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Introduction
Publications
Publications (210)
Marine-terminating outlet glacier terminus traces, mapped from satellite and aerial imagery, have been used extensively in understanding how outlet glaciers adjust to climate change variability over a range of timescales. Numerous studies have digitized termini manually, but this process is labor intensive, and no consistent approach exists. A lack...
Basal properties beneath ice streams and glaciers are known to be a control for ice flow dynamics, hence knowledge of them is crucial for predicting sea level due to changes in glacial dynamics. Basal properties, processes and topography also drive the formation of subglacial landforms. Bed properties beneath Rutford Ice Stream (West Antarctica) ha...
The slip of glaciers over the underlying bed is the dominant mechanism governing the migration of ice from land into the oceans, contributing to sea-level rise. Yet glacier slip remains poorly understood or constrained by observations. Here we observe both frictional shear-stress and slip at the bed of an ice stream, using 100,000 repetitive stick-...
The number of gigaton‐sized iceberg‐calving events occurring annually at Greenland glaciers is increasing, part of a larger trend of accelerating mass loss from the Greenland Ice Sheet. Though visual observation of large calving events is rare, ∼60 glacial earthquakes generated by these calving events are currently recorded each year by regional an...
Marine-terminating outlet glacier terminus traces, mapped from satellite and aerial imagery, have been used extensively in understanding how outlet glaciers adjust to climate change variability over a range of time scales. Numerous studies have digitized termini manually, but this process is labor-intensive, and no consistent approach exists. A lac...
Almost half of the Greenland ice sheet's mass loss occurs through iceberg calving at marine terminating glaciers. The presence of buoyant subglacial discharge plumes at these marine termini are thought to increase mass loss both through submarine melting and by undercutting that consequently increases calving rates. Plume models are used to predict...
Large marine-terminating glaciers around the margins of the Greenland Ice Sheet have retreated, accelerated and thinned over the last two decades. Relatively little is known about the longer term behaviour of the Greenland Ice Sheet, yet this information is valuable for assessing the significance of modern changes. We address this by reporting 11 n...
Køge Bugt, in southeast Greenland, hosts three of the largest glaciers of the Greenland Ice Sheet; these have been major contributors to ice loss in the last two decades. Despite its importance, the Holocene history of this area has not been investigated. We present a 9100 year sediment core record of glaciological and oceanographic changes from an...
Supraglacial lake drainage events are common on the Greenland Ice Sheet. Observations on the west coast typically show an up-glacier progression of drainage as the annual melt extent spreads inland. We use a suite of remote sensing and modelling techniques in order to study a series of lakes and water-filled crevasses within 20km of the terminus of...
In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. Here, we identify a strong correspondence between mid-depth ocea...
Many researchers have analysed the effect of wind on fjord dynamics by using two-dimensional numerical models. This paper investigates the wind and tidal forcing effects on the strong stratification and circulation by application of the three-dimensional model TELEMAC-3D. The capability of the model to reproduce the physical processes has been inve...
Cross-borehole radar (XBHR) is widely used for the quantification of pore-scale liquid water in geologic materials, inferred from bulk velocity variations caused by differences in electromagnetic properties between the water and the surrounding material. The XBHR can accurately and repeatedly measure variation at depth, with sampled material remain...
Interactions between glaciers and the ocean are key for understanding the dynamics of the cryosphere in the climate system. Here we investigate the role of hydrostatic forces in glacier calving. We develop a mathematical model to account for the elastic deformation of glaciers in response to three effects: (i) marine and lake-terminating glaciers t...
Overall mass loss from the Greenland ice sheet nearly doubled during the early 2000s resulting in an increased contribution to sea-level rise, with this step-change being mainly attributed to the widespread frontal retreat and accompanying dynamic thinning of tidewater glaciers. Changes in glacier calving-front positions are easily derived from rem...
Overall mass loss from the Greenland ice sheet nearly doubled during the early 2000s resulting in an increased contribution to sea-level rise, with this step-change being mainly attributed to the widespread frontal retreat and accompanying dynamic thinning of tidewater glaciers. Changes in glacier calving-front positions are easily derived from rem...
Nearly half of Greenland's mass loss occurs through iceberg calving, but the physical mechanisms operating during calving are poorly known and in situ observations are sparse. We show that calving at Greenland's Helheim Glacier causes a minutes-long reversal of the glacier's horizontal flow and a downward deflection of its terminus. The reverse mot...
We investigate three annual mass-balance cycles on Helheim Glacier in south-east Greenland using TanDEM-X interferometric digital elevation models (DEMs), bedrock GPS measurements, and ice velocity from feature-tracking. The DEMs exhibit seasonal surface elevation cycles at elevations up to 800 m.a.s.l. with amplitudes of up to 19 m, from a maximum...
During summer 2013 we installed a network of 19 GPS nodes at the ungrounded margin of Helheim Glacier in southeast Greenland together with three cameras to study iceberg calving mechanisms. The network collected data at rates up to every 7 s and was designed to be robust to loss of nodes as the glacier calved. Data collection covered 55 days, and m...
Glaciers on the Antarctic Peninsula have recently shown changes in extent, velocity and thickness, yet there is little quantification of change in the mass balance of individual glaciers or the processes controlling changes in extent. Here a high-resolution digital elevation model and a semi-automated drainage basin delineation method have been use...
This paper provides an overview of a wide area wireless sensor network that was deployed on the calving front of the Helheim Glacier in Greenland during the summer of 2013. The purpose of the network was to measure the flow rate of the glacier using accurate satellite positioning data. The challenge in this extreme environment was to collect data i...
Recent rapid changes in the marine-terminating sectors of the Greenland Ice Sheet (GrIS) have prompted concerns about the future stability of the ice sheet. Long-term records of ice sheet behaviour provide valuable context to assess the magnitude of current change and may help resolve the mechanisms driving deglaciation. We report 23 new 10Be expos...
Iceberg calving accounts for a significant proportion of annual mass loss from marine-terminating glaciers(1,2) and may have been a factor in the rapid demise of ancient ice sheets(3). The largest contributions from the main outlet glaciers of the Greenland ice sheet to sea-level rise over the next two centuries have been projected to be dynamic in...
. Ground-penetrating radar has been widely used to map the thermal structure of polythermal glaciers. Hitherto, the cold–temperate transition surface (CTS) in radargrams has been identified by a labour-intensive and subjective manual picking method. We introduce a new automatic approach for picking the CTS that uses the difference in signal power e...
Calving is an important mass-loss process for many glaciers worldwide, and
has been assumed to respond to a variety of environmental influences. We
present a grounded, flowline tidewater glacier model using a physically-based
calving mechanism, applied to Helheim Glacier, eastern
Greenland. By qualitatively examining both modelled size and frequenc...
Acceleration of the Greenland Ice Sheet (GrIS) tidewater outlet glaciers has increased the ice sheet's contribution to global sea-level rise over the last two decades. Coincident increases in atmospheric temperatures around Greenland explain some of the increased ice loss, but warm Atlantic-origin water (AW) is increasingly recognised as contributi...
A number of problems in contemporary glaciology could benefit from the
application of adjoint models. On a simple level, adjoint models can be
used to calculate ice-sheet sensitivities with respect to spatially
varying parameters such as the basal sliding coefficient. At a more
sophisticated level, adjoint models may be used as components of
variat...
Calving is an important mass-loss process for many glaciers worldwide,
and has been assumed to respond to a variety of environmental
influences. We present a grounded, flowline tidewater glacier model,
using a physically realistic calving mechanism, which is applied to
Helheim Glacier, East Greenland. By qualitatively examining both
modelled size a...
We show that geophysical methods offer an effective means of quantifying snow thickness and density. Opportunistic (efficient but non-optimized) seismic refraction and ground-penetrating radar (GPR) surveys were performed on Storglaciären, Sweden, co-located with a snow pit that shows the snowpack to be 1.73 m thick, with density increasing from ∼1...
We have investigated the speed of compressional waves in a polythermal glacier by, first, predicting them from a simple three-phase (ice, air, water) model derived from a published ground-penetrating radar study, and then comparing them with field data from four orthogonally orientated walkaway vertical seismic profiles (VSPs) acquired in an 80 m d...
We use sequences of TanDEM-X acquisitions over 'supersites' Helheim and
Kangerdlugssuaq glaciers in south-east Greenland to generate
interferometric digital elevation models (DEMs) and to feature-track
surface displacement between image acquisitions. The high spatial
resolution, day/night, and cloud-penetrating capabilities of the X-band
SAR system...
Glaciers on the Antarctic Peninsula (AP) have recently shown changes in
extent, velocity and thickness. Understanding the response of glaciers
to warming air temperatures and ocean circulation changes in this region
is critical for understanding future mass balance changes, and yet there
is little quantification of change in the mass balance of ind...
Ground Penetrating Radar (GPR) has been widely used to derive
information on thermal properties of polythermal glaciers. The thermal
properties have far reaching ramifications on the flow behavior of
glaciers. Ice at the pressure melting point (temperate ice) which
contains inter-crystalline water exhibits much higher strain rates than
cold ice whe...
Studying the future behaviour of the Greenland Ice Sheet is important
considering the ice sheet has a sea-level equivalent of 7 metres and the
rate of mass loss from it is increasing (Velicogna, 2009). Examining the
modelled response of the Greenland Ice Sheet to changes in forcing
parameters can give insight into how it will behave in the future....
As part of a multi-disciplinary, multi-national project investigating
the ice-dynamic implications of rapidly draining supraglacial lakes on
the West Greenland Ice Sheet, we have conducted a series of seismic
reflection experiments immediately following the rapid drainage of Lake
F in the land-terminating Russell Glacier catchment to [1] isolate th...
Calving glaciers have been identified as having a crucial role in the
mass balance of the Greenland Ice Sheet, with acceleration and retreat
of these glaciers resulting in major mass loss from the ice sheet
interior, leading to a corresponding sea level rise. The ability to
reproduce observed glacier behaviour in calving models is very
desirable, b...
The behaviour of supraglacial lakes on the Greenland Ice Sheet,
specifically with regard to their drainage through hydrofracturing to
the ice sheet base, has received a great deal of recent attention.
However, a previous study has shown that this mode of drainage accounts
for only 13% of the lakes on the Greenland Ice Sheet. No published work
to da...
The behaviour of supraglacial lakes on the Greenland Ice Sheet has
attracted a great deal of focus, specifically with regard to their fast
drainage through hydrofracturing to the ice sheet base. However, a
previous study has shown that this mode of drainage accounts for only
13% of the lakes on the Greenland Ice Sheet. No published work to date
has...
A high resolution surface topography Digital Elevation Model (DEM) is
required to underpin studies of the complex glacier system on the
Antarctic Peninsula. A complete DEM with better than 200 m pixel size
and high positional and vertical accuracy would enable mapping of all
significant glacial basins and provide a dataset for glacier morphology
an...
The cryosphere, comprising snow, river and lake ice, sea ice, glaciers, ice shelves and ice sheets, and frozen ground, plays a major role in the Earth’s climate system through its impact on the surface energy budget, the water cycle, primary productivity, surface gas exchange and sea level. The cryosphere is thus a fundamental control on the physic...
A new implementation of a calving model, using the finite-element code Elmer, is presented and used to investigate the effects of surface water within crevasses on calving rate. For this work, we use a two-dimensional flowline model of Columbia Glacier, Alaska. Using the glacier's 1993 geometry as a starting point, we apply a crevasse-depth calving...
Daugaard Jensen Gletscher, Greenland, is a large tidewater glacier terminating in the northwest corner of the Scoresby Sund fjords. We present a time series of surface flow speeds spanning 1985–2010 based on feature tracking of satellite images. The time series confirms that flow speeds remained stable and reveals a persistent summer acceleration o...
Changes in the volume and extent of land ice of the Svalbard archipelago
have been the subject of considerable research since their sensitivity
to changes in climate was first noted. However, the measurement of these
changes is often necessarily based on point or profile measurements
which may not be representative if extrapolated to a whole catchm...
The Greenland ice sheet is experiencing increasing rates of mass loss,
the majority of which results from changes in discharge from tidewater
glaciers. Both atmospheric and ocean drivers have been implicated in
these dynamic changes, but understanding the nature of the response has
been hampered by the lack of measurements of glacier flow rates
pre...
Fridtjovbreen, Svalbard, is a partially tidewater-terminating glacier that started a 7-year surge during the 1990s. Flow peaked during 1996 and no surge front was apparent. We use two pre-surge (1969 and 1990) and a post-surge (2005) digital elevation models (DEMs) together with a bed DEM to quantify volume changes and iceberg calving during the su...
Seismic amplitude-versus-angle (AVA) methods are a powerful means of
quantifying the physical properties of subglacial material, but serious
interpretative errors can arise when AVA is measured over a
thinly-layered substrate. A substrate layer with a thickness less than
1/4 of the seismic wavelength, λ, is considered "thin", and
reflections from i...
The Greenland ice sheet is experiencing increasing rates of mass loss, the majority of which results from changes in discharge from tidewater glaciers. Both atmospheric and ocean drivers have been implicated in these dynamic changes but understanding the nature of the response has been hampered by the lack of measurements of glacier flow rates pred...
A high resolution surface topography Digital Elevation Model (DEM) is required to underpin studies of the complex glacier system on the Antarctic Peninsula. A complete DEM with better than 200 m pixel size and high positional and vertical accuracy would enable mapping of all significant glacial basins and provide a dataset for glacier morphology an...
Recent changes in speed, thinning, and retreat rates of marine-terminating outlet glaciers have raised concerns about the future stability of the Greenland Ice Sheet. Establishing a longer term record of outlet glacier retreat rates is essential to provide a context for present-day observations and to improve and constrain numerical models of outle...
The physical properties of subglacial material can be estimated using
seismic amplitude-versus-angle (AVA) methods, although the
interpretation of an AVA response is complicated in the case of a
thinly-layered substrate. If the thickness of a layer is less than
one-quarter of the seismic wavelength, it is considered seismically
'thin' and its upper...
Large-scale changes have been reported in many areas of the Greenland
ice sheet in the past decade and most of these changes are attributed to
dynamic mass loss of marine terminating outlet glaciers. Therefore,
iceberg calving is suspected to be one of the main contributors to
Greenland overall mass loss, but no ice sheet wide studies exist at the...
Over the past 2 decades, large outlet glaciers in western and
southeastern Greenland have accelerated, thinned, and retreated [Rignot
and Kanagaratnam, 2006; Howat et al., 2007], leading to a doubling of
Greenland's contribution to sea level rise. Scientists believe that
these changes were driven partly by increased submarine melting at the
front o...
The measured rise in eustatic sea level over the 20th century was
dominated by mass loss from the world's mountain glaciers and ice caps,
and predictions suggest that these fresh water reservoirs will remain
significant into the 21st century. However, estimates of this mass
transfer to the ocean are based on a limited number of observations
extrapo...
This paper presents the changes in the thermal structure of the polythermal glacier Storglaciären, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-pene...
The evolution of ice dynamics through surges of four tidewater-terminating glaciers in northwest Svalbard is investigated by remote sensing. A 20 year time series of glacier surface flow speeds and frontal positions is presented covering the recent surges of Monacobreen, Comfortlessbreen, Blomstrandbreen and Fjortende Julibreen. Surface flow speeds...
Seismic amplitude-versus-angle (AVA) methods are a powerful means of interpreting the physical properties of subglacial material, although interpreting an AVA response is complicated in the case of a thinly-layered substrate. A layer thinner than one-quarter of the seismic wavelength is considered seismically "thin", and reflections from its boundi...