Brief Communication: Further summer speedup of Jakobshavn Isbræ

We have extended the record of flow speed on Jakobshavn Isbræ through the summer of 2013. These new data reveal large seasonal speedups, 30 to 50% greater than previous summers. At a point a few kilometres inland from the terminus, the mean annual speed for 2012 is nearly three times as great as that in the mid-1990s, while the peak summer speeds are more than a factor of four greater. These speeds were achieved as the glacier terminus appears to have retreated to the bottom of an over-deepened basin with a depth of ~ 1300 m below sea level. The terminus is likely to reach the deepest section of the trough within a few decades, after which it could rapidly retreat to the shallower regions ~ 50 km farther upstream, potentially by the end of this century

A secondary sisterhood: Revisioning nineteenth-century homosocial bonds between women

Images from http://www.manfeels-park.com/comic/lake-scene/ reproduced with permissionThis dissertation explores the ways in which revisionary fiction engages with understanding that nineteenth-century gender constructs negatively impacted women’s homosocial bonds. It examines three different periods throughout the nineteenth-century to reflect upon the ways in which revisionary texts engage with changing cultural ideologies throughout the period. Beginning with Austen’s Pride and Prejudice (1813), and comparing this to the text and television adaptation Death Comes to Pemberley (2011, 2013), Chapter one examines the ways in which James’s text interprets Austen’s potentially proto-feminist comment on female homosocialism. It draws upon the ways in which the ‘Jane Austen’ brand has potentially influenced James’s text, but also reflects on how the brand continues to move with changing modern cultures through recent representations such as the internet comic, Manfeels Park. Chapter two takes a leap forward into the mid- to late-Victorian period and explores the ways in which lesbian potential may have also been affected by the secondary conditions of women’s homosocial bonds. It examines how Sarah Waters’ neo-Victorian texts Fingersmith and Tipping the Velvet write over the dearth of lesbian representation in canonical literature of the period. Chapter three examines representation of the New Woman in The Odd Women (1893), the film, Hysteria (2011) and The Crimson Petal and the White (2002). It compares the ways in which her attempt to carve out a new kind of female homosocialism has a unique link to the present because of the New Woman’s ‘modern’ approach. It examines the representation of her as an individual in revisionary texts, compared to her as part of a collective in The Odd Women, and how this makes suggestions about the state of modern feminism

Reframing assessment research: through a practice perspective

Assessment as a field of investigation has been influenced by a limited number of perspectives. These have focused assessment research in particular ways that have emphasised measurement, or student learning or institutional policies. The aim of this paper is to view the phenomenon of assessment from a practice perspective drawing upon ideas from practice theory. Such a view places assessment practices as central. This perspective is illustrated using data from an empirical study of assessment decision-making and uses as an exemplar the identified practice of ‘bringing a new assessment task into being’. It is suggested that a practice perspective can position assessment as integral to curriculum practices and end separations of assessment from teaching and learning. It enables research on assessment to de-centre measurement and take account of the wider range of people, phenomena and things that constitute it

How university teachers design assessments: a cross disciplinary study

There are dissonances between educators’ aspirations for assessment design and actual assessment implementation in higher education. Understanding how assessment is designed ‘on the ground’ can assist in resolving this tension. Thirty-three Australian university educators from a mix of disciplines and institutions were interviewed. A thematic analysis of the transcripts indicated that assessment design begins as a response to an impetus for change. The design process itself was shaped by environmental influences, which are the circumstances surrounding the assessment design, and professional influences, which are those factors that the educators themselves bring to the process. A range of activities or tasks were undertaken, including those which were essential to all assessment design, those more selective activities which educators chose to optimise the assessment process in particular ways and meta-design processes which educators used to dynamically respond to environmental influences. The qualitative description indicates the complex social nature of interwoven personal and environmental influences on assessment design and the value of an explicit and strategic ways of thinking within the constraints and affordances of a local environment. This suggests that focussing on relational forms of professional development that develops strategic approaches to assessment may be beneficial. The role of disciplinary approaches may be significant and remains an area for future research

Ice velocity of Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm, 2015–2017, from Sentinel 1-a/b SAR imagery

Systematically monitoring Greenland's outlet glaciers is central to understanding the timescales over which their flow and sea level contributions evolve. In this study we use data from the new Sentinel-1a/b satellite constellation to generate 187 velocity maps, covering four key outlet glaciers in Greenland: Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm. These data provide a new high temporal resolution record (6-day averaged solutions) of each glacier's evolution since 2014, and resolve recent seasonal speedup periods and inter-annual changes in Greenland outlet glacier speed with an estimated certainty of 10 %. We find that since 2012, Jakobshavn Isbræ has been decelerating, and now flows approximately 1250 m yr−1 (10 %), slower than 5 years previously, thus reversing an increasing trend in ice velocity that has persisted during the last decade. Despite this, we show that seasonal variability in ice velocity remains significant: up to 750 m yr−1 (14 %) at a distance of 12 km inland of the terminus. We also use our new dataset to estimate the duration of speedup periods (80–95 days) and to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbræ, with increases in speed of  ∼  1800 m yr−1 in response to 1 km of retreat. Elsewhere, we record significant seasonal changes in flow of up to 25 % (2015) and 18 % (2016) at Petermann Glacier and Zachariæ Isstrøm, respectively. This study provides a first demonstration of the capacity of a new era of operational radar satellites to provide frequent and timely monitoring of ice sheet flow, and to better resolve the timescales over which glacier dynamics evolve

High-resolution ice-thickness mapping in South Greenland

Airborne radar sounding is difficult in South Greenland because of the presence of englacial water, which prevents the signal from reaching the bed. Data coverage remains suboptimal for traditional methods of ice-thickness and bed mapping that rely on geostatistical techniques, such as kriging, because important features are missing. Here we apply two alternative approaches of highresolution (̃300 m) ice-thickness mapping, that are based on the conservation of mass, to two regions of South Greenland: (1) Qooqqup Sermia and Kiattuut Sermiat, and (2) Ikertivaq. These two algorithms solve optimization problems, for which the conservation of mass is either enforced as a hard constraint, or as a soft constraint. For the first region, very few measurements are available but there is no gap in ice motion data, whereas for Ikertivaq, more ice-thickness measurements are available, but there are gaps in ice motion data. We show that mass-conservation algorithms can be used as validation tools for radar sounding. We also show that it is preferable to apply mass conservation as a hard constraint, rather than a soft constraint, as it better preserves elongated features, such as glacial valleys and ridges

Increased ice flow in Western Palmer Land linked to ocean melting

A decrease in the mass and volume of Western Palmer Land has raised the prospect that ice speed has increased in this marine-based sector of Antarctica. To assess this possibility, we measure ice velocity over 25 years using satellite imagery and an optimized modeling approach. More than 30 unnamed outlet glaciers drain the 800 km coastline of Western Palmer Land at speeds ranging from 0.5 to 2.5 m/d, interspersed with near-stagnant ice. Between 1992 and 2015, most of the outlet glaciers sped up by 0.2 to 0.3 m/d, leading to a 13% increase in ice flow and a 15 km3/yr increase in ice discharge across the sector as a whole. Speedup is greatest where glaciers are grounded more than 300 m below sea level, consistent with a loss of buttressing caused by ice shelf thinning in a region of shoaling warm circumpolar water

Greenland Ice Mapping Project: ice flow velocity variation at sub-monthly to decadal timescales

We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbræ began slowing substantially in 2017, with a midsummer peak that was even slower than some previous winter minima. Over the last decade, we identify two major slowdown events at Køge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in north-west and south-west Greenland to produce a record of speed-up since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speed-up. In addition, we computed trends in winter flow speed for much of the south-west margin of the ice sheet and find little in the way of statistically significant changes over the period covered by our data. Finally, although the consistency of the data is generally good over time and across sensors, our analysis indicates that substantial differences can arise in regions with high strain rates (e.g. shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.</p

Subglacial sediments: A regional geological template for ice flow in West Antarctica

We use aerogeophysical data to estimate the distribution of marine subglacial sediments and fault“bounded sedimentary basins beneath the West Antarctic Ice Sheet (WAIS). We find that significant ice flow occurs exclusively in regions covered by subglacial sediments. The onsets and lateral margins of ice streams coincide with the limit of marine sediments. Lateral margins are also consistently linked with fault“bounded basins. We predict that the inland migration of ice streams B and C 1 towards the ice divide outside the region covered by marine or rift sediments is unlikely. The subglacial geology has the potential to modulate the dynamic evolution of the ice streams and the WAIS