scholarly journals Influence of supraglacial lakes and ice-sheet geometry on seasonal ice-flow variability

2013 ◽  
Vol 7 (2) ◽  
pp. 1101-1118 ◽  
Author(s):  
I. Joughin ◽  
S. B. Das ◽  
G. E. Flowers ◽  
M. D. Behn ◽  
R. B. Alley ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Velocity ◽  
Ice Flow ◽  
Bed Topography ◽  
Supraglacial Lakes ◽  
Melt Water ◽  
Flow Enhancement ◽  
Lake Drainage ◽  
Existing Data

Abstract. Supraglacial lakes play an important role in establishing hydrological connections that allow lubricating seasonal melt water to reach the base of the Greenland Ice Sheet. Here we use new surface velocity observations to examine the influence of supraglacial lake drainages and surface melt rate on ice flow. We find large, spatially extensive speedups concurrent with times of lake drainage, showing that lakes play a key role in modulating regional ice flow. While surface meltwater is supplied to the bed via a geographically sparse network of moulins, the observed ice-flow enhancement suggests that this meltwater spreads widely over the ice-sheet bed. We also find that the complex spatial pattern of speedup is strongly determined by the combined influence of bed and surface topography on subglacial water flow. Thus, modeling of ice-sheet basal hydrology likely will require knowledge of bed topography resolved at scales (sub-kilometer) far finer than existing data (several km).

scholarly journals Influence of ice-sheet geometry and supraglacial lakes on seasonal ice-flow variability

2013 ◽  
Vol 7 (4) ◽  
pp. 1185-1192 ◽  
Author(s):  
I. Joughin ◽  
S. B. Das ◽  
G. E. Flowers ◽  
M. D. Behn ◽  
R. B. Alley ◽  
...  
Keyword(s):  
Spatial Pattern ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Velocity ◽  
Ice Flow ◽  
Bed Topography ◽  
Supraglacial Lakes ◽  
Flow Enhancement ◽  
Lake Drainage ◽  
Existing Data

Abstract. Supraglacial lakes play an important role in establishing hydrological connections that allow lubricating seasonal meltwater to reach the base of the Greenland Ice Sheet. Here we use new surface velocity observations to examine the influence of supraglacial lake drainages and surface melt rate on ice flow. We find large, spatially extensive speedups concurrent with times of lake drainage, showing that lakes play a key role in modulating regional ice flow. While surface meltwater is supplied to the bed via a geographically sparse network of moulins, the observed ice-flow enhancement suggests that this meltwater spreads widely over the ice-sheet bed. We also find that the complex spatial pattern of speedup is strongly determined by the combined influence of bed and surface topography on subglacial water flow. Thus, modeling of ice-sheet basal hydrology likely will require knowledge of bed topography resolved at scales (sub-kilometer) far finer than existing data (several km).

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

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.

scholarly journals Characterizing englacial drainage in the ablation zone of the Greenland ice sheet

2008 ◽  
Vol 54 (187) ◽  
pp. 567-578 ◽  
Author(s):  
Ginny A. Catania ◽  
Thomas A. Neumann ◽  
Stephen F. Price
Keyword(s):  
Simulation Model ◽  
Strong Correlation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Velocity ◽  
Ablation Zone ◽  
Moderate Correlation ◽  
Supraglacial Lakes ◽  
Infill Material ◽  
Englacial Drainage

AbstractRapid, local drainage of surface meltwater to the base of the Greenland ice sheet is thought to result in surface velocity variations as far inland as the equilibrium zone (Zwally and others, 2002). Ice-penetrating radar surveys throughout this region allow us to characterize englacial drainage features that appear as vertically stacked diffraction hyperbolae in common-offset profiles. These data are used with a radar-simulation model, which allows for variations in geometry, penetration depth and infill material, to understand the characteristics of these hyperbolae and the likelihood that they are produced by moulins. We find only a moderate correlation between the locations of these possible moulins and supraglacial lakes, indicating that many lakes drain over the surface of the ice sheet, or do not contain sufficient water to reach the bed through moulin formation. We find a strong correlation between moulin location in the ablation region and elevated along-flow tension (due to flow over rough bedrock), which generates surface crevassing and provides an entry point for meltwater. Although theory suggests that moulins may form anywhere on the ice sheet given sufficient meltwater input, our data suggest that they are far more common in the ablation zone than near, or inland from, the equilibrium line.

scholarly journals Bed topography and subglacial landforms in the onset region of the Northeast Greenland Ice Stream

2020 ◽  
Vol 61 (81) ◽  
pp. 143-153 ◽  
Author(s):  
Steven Franke ◽  
Daniela Jansen ◽  
Tobias Binder ◽  
Nils Dörr ◽  
Veit Helm ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ultra Wideband ◽  
Ice Flow ◽  
Detailed Model ◽  
Dynamic Component ◽  
Bed Topography ◽  
Ice Stream ◽  
Topography Model

AbstractThe Northeast Greenland Ice Stream (NEGIS) is an important dynamic component for the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The geometric boundary conditions and in particular the nature of the subglacial bed of the NEGIS are essential to understand its ice flow dynamics. We present a record of more than 8000 km of radar survey lines of multi-channel, ultra-wideband radio echo sounding data covering an area of 24 000 km2, centered on the drill site for the East Greenland Ice-core Project (EGRIP), in the upper part of the NEGIS catchment. Our data yield a new detailed model of ice-thickness distribution and basal topography in the region. The enhanced resolution of our bed topography model shows features which we interpret to be caused by erosional activity, potentially over several glacial–interglacial cycles. Off-nadir reflections from the ice–bed interface in the center of the ice stream indicate a streamlined bed with elongated subglacial landforms. Our new bed topography model will help to improve the basal boundary conditions of NEGIS prescribed for ice flow models and thus foster an improved understanding of the ice-dynamic setting.

Seasonal to multi-annual speedup and slowdown of Greenland outlet glaciers inferred from time-dependent remote sensing observations

2020 ◽  
Author(s):  
Lizz Ultee ◽  
Bryan Riel ◽  
Brent Minchew
Keyword(s):  
Time Series ◽  
Flow Velocity ◽  
Ice Sheet ◽  
Surface Air Temperature ◽  
Greenland Ice Sheet ◽  
Time Dependent ◽  
Surface Velocity ◽  
Short Term ◽  
Ice Flow

<p>The rate of ice flux from the Greenland Ice Sheet to the ocean depends on the ice flow velocity through outlet glaciers. Ice flow velocity, in turn, evolves in response to multiple geographic and environmental forcings at different timescales. For example, velocity may vary daily in response to ocean tides, seasonally in response to surface air temperature, and multi-annually in response to long-term trends in climate. The satellite observations processed as part of the NASA MEaSUREs Greenland Ice Sheet Velocity Map allow us to analyse variations in ice surface velocity at multiple timescales. Here, we decompose short-term and long-term signals in time-dependent velocity fields for Greenland outlet glaciers based on the methods of Riel et al. (2018). Patterns found in short-term signals can constrain basal sliding relations and ice rheology, while the longer-term signals hint at decadal in/stability of outlet glaciers. We present example velocity time series for outlets including Sermeq Kujalleq (Jakobshavn Isbrae) and Helheim Glacier, and we highlight features indicative of dynamic drawdown or advective restabilization. Finally, we comment on the capabilities of a time series analysis software under development for glaciological applications.</p>

scholarly journals Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation

2014 ◽  
Vol 60 (222) ◽  
pp. 647-660 ◽  
Author(s):  
Claudia Ryser ◽  
Martin P. Lüthi ◽  
Lauren C. Andrews ◽  
Matthew J. Hoffman ◽  
Ginny A. Catania ◽  
...  
Keyword(s):  
Dynamical Behavior ◽  
Ice Sheet ◽  
Stress Transfer ◽  
Greenland Ice Sheet ◽  
Good Choice ◽  
Surface Velocity ◽  
Ice Streams ◽  
Ice Flow ◽  
Flow Models ◽  
Dependent Flow

AbstractIce deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44–73% in winter, and up to 90% in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect necessitates the use of high-order ice-flow models, not only in regions of fast-flowing ice streams but in all temperate-based areas of the GrIS. The agreement between modeled and measured deformation rates confirms that the recommended values of the temperature-dependent flow rate factor A are a good choice for ice-sheet models.

scholarly journals Mass balance and ice flow along the north-northwest ridge of the Greenland ice sheet at NorthGRIP

2002 ◽  
Vol 35 ◽  
pp. 521-526 ◽  
Author(s):  
Christine Schøtt Hvidberg ◽  
Kristian Keller ◽  
Niels S. Gundestrup
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Elevation ◽  
Surface Strain ◽  
Surface Velocity ◽  
Ice Flow ◽  
The North ◽  
Ice Flows ◽  
Drilling Site

AbstractThe North Greenland Icecore Project (NorthGRIP) deep drilling site (75˚05’47’’N, 42˚19’42’’ W) is located at the north-northwest ridge of the Greenland ice sheet, 320 km from Summit. A strain net has been established around the NorthGRIP site and surveyed with global positioning system. Our results show that ice flows with a horizontal surface velocity of 1.329 ±0.015ma–1 along the ridge. Estimated principal surface strain rates at NorthGRIP are and in the directions along and transverse to the north-northwest ridge, respectively, i.e. ice is compressed along the ridge but stretched transverse to the ridge. Possible implications of the observed flow pattern for the stratigraphy are discussed. the average thickening rate in the strain-net area is found to be ∂H/∂t = 0.00 ±0.04ma– 1, in agreement with previous estimates of mass balance in high-elevation areas of Greenland.

Seasonally evolving hydraulic transmissivity beneath Greenland supraglacial lakes

2020 ◽  
Author(s):  
Ching-Yao Lai ◽  
Laura Stevens ◽  
Danielle Chase ◽  
Timothy Creyts ◽  
Mark Behn ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Dye Tracing ◽  
Surface Uplift ◽  
Supraglacial Lakes ◽  
Drainage Networks ◽  
Order Of Magnitude ◽  
Novel Method ◽  
Lake Drainage

Abstract Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye-tracing studies indicate that drainage efficiency evolves seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we develop a novel method to infer transmissivity of the drainage system based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes.

scholarly journals Supraglacial lake drainage at a fast-flowing Greenlandic outlet glacier

2019 ◽  
Vol 116 (51) ◽  
pp. 25468-25477 ◽  
Author(s):  
Thomas R. Chudley ◽  
Poul Christoffersen ◽  
Samuel H. Doyle ◽  
Marion Bougamont ◽  
Charlotte M. Schoonman ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Dynamic Responses ◽  
Surface Velocity ◽  
Outlet Glacier ◽  
Direct Observations ◽  
Ice Surface ◽  
Ice Sheet Dynamics ◽  
Lake Drainage

Supraglacial lake drainage events influence Greenland Ice Sheet dynamics on hourly to interannual timescales. However, direct observations are rare, and, to date, no in situ studies exist from fast-flowing sectors of the ice sheet. Here, we present observations of a rapid lake drainage event at Store Glacier, west Greenland, in 2018. The drainage event transported 4.8 × 106m3of meltwater to the glacier bed in ∼5 h, reducing the lake to a third of its original volume. During drainage, the local ice surface rose by 0.55 m, and surface velocity increased from 2.0 m⋅d−1to 5.3 m⋅d−1. Dynamic responses were greatest ∼4 km downstream from the lake, which we interpret as an area of transient water storage constrained by basal topography. Drainage initiated, without any precursory trigger, when the lake expanded and reactivated a preexisting fracture that had been responsible for a drainage event 1 y earlier. Since formation, this fracture had advected ∼500 m from the lake’s deepest point, meaning the lake did not fully drain. Partial drainage events have previously been assumed to occur slowly via lake overtopping, with a comparatively small dynamic influence. In contrast, our findings show that partial drainage events can be caused by hydrofracture, producing new hydrological connections that continue to concentrate the supply of surface meltwater to the bed of the ice sheet throughout the melt season. Our findings therefore indicate that the quantity and resultant dynamic influence of rapid lake drainages are likely being underestimated.

scholarly journals Basal control of supraglacial meltwater catchments on the Greenland Ice Sheet

2018 ◽  
Vol 12 (10) ◽  
pp. 3383-3407 ◽  
Author(s):  
Josh Crozier ◽  
Leif Karlstrom ◽  
Kang Yang
Keyword(s):  
Surface Topography ◽  
Transfer Functions ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Flow Routing ◽  
Ice Flow ◽  
Fluvial Erosion ◽  
Bed Topography ◽  
Ice Surface ◽  
Basal Sliding

Abstract. Ice surface topography controls the routing of surface meltwater generated in the ablation zones of glaciers and ice sheets. Meltwater routing is a direct source of ice mass loss as well as a primary influence on subglacial hydrology and basal sliding of the ice sheet. Although the processes that determine ice sheet topography at the largest scales are known, controls on the topographic features that influence meltwater routing at supraglacial internally drained catchment (IDC) scales (<10s of km) are less well constrained. Here we examine the effects of two processes on ice sheet surface topography: transfer of bed topography to the surface of flowing ice and thermal–fluvial erosion by supraglacial meltwater streams. We implement 2-D basal transfer functions in seven study regions of the western Greenland Ice Sheet ablation zone using recent data sets for bed elevation, ice surface elevation, and ice surface velocities. We find that ∼1–10 km scale ice surface features can be explained well by bed topography transfer in regions with different multiyear-averaged ice flow conditions. We use flow-routing algorithms to extract supraglacial stream networks from 2 to 5 m resolution digital elevation models and compare these with synthetic flow networks calculated on ice surfaces predicted by bed topography transfer. Multiple geomorphological metrics calculated for these networks suggest that bed topography can explain general ∼1–10 km supraglacial meltwater routing and that thermal–fluvial erosion thus has a lesser role in shaping ice surface topography on these scales. We then use bed topography transfer functions and flow routing to conduct a parameter study predicting how supraglacial IDC configurations and subglacial hydraulic potential would change under varying multiyear-averaged ice flow and basal sliding regimes. Predicted changes to subglacial hydraulic flow pathways directly caused by changing ice surface topography are subtle, but temporal changes in basal sliding or ice thickness have potentially significant influences on IDC spatial distribution. We suggest that changes to IDC size and number density could affect subglacial hydrology primarily by dispersing the englacial–subglacial input of surface meltwater.

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