Surges of Harald Moltke Bræ, north-western Greenland: seasonal modulation and initiation at the terminus

Abstract. Harald Moltke Bræ, a marine-terminating glacier in north-western Greenland, shows episodic surges. A recent surge from 2013 to 2019 lasted significantly longer (6 years) than previously observed surges (2–4 years) and exhibits a pronounced seasonality with flow velocities varying by 1 order of magnitude (between about 0.5 and 10 m d−1) in the course of a year. During this 6-year period, the seasonal velocity always peaked in the early melt season and decreased abruptly when meltwater runoff was maximum. Our data suggest that the seasonality has been similar during previous surges. Furthermore, the analysis of satellite images and digital elevation models shows that the surge from 2013 to 2019 was preceded by a rapid frontal retreat and a pronounced thinning at the glacier front (30 m within 3 years). We discuss possible causal mechanisms of the seasonally modulated surge behaviour by examining various system-inherent factors (e.g. glacier geometry) and external factors (e.g. surface mass balance). The seasonality may be caused by a transition of an inefficient subglacial system to an efficient one, as known for many glaciers in Greenland. The patterns of flow velocity and ice thickness variations indicate that the surges are initiated at the terminus and develop through an up-glacier propagation of ice flow acceleration. Possibly, this is facilitated by a simultaneous up-glacier spreading of surface crevasses and weakening of subglacial till. Once a large part of the ablation zone has accelerated, conditions may favour substantial seasonal flow acceleration through seasonally changing meltwater availability. Thus, the seasonal amplitude remains high for 2 or more years until the fast ice flow has flattened the ice surface and the glacier stabilizes again.

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Surges of Harald Moltke Bræ, north-west Greenland: Seasonal modulation and initiation at the terminus

10.5194/tc-2020-256 ◽

2020 ◽

Author(s):

Lukas Müller ◽

Martin Horwath ◽

Mirko Scheinert ◽

Christoph Mayer ◽

Benjamin Ebermann ◽

...

Keyword(s):

Ice Flow ◽

Surface Mass ◽

West Greenland ◽

North West ◽

Flow Acceleration ◽

Ice Surface ◽

Meltwater Runoff ◽

Seasonal Flow ◽

Order Of Magnitude ◽

Thickness Variations

Abstract. Harald Moltke Bræ, a marine-terminating glacier in north-west Greenland, shows episodic surges. A recent surge from 2013 to 2019 lasted significantly longer (6 years) than previously observed surges (2–4 years) and exhibits a pronounced seasonality with flow velocities varying by one order of magnitude (between about 0.5 and 10 m/day) in the course of a year. During this six-year period, the velocity always peaked in the early melt season and decreased abruptly when meltwater runoff was maximum. Our data suggest that the seasonality has been similar during previous surges, and, to a much lesser extent, during the intermediate quiescent phases. It is peculiar to Harald Moltke Bræ that the seasonal amplitude is amplified episodically to constitute glacier surges. The surge from 2013 to 2019 was preceded by a rapid frontal retreat and a pronounced thinning at the glacier front (30 m within 3 years). We discuss possible causal mechanisms of the seasonally modulated surge behaviour by involving various system inherent factors (e.g. glacier geometry) and external factors (e.g. surface mass balance). The seasonality may be caused by a transition of an inefficient subglacial system to an efficient one, as known for many glaciers in Greenland. The patterns of flow velocity and ice thickness variations indicate that the surges are initiated at the terminus and develop through an up-glacier propagation of ice flow acceleration. Possibly, this is facilitated by a simultaneous up-glacier spreading of surface crevasses and weakening of subglacial till. Once a large part of the ablation zone has accelerated, conditions may favour substantial seasonal flow acceleration through seasonally changing meltwater availability. Thus the seasonal amplitude remains high for two or more years until the fast ice flow has flattened the ice surface and the glacier stabilizes again.

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A system of conservative regridding for ice–atmosphere coupling in a General Circulation Model (GCM)

Geoscientific Model Development ◽

10.5194/gmd-7-883-2014 ◽

2014 ◽

Vol 7 (3) ◽

pp. 883-907 ◽

Cited By ~ 10

Author(s):

R. Fischer ◽

S. Nowicki ◽

M. Kelley ◽

G. A. Schmidt

Keyword(s):

General Circulation Model ◽

General Circulation ◽

Circulation Model ◽

Grid Cell ◽

Surface Model ◽

Ice Flow ◽

Surface Mass ◽

Flow Models ◽

Ice Surface ◽

Ice Model

Abstract. The method of elevation classes, in which the ice surface model is run at multiple elevations within each grid cell, has proven to be a useful way for a low-resolution atmosphere inside a general circulation model (GCM) to produce high-resolution downscaled surface mass balance fields for use in one-way studies coupling atmospheres and ice flow models. Past uses of elevation classes have failed to conserve mass and energy because the transformation used to regrid to the atmosphere was inconsistent with the transformation used to downscale to the ice model. This would cause problems for two-way coupling. A strategy that resolves this conservation issue has been designed and is presented here. The approach identifies three grids between which data must be regridded and five transformations between those grids required by a typical coupled atmosphere–ice flow model. This paper develops a theoretical framework for the problem and shows how each of these transformations may be achieved in a consistent, conservative manner. These transformations are implemented in Glint2, a library used to couple atmosphere models with ice models. Source code and documentation are available for download. Confounding real-world issues are discussed, including the use of projections for ice modeling, how to handle dynamically changing ice geometry, and modifications required for finite element ice models.

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Winter drainage of surface lakes on the Greenland Ice Sheet from Sentinel-1 SAR imagery

The Cryosphere ◽

10.5194/tc-15-1587-2021 ◽

2021 ◽

Vol 15 (3) ◽

pp. 1587-1606

Author(s):

Corinne L. Benedek ◽

Ian C. Willis

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Shape From Shading ◽

Lake Area ◽

Ice Flow ◽

Surface Mass ◽

Flow Acceleration ◽

Optical Imagery ◽

Sar Imagery ◽

Lake Drainage

Abstract. Surface lakes on the Greenland Ice Sheet play a key role in its surface mass balance, hydrology and biogeochemistry. They often drain rapidly in the summer via hydrofracture, which delivers lake water to the ice sheet base over timescales of hours to days and then can allow meltwater to reach the base for the rest of the summer. Rapid lake drainage, therefore, influences subglacial drainage evolution; water pressures; ice flow; biogeochemical activity; and ultimately the delivery of water, sediments and nutrients to the ocean. It has generally been assumed that rapid lake drainage events are confined to the summer, as this is typically when observations are made using satellite optical imagery. Here we develop a method to quantify backscatter changes in satellite radar imagery, which we use to document the drainage of six different lakes during three winters (2014/15, 2015/16 and 2016/17) in fast-flowing parts of the Greenland Ice Sheet. Analysis of optical imagery from before and after the three winters supports the radar-based evidence for winter lake drainage events and also provides estimates of lake drainage volumes, which range between 0.000046 ± 0.000017 and 0.0200 ± 0.002817 km3. For three of the events, optical imagery allows repeat photoclinometry (shape from shading) calculations to be made showing mean vertical collapse of the lake surfaces ranging between 1.21 ± 1.61 and 7.25 ± 1.61 m and drainage volumes of 0.002 ± 0.002968 to 0.044 ± 0.009858 km3. For one of these three, time-stamped ArcticDEM strips allow for DEM differencing, which demonstrates a mean collapse depth of 2.17 ± 0.28 m across the lake area. The findings show that lake drainage can occur in the winter in the absence of active surface melt and notable ice flow acceleration, which may have important implications for subglacial hydrology and biogeochemical processes.

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Ice flow variations at Polar Record Glacier, East Antarctica

Journal of Glaciology ◽

10.1017/jog.2019.6 ◽

2019 ◽

Vol 65 (250) ◽

pp. 279-287 ◽

Cited By ~ 5

Author(s):

QI LIANG ◽

CHUNXIA ZHOU ◽

IAN M. HOWAT ◽

SEONGSU JEONG ◽

RUIXI LIU ◽

...

Keyword(s):

Seasonal Variations ◽

Back Stress ◽

East Antarctica ◽

Austral Spring ◽

Ice Flow ◽

Ice Shelves ◽

Flow Acceleration ◽

Ice Surface ◽

Flow Speeds ◽

Interannual Fluctuations

ABSTRACTRelatively little is known about the physical mechanisms that drive the dynamics of the East Antarctic outlet glaciers. Here we conduct a remote-sensing investigation of the Polar Record Glacier (PRG), East Antarctica to analyze its ice flow acceleration, ice front variations and ice surface melting. Ice flow speeds at PRG increased by up to 15% from 2005 to 2015, with substantial interannual fluctuations. The ice velocities also showed seasonal variations, accelerating by up to 9% between September and January. Multiple mechanisms contribute to the observed seasonal variations: the initial acceleration may result from the lost back-stress provided by the sea ice in the austral spring and the later speedup relate to the surface meltwater that leads to weakened ice shelf and shear margins. The sensitivity of the PRG to oceanic forcing is confirmed by comparing the secular ice velocity increases with ocean temperatures. These measurements suggest that the dynamics of East Antarctic ice shelves are sensitive to melt at both the surface and base, at a range of timescales.

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Inverse solution of surface mass balance of Midtre Lovénbreen, Svalbard

Journal of Glaciology ◽

10.1017/jog.2017.26 ◽

2017 ◽

Vol 63 (240) ◽

pp. 593-602 ◽

Cited By ~ 2

Author(s):

ILONA VÄLISUO ◽

THOMAS ZWINGER ◽

JACK KOHLER

Keyword(s):

Mass Balance ◽

Field Measurements ◽

Surface Mass Balance ◽

Glacier Surface ◽

Ice Flow ◽

Surface Mass ◽

Time Period ◽

Digital Elevation ◽

Extended Time Period ◽

Compute Velocity

ABSTRACTWe investigate the temporal evolution and spatial distribution of mass balance on the glacier Midtre Lovénbreen, Svalbard. Running a diagnostic high-resolution full-stress ice flow model with geometries obtained from five digital elevation models (DEMs) in the period 1962–2005, we compute velocity fields and linearly interpolated volume change of the glacier. We evaluate the kinematic free surface equation using these model outputs to solve the surface mass balance (SMB). Monitoring data on Midtre Lovénbreen allows model results to be compared with point measurements from the glacier over several decades. This method allows us to estimate the mass balance over the entire glacier surface, beyond the spatially limited field measurements, and to derive past SMB over an extended time period.

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Simulating ice thickness and velocity evolution of Upernavik Isstrøm 1849–2012 by forcing prescribed terminus positions in ISSM

10.5194/tc-2017-121 ◽

2017 ◽

Cited By ~ 1

Author(s):

Konstanze Haubner ◽

Jason E. Box ◽

Nicole J. Schlegel ◽

Eric Y. Larour ◽

Mathieu Morlighem ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Surface Elevation ◽

Surface Mass Balance ◽

Ice Flow ◽

Surface Mass ◽

Flow Acceleration ◽

Glacier Terminus ◽

Negative Surface ◽

Glacier Velocity

Abstract. Tidewater glacier velocity and mass balance are sensitive to terminus retreat. Yet, it remains challenging for ice flow models to reproduce observed ice marginal changes. Here, we simulate the 1849–2012 ice velocity and thickness changes on Upernavik Isstrøm using the Ice Sheet System Model (ISSM; Larour et al., 2012), by prescribing observed glacier terminus changes. We find that a realistic ISSM simulation of the past mass balance and velocity evolution of Upernavik Isstrøm is highly dependent on terminus retreat. At the end of the 164 year simulation, the 1990–2012 ice surface elevation and velocities and are within &pm;20 % of the observations. Thus, our model setup provides a realistic simulation of the 1849–2012 evolution for Upernavik Isstrøm. Increased ice flow acceleration is simulated during the 1930s, late 1970s and between 1995 and 2012, coinciding with increased prescribed negative surface mass balance anomalies and terminus retreat. The simulation suggests three distinct periods of mass change: (1849–1932) having near zero mass balance, (1932–1992) with ice mass loss dominated by ice dynamical flow, and (1998–2012), where increased retreat and negative surface mass balance anomalies lead to mass loss twice that of any earlier year. The main products resulting from this study are 1849–2012 reconstruction of surface elevation, velocity and grounding line position of Upernavik Isstrøm.

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Hourly surface meltwater routing for a Greenlandic supraglacial catchment across hillslopes and through a dense topological channel network

10.5194/tc-2020-273 ◽

2020 ◽

Author(s):

Colin J. Gleason ◽

Kang Yang ◽

Dongmei Feng ◽

Laurence C. Smith ◽

Kai Liu ◽

...

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Complex Surface ◽

Calibration Model ◽

Channel Measurements ◽

Channel Network ◽

Surface Mass ◽

Ice Surface ◽

Meltwater Runoff

Abstract. Recent work has identified complex perennial supraglacial stream/river networks in areas of the Greenland Ice Sheet (GrIS) ablation zone. Current surface mass balance (SMB) models appear to overestimate meltwater runoff in these networks compared to in-channel measurements of supraglacial discharge. Here, we constrain SMB models using the Hillslope River Routing Model (HRR), a spatially explicit flow routing model used in terrestrial hydrology, in a 63 km2 supraglacial river catchment in southwest Greenland. HRR conserves water mass and momentum and explicitly accounts for hillslope routing, and we produce hourly flows for nearly 10,000 channels given inputs of an ice surface DEM, a remotely sensed supraglacial channel network, SMB-modelled runoff, and an in situ discharge dataset used for calibration. Model calibration yields a Nash Sutcliffe Efficiency as high as 0.92 and physically realistic parameters. We confirm earlier assertions that SMB runoff exceeds the conserved mass of water routed to match measured flows in this catchment (by 12–59 %) and that large channels do not dewater overnight despite a diurnal shutdown of SMB runoff production. We further test hillslope routing and network density controls on channel discharge and conclude that explicitly including hillslope flow and routing runoff through a realistically fine channel network produces the most accurate results. Modelling complex surface water processes is thus both possible and necessary to accurately simulate the timing and magnitude of supraglacial channel flows, and we highlight a need for additional in situ discharge datasets to better calibrate and apply this method elsewhere on the ice sheet.

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Oceanic mechanical forcing of a marine-terminating Greenland glacier

Annals of Glaciology ◽

10.3189/2012aog60a083 ◽

2012 ◽

Vol 53 (60) ◽

pp. 181-192 ◽

Cited By ~ 53

Author(s):

Jacob I. Walter ◽

Jason E. Box ◽

Slawek Tulaczyk ◽

Emily E. Brodsky ◽

Ian M. Howat ◽

...

Keyword(s):

Tide Gauge ◽

Greenland Ice Sheet ◽

Time Lapse ◽

Flow Speed ◽

Ice Flow ◽

Flow Acceleration ◽

Order Of Magnitude ◽

Seismic Records ◽

Oceanic Forcing ◽

Continuous Gps

AbstractDynamics of marine-terminating major outlet glaciers are of high interest because of their potential for drawing down large areas of the Greenland ice sheet. We quantify short-term changes in ice flow speed and calving at a major West Greenland glacier and examine their relationship to the presence of the sea-ice melange and tidal stage. A field campaign at the terminus of Store Gletscher (70.40˚N, 50.55˚W) spanning the spring and summer of 2008 included four broadband seismometers, three time-lapse cameras, a tide gauge, an automatic weather station and an on-ice continuous GPS station. Sub-daily fluctuations in speed coincide with two modes of oceanic forcing: (1) the removal of the ice melange from the terminus front and (2) tidal fluctuations contributing to speed increases following ice melange removal. Tidal fluctuations in ice flow speed were observed 16km from the terminus and possibly extend further. Seismic records suggest that periods of intensive calving activity coincide with ice-flow acceleration following breakup of the melange in spring. A synchronous increase in speed at the front and clearing of the melange suggests that the melange directly resists ice flow. We estimate a buttressing stress (~30–60 kPa) due to the presence of the ice melange that is greater than expected from the range of observed tides, though an order of magnitude less than the driving stress.

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A high-frequency and high-resolution image time series of the Gornergletscher – Swiss Alps – derived from repeated UAV surveys

10.5194/essd-2018-145 ◽

2018 ◽

Cited By ~ 1

Author(s):

Lionel Benoit ◽

Aurelie Gourdon ◽

Raphaël Vallat ◽

Inigo Irarrazaval ◽

Mathieu Gravey ◽

...

Keyword(s):

Feature Detection ◽

Detection Algorithm ◽

Swiss Alps ◽

Glacier Surface ◽

Ice Flow ◽

Ice Surface ◽

Surface Displacements ◽

Drainage Networks ◽

Digital Elevation ◽

Very High Spatial Resolution

Abstract. The rapid growth of drone technology provides an efficient means to monitor the response of alpine glaciers to climate warming. Here we report a new dataset based on images collected during ten intensive UAV surveys of the Gornergletscher glacial system (Switzerland) carried out approximately every two weeks throughout the summer 2017. The final products, available at: https://doi.org/10.5281/zenodo.1487862 (Benoit et al, 2018), consist in a series of 10 cm resolution ortho-images, Digital Elevation Models of the glacier surface, and Matching Maps that can be used to quantify ice surface displacements and velocities. Used on its own, this dataset allows mapping the glacier and monitoring surface velocities over the summer at a very high spatial resolution. Coupled with a classification or feature detection algorithm, it enables extracting structures such as surface drainage networks, debris or snow cover. The approach we present can be used in the future to gain insights into ice flow dynamics.

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Dynamics of the Scharffenbergbotnen blue-ice area, Dronning Maud Land, Antarctica

Annals of Glaciology ◽

10.3189/172756404781814177 ◽

2004 ◽

Vol 39 ◽

pp. 417-422 ◽

Cited By ~ 9

Author(s):

Anna Sinisalo ◽

Aslak Grinsted ◽

John Moore

Keyword(s):

Mass Balance ◽

Geometrical Model ◽

Surface Velocity ◽

Geometrical Analysis ◽

Ice Flow ◽

Surface Mass ◽

Ice Surface ◽

Dronning Maud Land ◽

Dip Angle ◽

Ground Penetrating

AbstractGround-penetrating radar (GPR) surveys in Scharffenbergbotnen valley, Dronning Maud Land, Antarctica, complement earlier, relatively sparse data on the ice-flow dynamics and mass-balance distribution of the area. The negative net surface mass balance in the valley appears to be balanced by the inflow. The flow regime in Scharffenbergbotnen defines four separate mass-balance areas, and about 60 times more ice enters the valley from the northwestern entrance than via the narrow western gate. We formalize and compare three methods of determining both the surface age gradient of the blue ice and the dip angles of isochrones in the firn/blue-ice transition zone: observed and dated radar internal reflections, a geometrical model of isochrones, and output from a flowline model. The geometrical analysis provides generally applicable relationships between ice surface velocity and surface age gradient or isochrone dip angle.

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