie (cirque) glaciers did not readvance in Wester Ross, following final deglaciation. Copyright © 2011 John Wiley & Sons, Ltd.     

In situ cosmogenic exposure ages from the Isle of Skye,northwest Scotland: implications for the timing of deglaciation and readvance from 15 to 11 ka

We present 10 in situ cosmogenic exposure ages from two moraines on the Isle of Skye. The Strollamus medial moraine was deposited during deglaciation of the Devensian ice sheet and yields a mean exposure age from five samples of 14.3 ± 0.9 ka. The moraine age indicates that a significant ice mass existed on Skye at the time of a regional readvance recorded in Wester Ross, northwest Scotland. Taken at face value the ages suggest that deglaciation did not occur until well into Greenland Interstade 1. The Slapin moraine represents the local limit of the Loch Lomond Readvance (LLR) and yields a mean exposure age from five samples of 11.5 ± 0.7 ka, which is consistent with deposition relating to the LLR. These ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end. This scenario is considered unlikely given the nature of the climate during this period, which leads us to call for a locally calibrated production rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Periglacial trimlines,former nunataks and the altitude of the last ice sheet in Wester Ross,northwest Scotland

High-level weathering limits separating ice-scoured topography from frost-weathered detritus were identified on 28 mountains in Wester Ross at altitudes of 700–960 m, and a further 22 peaks support evidence of ice scouring to summit level. Weathering limits are defined most clearly on sandstone and gneiss, which have resisted frost shattering during the Late Devensian Lateglacial, but can also be distinguished on schists and quartzite. Schmidt hammer measurements and analyses of clay mineral assemblages indicate significantly more advanced rock and soil weathering above the weathering limits. The persistence of gibbsite above weathering limits indicates that they represent the upper limit of Late Devensian glacial erosion. The regular decline of weathering-limit altitudes along former flowlines eliminates the possibility that the weathering limits represent former thermal boundaries between protective cold-based and erosive warm-based ice. The weathering limits are therefore interpreted as periglacial trimlines that define the maximum surface altitude of the last ice sheet. Calculated basal shear stresses of 50–95 kPa are consistent with this interpretation. Reconstruction of ice-sheet configuration indicates that the former ice-shed lay above 900 m along the present watershed, and that the ice surface descended northwestwards, with broad depressions along major troughs and localised domes around independent centres of ice dispersal. Extrapolation of the ice surface gradient and altitude suggests that the ice sheet did not overrun the Outer Hebrides, but was confluent with the independent Outer Hebrides ice-cap in the North Minch basin. Erratics located up to 140 m above the reconstructed ice surface are inferred to have been emplaced by a pre-Late Devensian ice sheet (or ice sheets) of unknown age. © 1997 John Wiley & Sons, Ltd.     

High-resolution reconstruction of the last ice sheet in NW Scotland

Reconstructions of the last (late Devensian) British ice sheet have hitherto been based on assumptions regarding its extent and form. Here we employ observational evidence for the maximum altitude of glacial erosion (trimlines) on mountains that protruded through the ice (palaeonunataks) to reconstruct the form of the ice sheet over ≈ 10 000 km² of NW Scotland. Contrasts in the clay mineralogy of soils and exposure ages of rock surfaces above and below these trimlines confirm that they represent the upper limit of late Devensian glacial erosion. The reconstruction yields realistic values of basal shear stress and is consistent with independent evidence of ice movement directions. The ice sheet reached ≈ 950 m altitude over the present N–S watershed, descended northwards and north-westwards, was deflected around an ice dome on Skye and an independent Outer Hebrides ice cap, and probably extended across the adjacent shelf on a bed of deforming sediments.     

Did large ice caps persist on low ground in north‐west Scotland during the Lateglacial Interstade?

Recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north‐west Scotland throughout the Lateglacial Interstade (≈ Greenland Interstade 1, ca. 14.7–12.9 ka), and that glacier ice was much more extensive in this area during the Older Dryas chronozone (ca. 14.0 ka) than during the Younger Dryas Stade (ca. 12.9–11.7 ka). We have recalibrated the same exposure age data using locally derived ¹⁰Be production rates. This increases the original mean ages by 6.5–12%, implying moraine deposition between ca. 14.3 and ca. 15.1 ka, and we infer a most probable age of ca. 14.7 ka based on palaeoclimatic considerations. The internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin (the Wester Ross Readvance). Pollen–stratigraphic evidence from a Lateglacial site at Loch Droma on the present drainage divide demonstrates deglaciation before ca. 14.0 ka, and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade (ca. 14.7–14.0 ka). This inference appears consistent with Lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer. Our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in Scotland between 14 and 13 ka, that large active glaciers probably survived throughout the Lateglacial Interstade and that ice extent was greater during the Older Dryas period than during the Younger Dryas Stade. Copyright © 2011 John Wiley & Sons, Ltd.     

Glacial meltwater erosion of the Mid-Cheshire Ridge: implications for ice dynamics during the Late Devensian glaciation of northwest England

Mapping of glacial meltwater channels along the length of the 25-km Mid-Cheshire Ridge reveals evidence for four distinctive channel morphologies, which are used to establish the pattern of meltwater flow during the Late Devensian glaciation. A key characteristic of all channels is an abrupt change in morphology between inception on the Mid-Cheshire Ridge and the downstream continuation on the surrounding Cheshire Plain, with large reductions in channel cross-sectional area at this point. The interpretation of this evidence is that meltwater flowing off the bedrock ridge was absorbed into a layer of permeable sediment beneath the Late Devensian ice sheet. This permeable sediment is significant because it would have acted as a deforming layer beneath the former ice sheet in this area. Reconstruction of the Late Devensian ice sheet based on information from the meltwater channels and using values of shear stresses typical of ice sheets resting on deformable beds (ca. 20 kPa) suggests an ice surface elevation over the Irish Sea of ca. 700 m. This value is considerably less than previous estimates of the vertical extent of the ice sheet of ca. 1000–1200 m and has important implications for the rapidity and mode of deglaciation during the Late Devensian. Copyright © 1999 John Wiley & Sons, Ltd.     

Dimensions and deglacial chronology of the Outer Hebrides Ice Cap,northwest Scotland: implications of cosmic ray exposure dating

Cosmic ray exposure ages of frost-weathered bedrock from mountain summits in the Outer Hebrides exceed the age of Late Devensian glaciation. Exposure ages of most glacially-abraded bedrock surfaces at low and intermediate elevations are younger than the age of maximum Late Devensian glaciation. These results confirm that previously mapped periglacial trimlines in the Outer Hebrides define the upper limit of bedrock erosion by Late Devensian ice. They are consistent with the interpretation, based on geomorphological evidence, that the trimlines mark the approximate upper limit of a Late Devensian Outer Hebrides Ice Cap. A postglacial exposure age from the summit of Oreval (662 m) suggests that this mountain was overrun during the last glaciation, indicating thicker ice cover and a lower surface gradient west of the ice-cap divide than previously inferred. Although bedrock surfaces below the trimlines are strongly ice-moulded, some show evidence of prior cosmic ray exposure, which we attribute to limited erosion during Late Devensian glaciation. If this interpretation is correct, the youngest apparent ages from these surfaces give the most reliable dates for deglaciation, at ca. 14.5–14 ka. This implies that ice persisted at favourable sites through the warm opening phase of the Windermere Interstade. Comparison with radiocarbon-dated evidence from offshore cores suggests net ice margin retreat of ∼74 km eastwards across the adjacent shelf in > 2.3 ± 1.0 ka. The dating evidence is consistent with relatively rapid retreat of calving margins to the coast, then slower withdrawal of ice margins to high ground. Copyright © 2005 John Wiley & Sons, Ltd.     

The Loch Lomond Readvance on the Isle of Skye,Scotland: Glacier reconstruction and palaeoclimatic implications

Geomorphological mapping of southern Skye indicates evidence for a single readvance of locally-nourished glaciers. These comprised a major icefield that occupied c. 155 km² of the main mountain area, a small icefield c. 10 km² in extent in the Kyleakin hills and ten corrie glaciers with a total area of c. 16 km². The absence of Lateglacial pollen sites, shorelines and periglacial features within the limits of local glaciation implies a Loch Lomond Readvance age for this glacial event. The area-weighted mean equilibrium line altitude (ELA) of the reconstructed Loch Lomond Readvance glaciers (319 m) conforms with a regional eastwards rise in ELAs that indicates dominant westerly airstreams during the Loch Lomond Stadial. An easterly decline in ELAs across the former icefields is interpreted in terms of easterly transfer of snow across ice-sheds by westerly winds, though the altitudes of corrie glacier ELAs suggest that the dominant snow-bearing winds were southerlies. Calculations based on the area-weighted mean ELA for the major icefield (308 m) indicate a stadial mean July sea-level temperature of c. 6 °C. The anomalously low gradients of certain former icefield outlet glaciers are attributed to deformation of subglacial sediment, an effect that may vitiate the assumption of linear ablation/accumulation gradients in the calculation of former ELAs for reconstructed glaciers.     

Late Devensian environments in the Vale of Mowbray, North Yorkshire, UK: evidence from palynology

Two radiocarbon-dated Lateglacial pollen diagrams from the Vale of Mowbray (northern Vale of York) are presented from sites in the lowlands between the washlands courses of the rivers Swale and Ure in North Yorkshire, an area with little previous palynological research despite its proximity to the Devensian glacial advance limits in eastern England. The profiles, from Snape Mires and Nosterfield, include the Loch Lomond Stadial (Younger Dryas) and the Holocene transition, while that from Snape Mires also includes the period from the early part of the Lateglacial Interstadial. This profile differs from most published Interstadial diagrams from the Yorkshire region in having a long-delayed expansion of tree and shrub taxa. Juniperus (juniper) remains important after vegetation development takes place and the pollen record includes evidence of two cold climate oscillations before the maximum development of Betula (birch) woodland near the end of the Lateglacial Interstadial. At both profiles Artemisia (mugwort) frequencies are lower during the Loch Lomond Stadial than at many regional sites, probably due to edaphic factors in these lowland locations. The two sites provide valuable environmental data that enable comparison between the more wooded Lateglacial vegetation to the south in the Vale of York and Humberside and the more open contemporaneous vegetation to the north in the Durham and Northumberland lowlands.     

Identification and significance of a visible,basalt‐rich Vedde Ash layer in a Late‐glacial sequence on the Isle of Skye,Inner Hebrides,Scotland

This paper reports the discovery of a visible, tephra horizon of Late‐glacial age from the site of Loch Ashik in the Isle of Skye, the Inner Hebrides, Scotland. Although the tephra shards have a bimodal geochemical composition identical to that of the Vedde Ash (a well known marker horizon within Late‐glacial sequences. The horizon at Ashik is dominated by basaltic shards and devitrified tephra shards, giving the layer its characteristic black colour. Only rhyolitic shards have previously been reported from Vedde Ash horizons in the British Isles. This new evidence raises some important questions about the factors that govern the distribution and accumulation of basaltic tephra, and about the methods used to detect ash shards in basins distal to centres of volcanic activity. Copyright © 2001 John Wiley & Sons, Ltd.     

The vertical extent of ice sheets in Nordfjord, western Norway: measuring degree of rock surface weathering

Degree of rock surface weathering was measured on sites in Oldedalen and Brigsdalen, where dates of deglaciation have been estimated. and on an altitudinal transect on the slopes of Skåla. representing one of the highest supra-marine reliefs in western Norway. The Schmidt hammer is useful only for distinguishing sites deglaciated during the Little Ice Age from those deglaciated during the Lateglacial and early Holocene. Degree of roughness of granitic augen gneiss bedrock surfaces was quantified from profiles measured in situ using a micro-roughness-meter and profile gauge. There is a significant increase in surface roughness above a clear trimline at c. 1350 m a.s.I. but no significant increase above a higher trimline previously proposed as the vertical limit of the last ice sheet in this area (c. 1560 m a.s.I.). The roughness of boulder surfaces on the summit blockfield does not direr significantly from the roughness of bedrock surfaces downslope as far as the lower trimline. These unexpected results suggest that bedrock surfaces between the two trimlines were not glacially abraded during the Late Weichselian, so that the upper trimline is unlikely to represent the vertical limit of ice during either the Late Weichselian or a subsequent readvance. Preliminary results of ¹⁰Be dating of surface quartz samples from above the lower trimline support the proposal that the site was not abraded during the last glaciation. The results can be interpreted in two ways: (1) The upper trimline represents the vertical limit of a pre-Late Weichselian advance. During the Late Weichselian the mountains were completely covered but surfaces down to the lower trimline were protected by cold-based ice. (2) The lower trimline marks the vertical limit of the Late Weichselian ice and the upper limit an older and more extensive glaciation.     

Drumlin formation in Southern Anglesey and Arvon,Northwest Wales

This is a study of Late Devensian drumlins formed in southern Anglesey and Arvon, northwest Wales. This area was affected by ice sheet coalescence when the Welsh ice sheet met with the lrish Sea ice sheet, and drumlins were formed once the two had coalesced. It is suggested that the drumlins were the result of net subglacial soft-bed erosion, and that they represent more resistant cores within the subglacial deforming layer. The drumlins have either gravel or till cores, and where the core was deformable, large-scale compressive glaciotectonic structures were seen (e.g. Dinas Dinlle) with local subglacial compression of –59%. Where the cores were more resistant (e.g. Lleiniog) these were not deformed but remained as more competent masses within the deforming layer. It is suggested that the less competent material flowed around the cores, some remaining as a thin carapace, but most of the material being removed down glacier, leaving the drumlins as erosional remnants. In northwest Wales there is a multi-till sequence that traditionally has been interpreted as having been deposited as the result of separate ice-sheet advances and retreats. However, in this study, it is suggested that the different tills were deposited as the result of ice-sheet coalescence, and that sites such as Dinas Dinlle do not show evidence of a major readvance in the retreat of the Devensian ice, but are indicative of continuously changing conditions within the subglacial deforming bed.     

A revised seismic stratigraphy for Quaternary deposits on the inner continental shelf west of Scotland between 55°30'N and 57°30'N

A stratigraphy for Quaternary deposits on the western Scottish shelf has been erected using seismic and borehole data. Eight new formations are defined and described with evidence presented for the environ-ment of deposition of each formation. Most of the Quaternary sediments preserved on the shelf arc shown to have accumulated under stadial or glacial conditions. The possible age of each formation is discussed within the context of evidence provided from the mainland, shelf and deep-sea cores. Two are thought to be pre-Devensian, one is possibly pre-Devcnsian. one is possibly Early and/or Middle Devensian, two are probably Late Devensian, one is Late Devensian to Holocenc and one Present day in age. It is suggested that the Late Devensian ice reached the shelf margin south of the Outer Hebridcan Platform.     

The retreat of the Barents Sea Ice Sheet on the western Svalbard margin

The deglaciation of the continental shelf to the west of Spitsbergen and the main fjord, Isfjorden. is discussed based on sub-bottom seismic records and scdirncnt cores. The sea lloor on the shelf to the west of Isfjorden is underlain by less than 2 m of glaciomarine sediments over a firm diamicton interpreted as till. In central Isfjordcn up to 10 m of deglaciation sediments were recorded, whereas in cores from the innermost tributary, Billefjorden, less than a meter of ice proximal sediments was recognized between the till and the 'normal' Holocene marine sediments. We conclude that the Barents Sea Ice Sheet terminated along the shelf break during the Late Weichselian glacial maximum. Radiocarbon dates from thc glaciomarine sediments above the till indicate a stepwise deglaciation. Apparently the ice front rctrcatcd from the outermost shelf around 14. 8 ka A dramatic increase in the flux of line-grained glaciomarine sediments around 13 ka is assumed to reflect increased melting and/or current activity due to a climatic warming. This second stage of deglaciation was intcrruptcd by a glacial readvance culminating on the mid-shelf area shortly after 12.4 ka. The glacial readvance, which is correlated with a simultaneous readvance of the Fennoscundian ice sheet along the western coast of Norway, is attributed to the so-called 'Older Dryas' cooling event in the North Atlantic region. Following this glacial readvance the outer part of Isljorden became rapidly deglaciated around 12.3 ka. During the Younger Dryas the inner fjord branches were occupied by large outlet glaciers and possibly the ice liont terminated far out in the main fjord. The remnants of the Harcnts Sea Ice Shcet melted quickly away as a response to the Holocene warming around 10 ka.     

Devensian organic interstadial deposits and ice sheet extent in Buchan,Scotland

Pre-Late Devensian organic deposits in the Buchan area of northeast Scotland were investigated for their geomorphological and palaeoecological (pollen, plant macrofossils, coleoptera) properties. Close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of Scandinavia and arctic Russia. The latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method, although the geomorphological and fossil evidence appears to point to an interstadial date within Oxygen Isotope Stages 5a or 5c. The site has special significance for arguments concerning the much-debated concept of ‘Moraineless Buchan’; indeed, evidence is presented which supports the concept of extensive ice sheet glaciation during the Late Devensian for this crucial geographical area. If Buchan is to be seen as a further casualty amongst other disputed ice-free enclaves, then a return to earlier models of extensive ice sheet glaciation in the Late Devensian of Scotland would seem to be necessary. © 1998 John Wiley & Sons, Ltd.     

Lateglacial and Holocene cosmogenic surface exposure age glacial chronology and geomorphological evidence for the presence of cold‐based glaciers at Nevado Sajama,Bolivia

Comparisons of palaeo‐equilibrium line altitudes between the Western and Eastern Cordilleras in the Central Andes are commonly based on the assumption that the tall outermost moraines visible in remotely sensed images of the Western Cordillera date to the Last Glacial Maximum (LGM). However, field investigation and geomorphic mapping at Nevado Sajama, Bolivia, indicates the tall moraines are relic features with shorter moraines overlying and in some cases extending beyond them. ³⁶Cl exposure ages from the shorter moraines suggest that they date to Lateglacial times ca. 16.9–10.2 ka. Although Lateglacial deposits have been found throughout the Central Andes, the extent of these deposits relative to LGM deposits varies both between the Western and Eastern Cordilleras and north‐to‐south along the Western Cordillera. In the Western Cordillera in the zone of easterly winds, the Lateglacial appears to be the most extensive glacial advance of the last glacial cycle. Geomorphic evidence also suggests that some Lateglacial moraines were deposited by cold‐based ice, a previously unreported finding in the tropical Andes. Retreat from other glacial features occurred at about 7.0–4.4 ka and 4.7–3.3 ka. These are the first directly dated Holocene glacial deposits in the Western Cordillera of Bolivia, and their presence suggests that the mid Holocene may not have been as warm and dry as previously thought. Copyright © 2008 John Wiley & Sons, Ltd.