Delicate seafloor landforms reveal past Antarctic grounding-line retreat of kilometers per year.

A suite of grounding-line landforms on the Antarctic seafloor, imaged at submeter horizontal resolution from an autonomous underwater vehicle, enables calculation of ice sheet retreat rates from a complex of grounding-zone wedges on the Larsen continental shelf, western Weddell Sea. The landforms are delicate sets of up to 90 ridges, 10 kilometers per year) are inferred during regional deglaciation of the Larsen shelf. If repeated today, such rapid mass loss to the ocean would have clear implications for increasing the rate of global sea level rise

Поверхностные скорости и айсберговый сток ледникового купола Академии Наук на Северной Земле

We have determined the ice-surface velocities of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, during the period November 2016 – November 2017, using intensity offset-tracking of Sentinel-1 synthetic-aperture radar images. We used the average of 54 pairs of weekly velocities (with both images in each pair separated by a12-day period) to estimate the mean annual ice discharge from the ice cap. We got an average ice discharge for 2016–2017 of 1,93±0,12 Gt a−1, which is equivalent to −0,35±0,02 m w.e. a−1 over the whole area of the ice cap. The difference from an estimate of ~1,4 Gt a−1 for 2003–2009 can be attributed to the initiation of ice-stream flow in Basin BC sometime between 2002 and 2016. Since the front position changes between both periods have been negligible, ice discharge is equivalent to calving flux. We compare our results for calving flux with those of previous studies and analyse the possible drivers of the changes observed along the last three decades. Since these changes do not appear to have responded to environmental changes, we conclude that the observed changes are likely driven by the intrinsic characteristics of the ice cap governing tidewater glacier dynamics.По 54 парам космических снимков Sentinel‐1, сделанных с ноября 2016 г. по ноябрь 2017 г., определены скорости движения ледникового купола Академии Наук на Северной Земле. На этой основе оценён среднегодовой расход льда в море этого купола (1,93±0,12 Гт/год), установлены основные пути стока льда, проведено сравнение с прежними оценками

Large-scale sedimentation on the glacier-influenced polar North Atlantic Margins: Long-range side-scan sonar evidence

Long-range side-scan sonar (GLORIA) imagery of over 600,000 km² of the Polar North Atlantic provides a large-scale view of sedimentation patterns on this glacier-influenced continental margin. High-latitude margins are influenced strongly by glacial history and ice dynamics and, linked to this, the rate of sediment supply. Extensive glacial fans (up to 350,000 km³) were built up from stacked series of large debris flows transferring sediment down the continental slope. The fans were linked with high debris inputs from Quaternary glaciers at the mouths of cross-shelf troughs and deep fjords. Where ice was slower-moving, but still extended to the shelf break, large-scale slide deposits are observed. Where ice failed to cross the continental shelf during full glacials, the continental slope was sediment starved and submarine channels and smaller slides developed. A simple model for large-scale sedimentation on the glaciated continental margins of the Polar North Atlantic is presented

Scott Polar Research Institute Arctic Airborne Radio-Echo Sounding Datasets: Canadian Arctic 2000

This data set contains radar sounder profiles from the SPRI 100 MHz ice-penetrating radar instrument over Devon and Ellesmere islands in the Canadian Arctic (CA). Along with the radar profile data, the archive includes derived and ancillary data, plus software code produced for acquisition and working up of data. The data were collected under funding from a UK Natural Environment Research Council (NERC) grant (GR3/12469) to Prof. J. A. Dowdeswell. Please consult the 'MetadataCA2000.pdf' file for a detailed description of the dataset and its contents.Funding: The collection of these data was funded by NERC grant GR3/12469 to J.A. Dowdeswell, as well as by grants from the Meteorological Service of Canada (CRYSYS program) to M.J. Sharp. Further funding (to J.A. Dowdeswell) for development of the dataset was provided by the NERC Centre for Polar Observation and Modelling, UK, and the EU SPICE Project

A tidewater glacier landform assemblage in Belcher Inlet, Canadian Arctic

Belcher Glacier, a 35 km-long tidewater outlet glacier of the 12,000 km² ice cap on Devon Island (Dowdeswell et al. 2004), is one of the fastest-flowing glaciers in the Canadian Arctic (Van Wychen et al. 2014) (Fig. 1). Belcher Glacier and neighbouring Fitzroy Glacier to the southeast account for about 55% of the iceberg calving loss from the Devon Ice Cap (Van Wychen et al. 2014). The terminus of Belcher Glacier remained relatively stable between the 1960s (light blue dashed line in Fig. 1a) and 2000 (Landsat 7 satellite image in Fig. 1a). In contrast, the unnamed glacier immediately to the north retreated 2 km during this period (Fig. 1a). Belcher Glacier and the unnamed glacier retreated around 500 m and 250 m, respectively, between 2000 and 2014 (dark blue dashed line in Fig. 1a). The bed topography of Belcher Glacier, which is around 250 m below sea level at the present-day glacier margin (Fig. 1c) and remains below sea level in the lower 11 km of the glacier, suggests that its terminus region may become unstable in the event of future retreat. Seafloor mapping of Belcher Inlet beyond the termini of Belcher Glacier and the unnamed glacier (Fig. 1a), together with sub-bottom profiling, provide information about the dynamic behaviour of tidewater glaciers.This is the author accepted manuscript. The final version is available from Geological Society of London via https://doi.org/10.1144/M46.14

EB Ford revisited: assessing the long-term stability of wing-spot patterns and population genetic structure of the meadow brown butterfly on the Isles of Scilly

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Data files of wing spot sizes and AFLP genotypes available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.j7v42.Understanding selection in the wild remains a major aim of evolutionary ecology and work by Ford and colleagues on the meadow brown butterfly Maniola jurtina did much to ignite this agenda. A great deal of their work was conducted during the 1950s on the Isles of Scilly. They documented island-specific wing-spot patterns that remained consistent over about a decade, but patterns on some islands changed after environmental perturbation. It was suggested that these wing-spot patterns reflected island-specific selection and that there was little migration between islands. However, genetic studies to test the underlying assumption of restricted migration are lacking and it is also unknown whether the originally described wing-spot patterns have persisted over time. We therefore collected female butterflies from five of Ford's original study locations, including three large islands (St Mary's, St Martin's and Tresco) and two small islands (Tean and St Helen's). Wing-spot patterns had not changed appreciably over time on three of the islands (two large and one small), but were significantly different on the other two. Furthermore, analysis of 176 amplified fragment length polymorphisms revealed significant genome-wide differentiation among the five islands. Our findings are consistent with Ford's conclusions that despite the close proximity of these islands, there is restricted gene flow among them.Heredity advance online publication, 2 November 2016; doi:10.1038/hdy.2016.94.We thank the Genetics Society for a fieldwork grant (to DJH) that funded the collection trip and DJH thanks Mike Johnson for sparking interest in this area. SWB is supported by the Australian Research Council and a Ramsay Fellowship, NW by a Royal Society Wolfson Fellowship and NERC and DJH by the Leverhulme Trust

Glacier velocities and dynamic ice discharge from the Queen Elizabeth Islands, Nunavut, Canada

Recent studies indicate an increase in glacier mass loss from the Canadian Arctic Archipelago as a result of warmer summer air temperatures. However, no complete assessment of dynamic ice discharge from this region exists. We present the first complete surface velocity mapping of all ice masses in the Queen Elizabeth Islands and show that these ice masses discharged ~2.6 ± 0.8 Gt a−1 of ice to the oceans in winter 2012. Approximately 50% of the dynamic discharge was channeled through non surge-type Trinity and Wykeham Glaciers alone. Dynamic discharge of the surge-type Mittie Glacier varied from 0.90 ± 0.09 Gt a−1 during its 2003 surge to 0.02 ± 0.02 Gt a−1 during quiescence in 2012, highlighting the importance of surge-type glaciers for interannual variability in regional mass loss. Queen Elizabeth Islands glaciers currently account for ~7.5% of reported dynamic discharge from Arctic ice masses outside Greenland.We thank NSERC, Canada Foundation for Innovation, Ontario Research Fund, ArcticNet, Ontario Graduate Scholarship, University of Ottawa and the NSERC Canada Graduate Scholarship for funding. RADARSAT-2 data were provided by MacDonald, Dettwiler and Associates under the RADARSAT-2 Government Data Allocation administrated by the Canadian Space Agency. Support to DB is provided through the Climate Change Geosciences Program, Earth Sciences Sector, Natural Resources Canada (ESS Contribution #20130293). We also acknowledge support from U.K NERC for grants R3/12469 and NE/K004999 to JAD.This is the accepted version of an article published in Geophysical Research Letters. An edited version of this paper was published by AGU. Copyright (2014) American Geophysical Union. The final version is available at http://onlinelibrary.wiley.com/doi/10.1002/2013GL058558/abstract;jsessionid=6A3AD907C4383DA5D4E20C4924D6EC18.f02t02

Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode

Abstract: The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming

Icebergs in the North Atlantic: Modelling circulation changes and glacio-marine deposition

In order to investigate meltwater events in the North Atlantic, a simple iceberg generation, drift, and melting routine was implemented in a high-resolution OGCM. Starting from the modelled last glacial state, every 25th day cylindrical model icebergs 300 meters high were released at 32 specific points along the coasts. Icebergs launched at the Barents Shelf margin spread a light meltwater lid over the Norwegian and Greenland Seas, shutting down the deep convection and the anti-clockwise circulation in this area. Due to the constraining ocean circulation, the icebergs produce a tongue of relatively cold and fresh water extending eastward from Hudson Strait that must develop at this location, regardless of iceberg origin. From the total amount of freshwater inferred by the icebergs, the thickness of the deposited IRD could be calculated in dependance of iceberg sediment concentration. In this way, typical extent and thickness of Heinrich layers could be reproduced, running the model for 250 years of steady state with constant iceberg meltwater inflow