Description: ABSTRACT The southernmost terrestrial extent of the Irish Sea Ice Stream (ISIS), which drained a large proportion of the last British–Irish Ice Sheet, impinged on to the Isles of Scilly during Marine Isotope Stage 2. However, the age of this ice limit has been contested and the interpretation that this occurred during the Last Glacial Maximum (LGM) remains controversial. This study reports new ages using optically stimulated luminescence (OSL) dating of outwash sediments at Battery, Tresco (25.5 ± 1.5 ka), and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on Scilly Rock (25.9 ± 1.6 ka), which confirm that the ISIS reached the Isles of Scilly during the LGM. The ages demonstrate this ice advance on to the northern Isles of Scilly occurred at ∼26 ka around the time of increased ice-rafted debris in the adjacent marine record from the continental margin, which coincided with Heinrich Event 2 at ∼24 ka. OSL dating (19.6 ± 1.5 ka) of the post-glacial Hell Bay Gravel at Battery suggests there was then an ∼5-ka delay between primary deposition and aeolian reworking of the glacigenic sediment, during a time when the ISIS ice front was oscillating on and around the Llŷn Peninsula, ∼390 km to the north. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.

Description: Given current concern about the stability of ice sheets, and potential sea level rise, it is imperative that we are able to reconstruct and predict the response of ice sheets to climate change. The Intergovernmental Panel on Climate Change (IPCC), amongst others, have highlighted that our current ability to do so is limited. Numerical ice sheet models are a central component of the work to address this challenge. An unresolved key issue in this work concerns the volume and rate of ice mass loss needed to explain the large difference between late glacial and interglacial global sea levels. Some 20% of observed sea level rise since the Last Glacial Maximum (LGM) cannot be attributed to any known former ice mass, indicating that this inconsistency arises from the deficiencies in modelled reconstructions of ice sheet volumes and postglacial rebound. Ice sheet models are tested and refined by comparing model predictions of past ice geometries with field-based reconstructions from geological, geomorphological and ice core data. However, on the East Antarctic Ice sheet, Dronning Maud Land (DML) presents a critical gap in the empirical data required to reconstruct changes in ice sheet geometry. In addition, there is poor control on regional climate histories of ice sheet margins, because ice core locations, where detailed reconstructions of climate history exist, are located on high inland domes. This leaves numerical models of regional glaciation history largely unconstrained. MAGIC-DML is a Swedish-US-Norwegian-German-UK collaboration with a focus on filling the critical data gaps that exist in our knowledge of the timing and pattern of ice surface changes on the western Dronning Maud Land margin. Here we describe a series of high-resolution modelling experiments to help identify those areas across western Dronning Maud Land that are the most sensitive to uncertainties in the regional climate history and the choice of model parameters. For this we employ a wide range of climate and ocean histories combining published outputs of 18 general circulation models for the LGM and mid-Holocene with ice core records. The modelling results together with remote sensing mapping of glacial landforms is informing and guiding cosmogenic nuclide sampling campaigns in western Dronning Maud Land starting 2016/17. Successful integration of numerical modelling and field investigations in an iterative manner is key to achieving the anticipated outcome of the MAGIC-DML project, a reconstruction of the long-term pattern and timing of vertical changes in ice surface elevation since the mid-Pliocene warm period, which will provide the missing empirical data required to constrain numerical ice sheet models.

Description: Reconstructing and predicting the response of the Antarctic Ice Sheet to climate change is one of the major challenges facing the Earth Science community. Numerical models of ice sheets are a central component of work to address this challenge, and these models are tested and improved by comparing model predictions of past ice extents with field-based reconstructions (from geological and geomorphological data). However, there are critical gaps in our knowledge of past changes in ice elevation and extent in many regions of East Antarctica, including a large area of Dronning Maud Land. In addition, there exist significant uncertainties in regional climate history along the ice sheet margin due to remoteness of these areas from ice core locations where detailed reconstructions of past climate conditions have been performed. This leaves numerical models of regional glaciation history largely unconstrained. MAGIC-DML is a new Swedish-UK-US-Norwegian-German project that aims to reconstruct vertical changes in ice extent across Dronning Maud Land as the basis for constraining numerical models of ice sheet behavior. The focus of the two planned field seasons will be in areas that have been identified as being critical for differentiating between possible past ice sheet configuration and timing. Geological reconstruction will involve the identification, mapping, and dating of glacially sculpted bedrock, ice-marginal moraines, drift sheets and erratic boulders that provide evidence for past changes in ice levels over thousands to millions of years. Prior to the field investigations, the German team is performing a detailed high-resolution modeling of the paleoglacial history and identifying areas across Dronning Maud Land that are most sensitive to the uncertainties in regional climate history and the choice of model parameters. These modeling results will be used as a basis for planning and guiding the field campaigns in East Antarctica in 2015 and 2016.

Description: Reconstructing and predicting the response of the Antarctic Ice Sheet to climate change is one of the major challenges facing the Earth Science community. There are critical gaps in our knowledge of past changes in ice elevation and extent in many regions of East Antarctica, including a large area of Dronning Maud Land. An international Swedish-UK-US-Norwegian-German project MAGIC-DML aims to reconstruct the timing and pattern of ice surface elevation (thus ice sheet volume) fluctuations since the mid-Pliocene warm period on the Dronning Maud Land margin of the East Antarctic Ice Sheet. A combination of remotely sensed geomorphological mapping, field investigations, surface exposure dating and numerical modelling are being used in an iterative manner to produce a comprehensive reconstruction of the glacial history of Dronning Maud Land. Here we present the results from the first phase of this project, which involves high-resolution numerical simulations of the past glacial geometries and mapping of the field area using historic and recent aerial imagery together with a range of satellite acquired data.

Description: We evaluated the hypothesis that the spatial variation in erosion in a catchment is refl ected in the distribution of the cosmogenic nuclide concentrations in sediments leaving the catchment. Using published data and four new 10Be measurements in fl uvial sediment collected from the outlets of small river catchments, we constrained the spatial variability of erosion rates in the Gaub River catchment in Namibia. We combined these catchment-averaged erosion rates, and the mean slope values with which they are associated, in a digital elevation model (DEM)–based analysis to predict distributions of cosmogenic 21Ne concentrations in the sediment leaving the Gaub catchment. We compared these synthetic distributions with the distribution of concentrations of cosmogenic 21Ne (21NeC) in 32 quartz fl uvial pebbles (16–21 mm) collected from the catchment outlet. The 21NeC concentrations span nearly two orders of magnitude (2.6–160 × 106 atoms/g) and are highly skewed toward low values. The DEM-based analysis confi rms this skew—the measured 21NeC distribution plots within the envelope of distributions predicted for the catchment. This match between measured and synthetic 21Ne distributions implies that the measured distribution is a signature of the spatial variation in erosion rates.

Description: In four rivers in western Scotland for which there is a well-constrained record of relative base-level fall, the rate of postglacial bedrock erosion is quantified by measuring the concentration of in situ cosmogenic 10Be on strath terraces downstrean of headward-retreating knickpoints. Along-channel gradients in 10Be exposure age show two distinct trends: upstream younging and constant age, which we interpret as diagnostic of knickpoint retreat and diffusive transport-limited incision, respectively. We show that bedrock channel incision and regional formation of strath terraces began shortly after deglaciation (ca. 11.5 ka), and that knickpoint retreat rates peaked in the early to mid-Holocene. Erosion rates have since decreased by two orders of magnitude, converging in the late Holocene to low rates independent of stream power per unit channel area. We infer this regional slowing in postglacial knickpoint retreat to be the result of the depletion of paraglacial sediment supply over the Holocene, leading to a deficiency in “tools” for bedrock erosion. Our results imply that episodes of major fluvial erosion may be in tune with glacial cycles, and that sediment depletion following glacial-interglacial transitions may be an important cause of bedrock erosion rate variations in rivers draining glaciated landscapes.

Description: We use a numerical model describing cosmogenic nuclide acquisition in sediment moving through the upper Gaub River catchment to evaluate the extent to which aspects of source area geomorphology and geomorphological processes can be inferred from frequency distributions of cosmogenic 21Ne (21Nec) concentrations in individual detrital grains. The numerical model predicts the pathways of sediment grains from their source to the outlet of the catchment and calculates the total 21Nec concentration that each grain acquires along its pathway. The model fully accounts for variations in nuclide production due to changes in latitude, altitude and topographic shielding and allows for spatially variable erosion and sediment transport rates. Model results show that the form of the frequency distribution of 21Nec concentrations in exported sediment is sensitive to the range and spatial distribution of processes operating in the sediment’s source areas and that this distribution can be used to infer the range and spatial distribution of erosion rates that characterise the catchment. The results also show that lithology can affect the form of the 21Nec concentration distribution indirectly by exerting control on the spatial pattern of denudation in a catchment. Model results further indicate that the form of the distribution of 21Nec concentrations in the exported sediment can also be affected by the acquisition of 21Nec after detachment from bedrock, in the diffusive (hillslope) and/or advective (fluvial) domains. However, for such post-detachment nuclide acquisition to be important, this effect needs to at least equal the nuclide acquisition prior to detachment from bedrock.

Description: Exposure durations of glacial landforms in widely separated areas of central Yukon Territory affected by the northern sector of the Cordilleran Ice Sheet (CIS) and alpine glaciers have been determined using cosmogenic 10Be in quartz. The aim of our research is to test previous reconstructions of glacial history and to begin to address the paucity of chronological control for the lateral and vertical extent of the northern CIS. Chronological evidence for CIS expansion predating the Last Glacial Maximum comes from minimum surface exposure durations of c 100 ka for two bedrock samples within the Reid glacial limit, indicating a possible marine Oxygen Isotope Stage (OIS) 6 age for this event, and from minimum exposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatak within the McConnell glacial limit (OIS 2), indicating a possible OIS 4 age. High elevation minimum surface exposure durations within the McConnell limit indicate that some areas formerly mapped as nunataks were covered by cold-based ice prior to 30 ka. Montane glaciation in the Mackenzie Mountains, outside the McConnell glacial limit, was contemporaneous with nearby CIS advance at 17 ka, with CIS retreat by 15 ka. Deglaciation of the Tintina Trench, a major ice discharge route, was completed by 12 ka. At this time ice in an adjacent discharge route to the south was still entering higher-elevation valleys in the Pelly Mountains. A Lateglacial readvance may have peaked at ca 10 ka in the Ogilvie Mountains. Considerable variation in ages from individual landforms, and possible complex histories, require additional cosmogenic nuclide measurements to confirm interpretations.

Description: Based on cosmogenic 10Be and 26Al analyses in 15 individual detrital quartz pebbles (16e21 mm) and cosmogenic 10Be in amalgamated medium sand (0.25e0.50 mm), all collected from the outlet of the upper Gaub River catchment in Namibia, quartz pebbles yield a substantially lower average denudation rate than those yielded by the amalgamated sand sample. 10Be and 26Al concentrations in the 15 indi- Accepted 9 April 2012 Available online xxx vidual pebbles span nearly two orders of magnitude (0.22 ± 0.01 to 20.74 ± 0.52 x 10 6 10 Be atoms g-1 and 1.35 ± 0.09 to 72.76 ± 2.04 x 106 26Al atoms g-1, respectively) and yield average denudation rates of w0.7 m Myr-1 (10Be) and w0.9 m Myr-1 (26Al). In contrast, the amalgamated sand yields an average Keywords: Beryllium-10 10Be concentration of 0.77 ± 0.03 x 106 atoms g-1, and an associated mean denudation rate of Aluminium-26 Neon-21 Cosmogenic nuclide Grain size bias Namibia 9.6 ± 1.1 m Myr-1, an order of magnitude greater than the rates obtained for the amalgamated pebbles. The inconsistency between the 10Be and 26Al in the pebbles and the 10Be in the amalgamated sand is likely due to the combined effect of differential sediment sourcing and longer sediment transport times for the pebbles compared to the sand-sized grains. The amalgamated sands leaving the catchment are an aggregate of grains originating from all quartz-bearing rocks in all parts of the catchment. Thus, the cosmogenic nuclide inventories of these sands record the overall average lowering rate of the landscape. The pebbles originate from quartz vein outcrops throughout the catchment, and the episodic erosion of the latter means that the pebbles will have higher nuclide inventories than the surrounding bedrock and soil, and therefore also higher than the amalgamated sand grains. The order-of-magnitude grain size bias observed in the Gaub has important implications for using cosmogenic nuclide abundances in deposi- tional surfaces because in arid environments, akin to our study catchment, pebble-sized clasts yield substantially underestimated palaeo-denudation rates. Our results highlight the importance of carefully considering geomorphology and grain size when interpreting cosmogenic nuclide data in depositional surfaces.