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News Article | May 5, 2017
Site: www.eurekalert.org

Central parts of Antarctica's ice sheet have been stable for millions of years, from a time when conditions were considerably warmer than now, research suggests. The study of mountains in West Antarctica will help scientists improve their predictions of how the region might respond to continuing climate change. Its findings could also show how ice loss might contribute to sea level rise. Although the discovery demonstrates the long-term stability of some parts of Antarctica's ice sheet, scientists remain concerned that ice at its coastline is vulnerable to rising temperatures. Researchers from the Universities of Edinburgh and Northumbria studied rocks on slopes of the Ellsworth Mountains, whose peaks protrude through the ice sheet. By mapping and analysing surface rocks -- including measuring their exposure to cosmic rays - researchers calculated that the mountains have been shaped by an ice sheet over a million-year period, beginning in a climate some 20C warmer than at present. The last time such climates existed in the mountains of Antarctica was 14 million years ago when vegetation grew in the mountains and beetles thrived. Antarctica's climate at the time would be similar to that of modern day Patagonia or Greenland. This time marked the start of a period of cooling and the growth of a large ice sheet that extended offshore around the Antarctic continent. Glaciers have subsequently cut deep into the landscape, leaving a high-tide mark - known as a trimline -- in the exposed peaks of the Ellsworth range. The extended ice sheet cooled the oceans and atmosphere, helping form the world of today, researchers say. Their study is among the first to find evidence for this period in West Antarctica. The research, published in Earth and Planetary Science Letters, was done in collaboration with the Scottish Universities Environmental Research Centre. It was funded by the UK Natural Environment Research Council and supported by British Antarctic Survey. Professor David Sugden, of the University of Edinburgh's School of GeoSciences, said: "These findings help us understand how the Antarctic Ice Sheet has evolved, and to fine-tune our models and predict its future. The preservation of old rock surfaces is testimony to the stability of at least the central parts of the Antarctic Ice Sheet -- but we are still very concerned over other parts of Antarctica amid climate change."


News Article | December 7, 2016
Site: www.nature.com

We use new isotopic data, in conjunction with sensitivity tests, a forward model, and other extant records, to evaluate three hypotheses about the behaviour of the East GIS that previous data have not been able to address conclusively. For the past 7.5 Myr, we test whether (1) East GIS behaviour mirrored global climate/ice volume as represented by the marine δ18O record; (2) the efficacy of erosion under the East GIS varied over time and space; (3) most interglacial periods were sufficiently short-lived or cool enough that they did not cause notable reductions in East GIS extent. Most of what is known about long-term ice-sheet history comes from marine sediment records interpreted as global or regional proxies for ice volume or glacial activity. For example, stable oxygen isotope measurements of foraminifera isolated from marine sediment track global ice volume and ocean temperature, but provide little information about the individual behaviour of each of the world’s major ice sheets20. Global sea-level history reflects total ice volume, but in a complex fashion30 because the record is aliased by local tectonic and glacio-isostatic adjustment of land levels31. The most robust inferences about the comings and goings of now-vanished ice sheets are based on the presence and provenance in marine sediment of IRD shed from melting icebergs that originated on glaciated continents2, 8. IRD records are illustrative of when sediment-bearing glacial ice reached the coast, but with few exceptions32 do not otherwise constrain ice extent33. Figure 1 presents our compilation of references relevant to understanding the history of ice on Greenland since the Miocene. References for Fig. 1 are cited in Extended Data Fig. 5. Making accurate inferences about ice-sheet behaviour on the basis of terrestrial sediment recovered from marine archives requires knowledge of the sediment source area. Multiple lines of evidence indicate that the quartz we isolated was sourced from East Greenland. The East Greenland Current (Fig. 3) drifts icebergs from north to south over both Sites 918 and 987, which suggests that the IRD we analysed is dominantly from East Greenland34. IRD composition downcore at Site 918 consistently indicates eastern Greenland sediment sourcing for millions of years35, 36, 37. While there may be some contribution from gravity flows off the continental shelf, sedimentological evidence suggests that most sand at Site 918 comes from ice rafting rather than turbidites6, 19, 38, 39. At Site 918, sand is compositionally similar to larger dropstones, which is consistent with an IRD source for the sand40. Sediment at Site 987 is probably more locally sourced because drilling was done on the toe of a large subaqueous fan5; although some of the Site 987 sediment may come from the north, most was presumably delivered directly from ice flowing east through Scoresby Sund (Fig. 3). In summary, the cosmogenic data we present reflect the history of and processes active in eastern Greenland. Thermal conditions at the base of the ice sheet are not well known and change over time41 and space23, 42. Warm-based ice (the ultimate source of the sediment we analysed because it is required to erode the material) is most likely to be found in deep troughs, near some ice margins, and where geothermal heat flux is high23, 43, 44. Models suggest that 20% to 30% of the pre-industrial Holocene GIS was warm-based43, but during the Last Glacial Maximum up to 50% of ice on Greenland may have been warm-based, perhaps due to increased thickness41. Because cosmogenic nuclides with different half-lives decay at different rates after production ceases, multiple nuclides can be measured in tandem (for example, 10Be and 26Al) to provide insight about periods of burial. A multi-nuclide approach can thus constrain the timing and duration of burial by non-erosive, cold-based ice45, which is a process that has probably occurred variably in Greenland over both space and time. When exposure begins on a fresh surface, the 26Al/10Be ratio is the production ratio of the two nuclides. If a previously exposed surface is buried and shielded from further nuclide production, the 26Al/10Be ratio drops because the 0.71-Myr half-life of 26Al (ref. 46) is shorter than the 1.39-Myr half-life of 10Be (refs 47, 48, 49). If a sample is exposed again following burial, production resumes and the 26Al/10Be ratio increases because the production rate of 26Al is greater than that of 10Be. It is important to note that relatively short burial durations (<100–200 kyr) and/or re-exposure following burial can result in 26Al/10Be ratios that are indistinguishable from the production ratio24, 50 even though the surface has experienced periods of burial lasting tens of thousands of years. Any inferences stemming from 26Al/10Be ratios are largely dependent upon the assumed 26Al/10Be production ratio, which is a direct function of the production rates of the two nuclides. Although nuclide production rates have long been known to vary across latitude and elevation11, 51, it has generally been assumed that 10Be and 26Al production rates scale similarly, with a resulting production ratio of 6.75 for all locations on Earth’s surface28. However, recent work has suggested that the production ratio is itself dependent on latitude and elevation because each isotope’s production rate scales differently across space52, 53, 54. Argento et al.52 used numerical models to estimate a 26Al/10Be production ratio of 7.0 to 7.1 at sea level and high latitude, which is in agreement with the median value of 7.16 calculated from low-elevation (<2,000 m) calibration samples presented in the same study. Sites from a range of latitudes and elevations have production ratios ranging from 7.0 to 7.3, scaled to sea level and high latitude, and using seven different scaling schemes54. Atmospheric mass drives the differences in production between nuclides, with elevation probably being more important than latitude55, although comprehensive studies of the global variation in the 26Al/10Be production ratio have not yet been conducted. In this study, we place more emphasis on the relative rather than the absolute 26Al/10Be ratio in marine sediment over time; hence the assumed 26Al/10Be production ratio is less important here than in studies inferring absolute exposure and burial durations. However, we base our assumed production ratio on the work of Corbett et al.56, who quantified 26Al/10Be in 24 continuously exposed bedrock and boulder surfaces at four high-latitude sites in Greenland that were deeply eroded during the last glaciation. They determined a 26Al/10Be production ratio of 7.3 ± 0.3 (slope of a York linear regression fit to all data with errors in both variables, 1σ), supporting recent modelling work indicating that the production ratio can exceed 6.75 at locations such as Greenland. Although the geographic variability of the production ratio is still unclear, we choose to employ the production ratio of ref. 56 here because the source of the sediments from Sites 918 and 987 is similar to the latitude range of the calibration samples in their data set. We measured 10Be in 30 samples and 26Al in 22 samples spanning the last 7.5 Myr and 2.6 Myr, respectively, in sediment cores at Site 918, located in the Irminger basin 110 km southeast of Greenland (63.1° N, 38.6° W, 1,800 m water depth). This site was previously used to define the onset of Greenland glaciation on the basis of the earliest occurrence of IRD6, which is included in our oldest sample. We also measured 10Be in 16 samples from Site 987 spanning the last 2.2 Myr of deposition 130 km offshore of Scoresby Sund and 1,200 km northeast of Site 918 (70.5° N, 17.9° W, 1,670 m water depth)57. Core samples were obtained from the Bremen Core Repository. We disaggregated and wet-sieved sediments isolating the grain size fraction 0.125–0.750 mm and used weak acid ultrasonic leaching (0.25% to 0.5% HF and HNO ) to slowly dissolve all minerals other than quartz58. We amalgamated quartz from subsamples taken over an interval of core until we had sufficient quartz mass (7.8 g to 25.3 g) from which to extract and reliably measure 10Be. Thus, samples represent the average 10Be content of quartz present in core sections ranging in length from 0.04 m to 91 m (median 6 m, standard deviation 19 m). All uncertainties reported in this paper are 1σ. Age spans for samples range from 0.001 Myr to 2.9 Myr (median 0.1 Myr, standard deviation 0.5 Myr). Our marine sediment record of 10Be and 26Al concentrations does not have the temporal resolution to clearly reflect major high-frequency changes in Plio-Pleistocene climate, such as the major interglacials at MIS 11, MIS 9 or MIS 5e. The need to amalgamate sufficient quartz for measuring very low isotope abundances meant that integration of core sediment over depth (and thus time) mixed sand deposited during glacial and interglacial periods; analysis of a core more proximal to the continental shelf might overcome this limitation. After purifying quartz, samples were dissolved using HF in the presence of 9Be carrier produced from beryl. Samples were processed in batches of 12 including two full chemistry process blanks59. 10Be measurements were made at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory60, 61 and referenced to standard 07KNSTD3110 (ref. 46) assuming a 10Be/9Be ratio of 2,850 × 10−15. 26Al measurements were made at the Scottish Universities Environmental Research Centre62 and normalized to the Z92-022246 standard with a nominal 26Al/27Al ratio of 4.11 × 10−11. The average blank ratio (10Be/9Be = (4.6 ± 1.0) × 10−16, n = 6; group 1, 26Al/27Al = (8.5 ± 2.1) × 10−16, n = 4; group 2 26Al/27Al = (14.9 ± 4.5) × 10−16, n = 4) was subtracted from measured ratios, and uncertainties in sample and blank ratios were propagated in quadrature (Supplementary Table 1). Replicate preparation of sample 918-17 (918-17X) indicates reproducibility within measurement uncertainty (Supplementary Table 1). Statistically identical measured concentrations of 10Be in four samples (987-E to 987-H) collected from different depths in a 70-cm-thick IRD-rich layer (4,250 ± 370 to 4,460 ± 300 atoms g−1) also demonstrate the reproducibility of our measurements (Supplementary Table 1). In all samples, measured 10Be concentrations are low (2,100 to 40,000 atoms g−1), but well above procedural backgrounds. Because of the shorter half-life of 26Al, it is detectable only in younger samples (<2.6 Myr), and was measured only at Site 918; concentrations of 26Al are also low (9,700 to 118,000 atoms g−1; Supplementary Table 1), but similarly well above background. Cosmogenic 26Al/10Be ratios at the time of deposition (corrected by core depth–age models) range from about 3.9 to about 7.5 (Supplementary Table 1). For Site 918, we used established age–depth constraints from ref. 19, who applied ages from the timescale of ref. 63 to magnetostratigraphic64 and biostratigraphic datums65, 66. Ages were linearly interpolated between these control points (Extended Data Fig. 1). Note that there is an erosional hiatus at 71.1 m below the seafloor, which is estimated to span 1.71–1.39 Myr19. We also developed a planktonic δ18O record (N. pachyderma, left-coiling) to refine the age model above the Brunhes–Matuyama reversal (780 kyr) at 45.9 m below the seafloor64. 168 stable isotope measurements were made at the Lamont–Doherty Earth Observatory, and 11–15 tests were used per sample. The δ18O record clearly displays the Holocene and the last interglacial, but there is some ambiguity in the identification of other marine isotope stages, such as MIS 11 and MIS 13 (Extended Data Fig. 2). For Site 987, we developed an age model by linearly interpolating between the age control points reported by the Leg 162 shipboard scientific party57, which are primarily based on palaeomagnetic events (Extended Data Fig. 1). Measured 10Be and 26Al concentrations (Supplementary Table 1) were corrected for decay since deposition on the seafloor using these age models and assuming half-lives of 10Be t  = 1.39 Myr (ref. 49) and 26Al t  = 0.71 Myr (ref. 67). Since our cosmogenic-nuclide samples were amalgamated from subsamples spanning 0.001 Myr to 2.9 Myr (Supplementary Table 3), we used the sand mass-weighted mean age of these subsamples to derive a single integrated age for each cosmogenic sample. Age model uncertainties can alter the absolute value of decay-corrected 10Be concentrations and change the timing of some isotopic shifts, but have minimal impact on the overall structure of the record. We examined the sensitivity of 10Be concentrations and 26Al/10Be ratios to erosion, burial, exposure and mixing (Fig. 2), assuming sea-level high-latitude production rates, including production from muons calculated using the MATLAB implementation13, 28. Depth profiles were first run to secular equilibrium, which was reached when nuclide production balanced loss via radiodecay and erosion; the latter was simulated by shifting the profile upward each time step in proportion to the prescribed ice-free surface erosion rate (5 m Myr−1, 20 m Myr−1 or 50 m Myr−1). Steady-state profiles with higher erosion rates have lower 10Be concentrations because nuclides are shed more rapidly, but they have higher 26Al/10Be ratios because nuclides are brought to the surface more quickly and thus have less time to decay in the subsurface (Fig. 2a). We simulated cold-based ice cover for 1 Myr by halting production and allowing the 20 m Myr−1 steady-state profile to decay in place without additional sub-ice erosion, whereas an analogous simulation for warm-based ice cover continued to erode under ice at 20 m Myr−1. Surface nuclide concentrations decrease much faster under the erosive warm-based ice, and 26Al/10Be ratios also decline more quickly since the erosive ice brings deeper-buried (and thus longer-buried) nuclides to the surface. The 1-Myr-long warm-based ice simulation was performed again, but interrupted by either a 10-kyr or 200-kyr episode of interglacial exposure (with ice-free surface erosion continuing at 20 m Myr−1) halfway through the simulation. In these simulations, because nuclide concentrations were very low before the interglacials, both were able to quickly reset the 26Al/10Be ratio to pre-glacial values; however, only the very long (200 kyr) interglacial had sufficient time to fully rebuild nuclide concentrations. Lastly, we modelled the mixing of sediment from low-concentration, low-ratio (eroded and long-buried) and high-concentration, high-ratio (long-exposed) endmembers to understand how the values we measured in marine sediments might reflect contributions from multiple source areas on Greenland. Nuclide concentrations mix linearly: C  = C F  + C F , where C and C and F and F are the nuclide concentrations and mixing fractions (F  + F  = 1) of the two endmembers. 26Al/10Be ratios, however, exhibit nonlinear mixing that is weighted by the ratio of the endmembers’ nuclide concentrations, because the greater the number of nuclides one endmember contributes relative to the other, the more it influences the mixed nuclide ratio: R  = R (C F /(C F  + C F )) + R (C F /(C F  + C F )). Our sensitivity tests demonstrate how progressively deeper erosion, interglacial exposure, burial by cold-based ice, and sediment mixing from different sources affect the concentration of 10Be and 26Al in terrestrial sediment exported from Greenland (Fig. 2). Such modelling shows that covering a landscape with non-erosive, cold-based ice for hundreds of thousands of years lowers the 26Al/10Be ratio, but does not much change 10Be concentration because of the long half-life of 10Be in relation to the burial duration (Fig. 2b). In contrast, cover by erosive, warm-based ice not only lowers the 26Al/10Be ratio by shielding the bed from cosmic ray exposure, but also lowers nuclide concentrations because it erodes material with previously produced nuclides and incorporates rock or sediment that was once deeply shielded from cosmic radiation. After the upper several metres of rock and soil are eroded by warm-based ice, isotopic concentrations in the resulting sediment are low and relatively insensitive to continued erosion. This is because the concentration of 10Be in sediment produced by glaciers is controlled primarily by the extent of sub-ice erosion into the deep, muon-dominated production zone that extends tens of metres below the pre-glacial land surface where nuclide concentration changes only gradually with depth (Fig. 2a). When sediment is the result of mixing of components with different burial and erosion histories, the history of the sediment may be constrained by considering possible end members with different nuclide concentrations and 26Al/10Be ratios, mixed in different proportions (Fig. 2d). The 10Be concentrations we measured reflect the erosion-weighted average 10Be concentration of the areas from which they were sourced, while 26Al/10Be ratios are biased towards source areas that had relatively high nuclide concentrations. To better constrain the interpretation of cosmogenic-nuclide measurements in marine sediment, we collected sediment samples from Greenlandic rivers, moraines and river terraces and measured their 10Be (ref. 18), and in some cases, 26Al concentrations (Supplementary Table 2). Sediment sourced from the ice sheet in eastern, western and southern Greenland both today18 and at the end of the last glaciation (sampled in well-dated terraces)18, 21 has very low concentrations of 10Be of only thousands of atoms per gram. Sediment in streams draining only areas outside the current ice margin has on average several times more 10Be, which reflects exposure of the land surface to cosmic radiation during the Holocene18. Isotope and mass balance calculations indicate that most sediment now being delivered to the Greenlandic margin originates from beneath the ice sheet and not from the deglaciated margin18. To complement existing 10Be data18, we measured 26Al in four samples of contemporary river sediment as well as sediment from the Keglen Delta terrace at Kangerlussuaq26 (sample GLX-08) and another terrace deposited near Narsarsuaq68 (GLX-34). Sediment in the Keglen Delta was deposited during the deglaciation (about 7 kyr ago)26 and has a 26Al/10Be ratio substantially lower than the production ratio (GLX-08, 4.54 ± 0.58, 1σ). All sediment from modern streams, as well as that in the terrace at Narsarsuaq (GLX-34) deposited during a neoglacial readvance about 1.5 kyr (after mid Holocene retreat and exposure of the now mostly ice-covered landscape)68, has an average ratio of 7.62 ± 2.12 (1σ; n = 5), similar to the production ratio. These data imply that at deglaciation, sediment leaving the ice sheet about 7 kyr ago had an 26Al/10Be ratio lower than the production value, and that exposure during the mid-Holocene, when the GIS retreated a few to tens of kilometres inland of the current margin, raised the 26Al/10Be to or near that of production, as suggested by our sensitivity tests (Fig. 2). These results imply that short periods (about 10–20 kyr) of subaerial interglacial exposure, primarily at the margins of the ice sheet, matter little because they change the nuclide concentration substantially only in the uppermost few metres of rock or soil via shallow neutron spallation reactions. However, even short interglacial re-exposure can effectively raise the 26Al/10Be ratio if initial nuclide concentrations are very low when exposure begins (Fig. 2c). The glacial sediment system itself may limit the resolution of the record. Sediment tracing using 10Be unambiguously shows that most sediment delivered to the current-day Greenland margin during the Holocene interglacial is derived from under the ice, has very little 10Be and 26Al, and is not sourced from the deglaciated peripheral area18. Sediment currently being shed from deglaciated terrain has concentrations of 10Be several times higher than that of glacially derived material, but the marginal area is small in comparison to the area still covered by ice18. During glacial advances, sediment from previously exposed margins will be incorporated by ice and eventually mixed with long-shielded material and moved offshore. Even though the marginally sourced material has higher concentrations of 10Be, it is overwhelmed volumetrically by material coming from areas that have been long covered by ice and thus limits the marine record’s sensitivity to interglacial cosmic-ray exposure. We determined a pre-glacial erosion rate for southeast Greenland from the decay-corrected 10Be concentration in our oldest sample at Site 918 (135,000 ± 10,900, 1σ; Supplementary Table 1), which integrates sediments from the 20 m of core immediately below the oldest dropstone at Site 918 identified by ref. 6. Assuming the 10Be in this sample was produced at the surface at sea level directly onshore from Site 918 and experienced no topographic shielding, we obtain an erosion rate of approximately 22 ± 3 m Myr−1 using the CRONUS calculator v.2.328. This estimate is relatively insensitive to these assumptions, except for elevation, which would, for instance, double the erosion rate if production occurred at 1,000 m above sea level rather than at sea level. We measured Site 918 sand (>63 μm) content and binned data over the same depth intervals as the 10Be samples to facilitate comparison. We similarly binned values in the marine benthic δ18O record29 over the same time intervals as the Site 918 10Be record. Regressions, using logarithmic scaling for the Site 918 10Be and sand records, show pronounced relationships, with lower 10Be associated with higher sand content and more enriched marine δ18O (r2 = 0.52 in both cases, P < 0.001) (Extended Data Fig. 3). As Site 918 sand concentrations probably reflect glacial erosion on land and marine δ18O is a proxy for global ice volume, these relationships are broadly consistent with intensified glacial activity yielding lower 10Be concentrations in East-Greenland-derived sediments. As a first-order attempt to reproduce the Sites 918 and 987 cosmogenic-nuclide records, we constructed a simple model of GIS dynamics and cosmogenic-nuclide concentrations driven by three different plausible ice volume reconstructions over the past 5.3 Myr. The model consists of two sets of ten parallel cosmogenic-nuclide depth profiles, as described in Methods section ‘Sensitivity tests’, and was initialized using 20 m Myr−1 ice-free surface erosion rate steady-state nuclide depth profiles reflecting pre-ice-sheet conditions as indicated by the deepest sample in Site 918. Ice sheet extent was modelled from 0% to 100% in 10% increments by turning nuclide production on or off for the corresponding number of depth profiles at a given time step; for example, production was on for all depth profiles when ice cover was 0%, but for only nine profiles when ice cover was 10%, and so on. The time step is 2 kyr. Since the actual GIS extent through time is poorly constrained, we tried parameterizing it with three different time series: a sea-level record derived from δ18O variations in the semi-enclosed Mediterranean Sea basin69, the marine δ18O record of global ice volume and deep ocean temperature20, and a simulated history of the GIS from an ice-sheet model forced by the marine δ18O record70. The last time series explicitly gives ice-sheet extent; the relationship between the first two series and GIS extent was calibrated by assuming that ice cover was 100% at 12 kyr, 80% today, 50% during MIS 11, 20% during the mid-Pliocene, and 0% in the Miocene. We used a simple formulation of basal temperature regimes beneath the modelled ice. Because the GIS has roughly equal areas of cold- and warm-based ice today44, we set the modelled ice cover also to have equal fractions by making one set of depth profiles warm-based (sub-ice erosion rate 20 m Myr−1) and the other set cold-based (sub-ice erosion rate 0 m Myr−1). Spatial variability in basal temperature regimes was introduced by switching between the warm-based and cold-based regime of the two sets of depth profiles every 500 kyr; this is not meant to be realistic, but rather simply to help assess the role of this variable in driving cosmogenic-nuclide concentrations given that the basal thermal history of the GIS is not known. Erosion rates were 20 m Myr−1 in ice-free areas. The simulated cosmogenic-nuclide values shown in Extended Data Fig. 4 represent the material shed from ice-covered, warm-based depth profiles in the model, and assume instantaneous transport to the deep sea. This forward modelling illustrates the limitations in the approach we present here as well as the uncertainty of assumptions underlying the model (Extended Data Fig. 4). Our model reproduces the overall 10Be record for both Sites 918 and 987, but does not capture the fine structure of the Site 918 data. The ice-sheet extent from a model simulation70 consistently underestimates 10Be and 26Al/10Be, probably because it does not accurately reflect GIS dynamism in the Pleistocene. The marine δ18O proxy20 and sea-level proxy69 generate more realistic 26Al/10Be; the sea-level proxy generates the best fit to the 10Be record. We interpret the fine structure (10Be peaks at 2.5 Myr, 1.9 Myr and 1.1 Myr), which we cannot model, as changes in the sediment source area to which cosmogenic nuclides are singularly sensitive; most likely these peaks represent expansion of warm-based areas of the ice sheet into terrain that had not previously been eroded. The MATLAB code files used to generate the forward model are available at https://github.com/shakunj/Bierman-et-al-2016-Nature. The three versions of the model are provided as MATLAB code files with the forcing series representing GIS extent through time designated in the model file name (forward_model_XXXXX.mat). These input driving series are the deep-sea δ18O record20 (LR04.mat), the Mediterranean Sea sea-level record69 (med.mat), and simulated ice sheet extent based on modelling70 (deboer.mat), all given at 2-kyr resolution over the past 5.3 Myr. Initialized bedrock profiles with steady-state 10Be and 26Al concentrations at 1-cm depth increments below the surface assuming a sea-level high-latitude production rate and 20 m Myr−1 ice-free surface erosion rate are given in steadystate_10Be_20mMyr.mat and steadystate_26Al_20mMyr.mat. Sea-level high-latitude 10Be and 26Al production rates in 1-cm depth increments below the surface are given in P10.mat and P26.mat. The file er_half_Ma.mat determines which set of bedrock profiles are beneath erosive warm-based ice (1) or non-erosive cold-based ice (0) at each time step. All data generated and analysed during this study are included in this Letter and its Supplementary Information. MATLAB forward-model code is available at https://github.com/shakunj/Bierman-et-al-2016-Nature.


News Article | November 17, 2016
Site: news.europawire.eu

DUNDEE, 17-Nov-2016 — /EuropaWire/ — The University of Dundee announced today that it is a Grand Challenges Explorationswinner, an initiative funded by the Bill & Melinda Gates Foundation. The project will enable a unique collaboration bringing together expertise at Dundee in male fertility and drug discovery to help identify possible new male contraceptive drugs. Grand Challenges Explorations (GCE) supports innovative thinkers worldwide to explore ideas that can break the mold in how we solve persistent global health and development challenges. The Dundee project, led by Professor Andrew Hopkins (Chair of Medicinal Informatics), Dr Paul Andrews (Director of Operations, National Phenotypic Screening Centre) and Professor Christopher Barratt (Chair of Reproductive Medicine and Director of the Reproductive Health Unit) is one of more than 55 Grand Challenges Explorations Round 17 grants announced today by the Bill & Melinda Gates Foundation. To receive funding, the Dundee team and other Grand Challenges Explorations winners demonstrated in a two-page online application a bold idea in one of six critical global heath and development topic areas. The foundation will be accepting applications for the next GCE round in February 2017. Professor Barratt said, “This unique collaboration at the University of Dundee will begin to address an unmet medical and societal need for new male contraceptive drugs.” Dr Andrews said, “The Grand Challenges Exploration funding will allow the development of high throughput imaging to measure the motility of human sperm and assess their functional readiness to penetrate the egg – both key aspects of sperm behavior (or “phenotype”) that are required for fertility. Once established, the assay platform will be used to screen large chemical libraries for agents that render sperm incapable of fertilisation.” Professor Hopkins added, “This collaboration combines the male fertility expertise in the School of Medicine at the University and the world-class facilities we have at the National Phenotypic Screening Centre, which is based within the School of Life Sciences.” Grand Challenges Explorations is a US$100 million initiative funded by the Bill & Melinda Gates Foundation. Launched in 2008, over 1228 projects in more than 65 countries have received Grand Challenges Explorations grants. The grant program is open to anyone from any discipline and from any organization. The initiative uses an agile, accelerated grant-making process with short two-page online applications and no preliminary data required.  Initial grants of US$100,000 are awarded two times a year. Successful projects have the opportunity to receive a follow-on grant of up to US$1 million. The University of Dundee is one of the world’s top 200 universities and in 2016 was named Scottish University of the Year for the second consecutive year (Sunday Times Good University Guide). Dundee is internationally recognised for the quality of its teaching and research and has a core mission to transform lives across society. Both Times Higher Education and QS World University Rankings have ranked Dundee best in the UK and one of the top 20 worldwide among universities under 50 years old. Our students also rate us very highly on student satisfaction – we are one of the UK’s top ten in the National Student Survey 2016, and first for personal development of students. Dundee is the top ranked University in the UK for biological sciences, according to the 2014 Research Excellence Framework, the major assessment of research quality. See www.dundee.ac.uk for further details. The National Phenotypic Screening Centre (NPSC) was set up by the Scottish Universities Life Science Alliance (SULSA) with a £8M capital funding from the Scottish Government to provide state-of-the-art capabilities in the development and screening of physiologically-relevant assays for academia and allow close collaboration with industry. The main facility is in newly-refurbed labs within the School of Life Sciences at the University of Dundee (working closely with other labs at the Universities of Edinburgh and Oxford). The NPSC has world-class high throughput imaging platforms that can be applied to human, animal, and plant health challenges. More details can be found at www.npsc.ac.uk For media enquiries contact: Roddy Isles Head of Corporate Communications University of Dundee Nethergate, Dundee, DD1 4HN Tel: +44 (0)1382 384910 Mobile: 07800 581902 Email: r.isles@dundee.ac.uk


Blamey N.J.F.,Brock University | Blamey N.J.F.,University of Aberdeen | Parnell J.,University of Aberdeen | McMahon S.,University of Aberdeen | And 8 more authors.
Nature Communications | Year: 2015

The putative occurrence of methane in the Martian atmosphere has had a major influence on the exploration of Mars, especially by the implication of active biology. The occurrence has not been borne out by measurements of atmosphere by the MSL rover Curiosity but, as on Earth, methane on Mars is most likely in the subsurface of the crust. Serpentinization of olivine-bearing rocks, to yield hydrogen that may further react with carbon-bearing species, has been widely invoked as a source of methane on Mars, but this possibility has not hitherto been tested. Here we show that some Martian meteorites, representing basic igneous rocks, liberate a methane-rich volatile component on crushing. The occurrence of methane in Martian rock samples adds strong weight to models whereby any life on Mars is/was likely to be resident in a subsurface habitat, where methane could be a source of energy and carbon for microbial activity. © 2015 Macmillan Publishers Limited. All rights reserved.


Boyce A.,Scottish Universities | Parnell J.,University of Aberdeen
Planet Earth | Year: 2010

Adrian Boyce and John Parnell examine whether traces of life be found in the harshest conditions on Mars. The Haughton impact crater lies in the wilderness of the Canadian High Arctic on Devon Island - the largest uninhabited island on Earth. Nearly 40 million years ago, a meteorite two kilometers across crashed into Earth, leaving behind a 23km-wide crater in the bedrock and causing serious damage over an area of 50km 2. The rocks the meteorite encountered were mainly ancient carbonates, around 470 million years old, but they also contained thick beds of sulphate salts, called gypsum. These are the remnants of ancient seas and lakes that dried up, of which there are many examples through geological time. The occurrence of sulphate also sparks an intriguing possibility. Sulphate is at the heart of one of the oldest and most important biological metabolic functions on Earth - bacterial sulphate reduction.


Researchers from the Scottish Universities Environmental Research Centre (SUERC) found a new way to determine the outcome of stored carbon dioxide (CO2) emissions. The increasing levels of global warming continue to pose risks such as massive wildfires and extensive droughts. CO2 byproduct from coal burning and other energy generation processes add to the accumulative global warming rate and its effects. Carbon capture and storage (CCS) refers to the process of storing CO2 in abandoned gas and oil fields. Deep aquifers - water-bearing rocks found underground - were also identified as an alternative storage unit. Trapping CO2 emissions underground will help prevent the greenhouse gas from getting to the atmosphere. Scientists claim that a general usage of CCS in the next few years will help in the reduction of CO2 emission levels and, ultimately, slow down global warming. The research team used gas samples from the wells at the Cranfield enhanced oil recovery field in Mississippi in southern America. They focused on samples taken in 2009 and 2012. A 'fingerprinting' process enables the scientists to study 'unique signatures' from noble gasses such as neon, helium and argon to monitor potential CO2 movement. The paper's co-author, Professor Finlay Stuart from SUERC University of Glasgow, expressed that the research proved how the noble gases in the injected CO2 can be used as fingerprints. The finding is first of its kind. By looking at the gases' unique signatures, scientists can then monitor the CO2 and how it was disposed. Stuart explained the huge potentials of CCS as a CO2 mitigation method. However, before CCS can develop into a widespread CO2 storage process, further research is needed to determine the effectivity of stowing the greenhouse gas underground. Noble gases such as neon, helium and argon are chemically inactive. Its interaction with water and rocks will have no effect in its activity. This level of inactivity can help identify the physical procedures that altered CO2 and determine its fate. The study's co-author Dr. Stuart Gilfillan from the University of Edinburgh, expressed that the findings is beneficial to large-scale fingerprints in future CCS projects. "This study now shows that these fingerprints can be used to track the movement and fate of injected CO₂ over much shorter periods relevant to CCS," said Gilfillan. The research was funded by the Engineering and Physical Sciences Research Council in the United Kingdom. Researchers published their paper in the International Journal of Greenhouse Gas Control on Sep. 29, 2015. The University of Glasgow released the study findings online on Oct. 5, 2015.


Humphreys M.P.,University of Southampton | Achterberg E.P.,University of Southampton | Achterberg E.P.,Leibniz Institute of Marine Science | Griffiths A.M.,University of Southampton | And 2 more authors.
Earth System Science Data | Year: 2015

The stable carbon isotope composition of dissolved inorganic carbon (δ13CDIC) in seawater was measured in a batch process for 552 samples collected during two cruises in the northeastern Atlantic and Nordic Seas from June to August 2012. One cruise was part of the UK Ocean Acidification research programme, and the other was a repeat hydrographic transect of the Extended Ellett Line. In combination with measurements made of other variables on these and other cruises, these data can be used to constrain the anthropogenic component of dissolved inorganic carbon (DIC) in the interior ocean, and to help to determine the influence of biological carbon uptake on surface ocean carbonate chemistry. The measurements have been processed, quality-controlled and submitted to an in-preparation global compilation of seawater δ13CDIC data, and are available from the British Oceanographic Data Centre. The observed δ13CDIC values fall in a range from g-0.58 to +2.37 ‰, relative to the Vienna Pee Dee Belemnite standard. The mean of the absolute differences between samples collected in duplicate in the same container type during both cruises and measured consecutively is 0.10 ‰, which corresponds to a μ uncertainty of 0.09 ‰, and which is within the range reported by other published studies of this kind. A crossover analysis was performed with nearby historical δ13CDIC data, indicating that any systematic offsets between our measurements and previously published results are negligible. Data doi.org/10.5285/09760a3a-c2b5-250b-e053-6c86abc037c0 (northeastern Atlantic), doi.org/10.5285/09511dd0-51db-0e21-e053-6c86abc09b95 (Nordic Seas). © Author(s) 2015. CC Attribution 3.0 License.


Guilbaud R.,University of Edinburgh | Ellam R.M.,Scottish Universities | Butler I.B.,University of Edinburgh | Gallagher V.,Scottish Universities | Keefe K.,Scottish Universities
Journal of Analytical Atomic Spectrometry | Year: 2010

We have developed a procedure for iron isotope analysis using a hexapole collision cell MC-ICP-MS which is capable of Fe isotope ratio analysis using two different extraction modes. Matrix effects were minimised and the signal-to-background ratio was maximised using high-concentration samples (∼5 μg Fe) and introducing 1.8 mL min-1 Ar and 2 mL min -1 H2 into the collision cell to decrease polyatomic interferences. The use of large intensity on the faraday cups considerably decreases the internal error of the ratios and ultimately, improves the external precision of a run. Standard bracketing correction for mass bias was possible when using hard extraction. Mass bias in soft extraction mode seems to show temporal instability that makes the standard bracketing inappropriate. The hexapole rf amplitude was decreased to 50% to further decrease polyatomic interferences and promote the transmission of iron range masses. We routinely measure Fe isotopes with a precision of ± 0.05‰ and ± 0.12‰ (2σ) for δ56Fe and δ57Fe respectively. © 2010 The Royal Society of Chemistry.


Bryant C.,Scottish Universities
Planet Earth | Year: 2012

Charlotte Bryant explains how bat and bird droppings helped scientists reconstruct 40,000 years of climate history and species evolution in south-east Asia. Researchers Chris Wurster and Michael Bird have spent many years sampling guano deposits in the caves of south-east Asia, and tales of their fieldwork are enough to put anyone off joining them. Fortunately, given the less-than-savory conditions, the sampling process simply involves digging a pit. But you could be forgiven for asking why anyone would willingly venture into such an environment more than once. One particular conundrum that guano has proved invaluable in solving involves the biodiversity of south-east Asia. This region is characterized by many small and some very large islands, separated by shallow continental seas or deep oceanic trenches. Changes in sea level have produced the many different sizes of these islands and affected the way they are connected together and to mainland Asia.


Garnett M.,Scottish Universities
Planet Earth | Year: 2010

Researchers at the NERC Radiocarbon Facility (Environment) in East Kilbride, Scotland, have developed an innovative kit to sample carbon dioxide using a clay sieve. Carbon dioxide is important to many processes that occur on Earth, a component of our planet's atmosphere and, in terms of climate change, one of the most important greenhouse gases. The rate that carbon cycles through these various routes before returning to the atmosphere as carbon dioxide has a critical influence on its concentration in the atmosphere. This is because the amount of carbon in the Earth's atmosphere is small compared to that in the oceans and on land. Zeolite is a rather unimpressive looking clay material which has remarkable properties. Firstly, it contains a uniform network of tiny pores which allow small molecules including carbon dioxide to pass through but exclude larger molecules.

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