Seasonal variations in Greenland Ice Sheet motion : Inland extent and behaviour at higher elevations

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Subglacial Drainage Evolution Modulates Seasonal Ice Flow Variability of Three Tidewater Glaciers in Southwest Greenland

B.J.D was funded in the form of a PhD studentship provided by the Scottish Association for Geosciences, Environment and Society (SAGES) and the University of St Andrews, UK. J.M.L is supported by a UKRI Future Leaders Fellowship (Grant No. MR/S017232/1). D.F would like to acknowledge the support of this work through the EPSRC and ESRC Centre for Doctoral Training on Quantification and Management of Risk and Uncertainty in Complex Systems Environments Grant No. (EP/L015927/1).Surface‐derived meltwater can access the bed of the Greenland Ice Sheet, causing seasonal velocity variations. The magnitude, timing and net impact on annual average ice flow of these seasonal perturbations depends on the hydraulic efficiency of the subglacial drainage system. We examine the relationships between drainage system efficiency and ice velocity, at three contrasting tidewater glaciers in southwest Greenland during 2014‐2019, using high‐resolution remotely sensed ice velocities, modelled surface melting, subglacial discharge at the terminus and results from buoyant plume modelling. All glaciers underwent a seasonal speed‐up, which usually coincided with surface melt‐onset, and subsequent slow‐down, which usually followed inferred subglacial channelisation. The amplitude and timing of these speed variations differed between glaciers, with the speed‐up being larger and more prolonged at our fastest study glacier. At all glaciers, however, the seasonal variations in ice flow are consistent with inferred changes in hydraulic efficiency of the subglacial drainage system, and qualitatively indicative of a flow regime in which annually‐averaged ice velocity is relatively insensitive to inter‐annual variations in meltwater supply – so‐called ‘ice flow self‐regulation’. These findings suggest that subglacial channel formation may exert a strong control on seasonal ice flow variations, even at fast‐flowing tidewater glaciers.Publisher PDFPeer reviewe

A model for tidewater glacier undercutting by submarine melting

Dynamic change at the marine-terminating margins of the Greenland Ice Sheet may be initiated by the ocean, particularly where subglacial runoff drives vigorous ice-marginal plumes and rapid submarine melting. Here we model submarine melt-driven undercutting of tidewater glacier termini, simulating a process which is key to understanding ice-ocean coupling. Where runoff emerges from broad subglacial channels we find that undercutting has only a weak impact on local submarine melt rate but increases total ablation by submarine melting due to the larger submerged ice surface area. Thus, the impact of melting is determined not only by the melt rate magnitude but also by the slope of the ice-ocean interface. We suggest that the most severe undercutting occurs at the maximum height in the fjord reached by the plume, likely promoting calving of ice above. It remains unclear, however, whether undercutting proceeds sufficiently rapidly to influence calving at Greenland's fastest-flowing glaciers

Broad anti-hepatitis C virus (HCV) antibody responses are associated with improved clinical disease parameters in chronic HCV infection

During hepatitis C virus (HCV) infection broadly neutralizing antibody (bNAb) responses targeting E1E2 envelope glycoproteins are generated in many individuals. It is unclear if these antibodies play a protective or a pathogenic role during chronic infection. In this study, we investigated whether bNAb responses in individuals with chronic infection were associated with differences in clinical presentation. Patient-derived purified serum IgG was used to assess the breadth of HCV E1E2 binding and neutralization activity of HCV pseudoparticles. Two panels were compared, bearing viral envelope proteins representing either an inter-genotype or an intra-genotype (gt) 1 group. We found that HCV viral load was negatively associated with strong cross-genotypic E1E2 binding (P=0.03). Overall we observed only modest correlation between total E1E2 binding and neutralizing ability. The breadth of inter-genotype neutralization did not correlate with any clinical parameters, however, analysis of individuals with gt 1 HCV infection (n=20), using an intra-genotype pseudoparticle panel, found a strong association between neutralization breadth and reduced liver fibrosis (P=0.006). Broad bNAb response in our chronic cohort was associated with a single nucleotide polymorphism (SNP) in the HLA-DQB1 gene (P=0.038) as previously reported in an acute cohort. Furthermore bNAbs in these individuals targeted more than one region of E2 neutralizing epitopes as assessed through cross-competition of patient bNAbs with well-characterized E2 antibodies. We conclude that bNAb responses in chronic gt1 infection are associated with lower rates of fibrosis and host genetics may play a role in the ability to raise such responses. IMPORTANCE: Globally there are 130-150 million people with chronic HCV infection. Typically the disease is progressive and is a major cause of severe liver cirrhosis and hepatocellular carcinoma. While it is known that neutralizing antibodies have a role in spontaneous clearance during acute infection, little is known about their role in chronic infection. In the present work we investigate the antibody response in a cohort of chronically infected individuals and find that a broad neutralizing antibody response is protective, with reduced levels of liver fibrosis and cirrhosis. We also find an association with SNPs in class II HLA genes and the presence of a broad neutralizing response indicating that antigen presentation may be important for production of HCV neutralizing antibodies

On the Ethics of Trade Credit: Understanding Good Payment Practice in the Supply Chain

In spite of its commercial importance and signs of clear concern in public policy arenas, trade credit has not been subjected to systematic, extended analysis in the business ethics literature, even where suppliers as a stakeholder group have been considered. This paper makes the case for serious consideration of the ethics of trade credit and explores the issues surrounding slow payment of debts. It discusses trade debt as a kind of promise, but— noting that not all promises are good ones—goes on to develop an analysis of the ethics of trade credit grounded in an understanding of its fundamental purpose. Making a distinction between ‘‘operating’’ trade credit and ‘‘financial’’ trade credit, the paper provides an account of the maximum period for which it is appropriate for one company to delay payment to another from which it has purchased goods or services. The concern of commentators and policy makers that companies should not take too long to pay their debts is affirmed, but the understanding of what timely payment means is significantly finessed, with one conclusion being that, if debts have not already been settled according to acceptable standard terms of trade, cash should pass quickly back along the supply chain once the customer in the final product market has paid. The analysis has implications not only for companies that take credit but also for external parties that seek to rate companies or set regulations according to speed of payment—an approach that is shown to be misleadingly simplistic, albeit well intentioned. A corresponding important responsibility for suppliers, not to extend excessive credit (and thus act as a quasi-bank), also follows from the analysis developed. Having provided a novel analysis of an important business problem, the paper then discusses some of the related practical issues and makes suggestions for further research

Effect of near-terminus subglacial hydrology on tidewater glacier submarine melt rates

Submarine melting of Greenlandic tidewater glacier termini is proposed as a possiblemechanism driving their recent thinning and retreat. We use a general circulation model, MITgcm, tosimulate water circulation driven by subglacial discharge at the terminus of an idealized tidewater glacier.We vary the spatial distribution of subglacial discharge emerging at the grounding line of the glacier andexamine the effect on submarine melt volume and distribution. We find that subglacial hydrology exerts animportant control on submarine melting; under certain conditions a distributed system can induce a factor5 more melt than a channelized system, with plumes from a single channel inducing melt over only alocalized area. Subglacial hydrology also controls the spatial distribution of melt, which has the potential tocontrol terminus morphology and calving style. Our results highlight the need to constrain near-terminussubglacial hydrology at tidewater glaciers if we are to represent ocean forcing accurately

Near-glacier surveying of a subglacial discharge plume: Implications for plume parameterizations

At tidewater glaciers, plume dynamics affect submarine melting, fjord circulation, and the mixing of meltwater. Models often rely on buoyant plume theory to parameterize plumes and submarine melting; however, these parameterizations are largely untested due to a dearth of near‐glacier measurements. Here we present a high‐resolution ocean survey by ship and remotely operated boat near the terminus of Kangerlussuup Sermia in west Greenland. These novel observations reveal the 3‐D structure and transport of a near‐surface plume, originating at a large undercut conduit in the glacier terminus, that is inconsistent with axisymmetric plume theory, the most common representation of plumes in ocean‐glacier models. Instead, the observations suggest a wider upwelling plume—a “truncated” line plume of ∼200 m width—with higher entrainment and plume‐driven melt compared to the typical axisymmetric representation. Our results highlight the importance of a subglacial outlet's geometry in controlling plume dynamics, with implications for parameterizing the exchange flow and submarine melt in glacial fjord models.NNX12AP50

Near-margin ice thickness from a portable radar: implications for subglacial water routing, Leverett Glacier, Greenland

Ice thickness measurements near the margin of the Greenland Ice Sheet (GrIS) are relatively sparse, presenting issues for modelling ice flow dynamics, ice sheet change and subglacial hydrology. We acquired ice thickness data at Leverett Glacier, western Greenland, using a highly portable, low power commercially-available ice-penetrating radar operating at 10-80 MHz. Imaging of the bed to depths of 270 m was possible using this system. Our ice thickness measurements were incorporated into the BedMachine model of bed elevation created using mass conservation methods. The new data significantly modified the modelled ice thickness and routing of subglacial water in both the Leverett and adjacent Russell Glacier. Though changes to the modelled basal topography and subglacial hydrology are consistent with observations, our new data unrealistically reduced the overall size of the Leverett hydrological catchment. Additional ice thickness measurements are therefore required to realistically constrain subglacial topography and subglacial hydrological routing in this area. Our work has significantly enhanced our understanding of basal topography and subglacial hydrology of Leverett Glacier, with implications for glacier dynamics and assessments of water piracy between catchments in the marginal zone of the GrIS

The Role of Individual Variables, Organizational Variables and Moral Intensity Dimensions in Libyan Management Accountants’ Ethical Decision Making

This study investigates the association of a broad set of variables with the ethical decision making of management accountants in Libya. Adopting a cross-sectional methodology, a questionnaire including four different ethical scenarios was used to gather data from 229 participants. For each scenario, ethical decision making was examined in terms of the recognition, judgment and intention stages of Rest’s model. A significant relationship was found between ethical recognition and ethical judgment and also between ethical judgment and ethical intention, but ethical recognition did not significantly predict ethical intention—thus providing support for Rest’s model. Organizational variables, age and educational level yielded few significant results. The lack of significance for codes of ethics might reflect their relative lack of development in Libya, in which case Libyan companies should pay attention to their content and how they are supported, especially in the light of the under-development of the accounting profession in Libya. Few significant results were also found for gender, but where they were found, males showed more ethical characteristics than females. This unusual result reinforces the dangers of gender stereotyping in business. Personal moral philosophy and moral intensity dimensions were generally found to be significant predictors of the three stages of ethical decision making studied. One implication of this is to give more attention to ethics in accounting education, making the connections between accounting practice and (in Libya) Islam. Overall, this study not only adds to the available empirical evidence on factors affecting ethical decision making, notably examining three stages of Rest’s model, but also offers rare insights into the ethical views of practising management accountants and provides a benchmark for future studies of ethical decision making in Muslim majority countries and other parts of the developing world