Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages

AbstractSurface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve 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 infer drainage system transmissivity 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 (from 0.8 ± 0.3 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 to 215 ± 90.2 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 ) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input.

Download Full-text

Seasonally evolving hydraulic transmissivity beneath Greenland supraglacial lakes

10.21203/rs.3.rs-104092/v1 ◽

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.

Download Full-text

Discharge of debris from ice at the margin of the Greenland ice sheet

Journal of Glaciology ◽

10.3189/172756502781831359 ◽

2002 ◽

Vol 48 (161) ◽

pp. 192-198 ◽

Cited By ~ 21

Author(s):

Peter G. Knight ◽

Richard I. Waller ◽

Carrie J. Patterson ◽

Alison P. Jones ◽

Zoe P. Robinson

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

High Rate ◽

Outlet Glacier ◽

Tidewater Glaciers ◽

Sediment Production ◽

Basal Ice ◽

Order Of Magnitude ◽

Sediment Transfer ◽

A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

Download Full-text

Seasonal variability in the dynamics of marine-terminating outlet glaciers in Greenland

Journal of Glaciology ◽

10.3189/002214310793146232 ◽

2010 ◽

Vol 56 (198) ◽

pp. 601-613 ◽

Cited By ~ 148

Author(s):

Ian M. Howat ◽

Jason E. Box ◽

Yushin Ahn ◽

Adam Herrington ◽

Ellyn M. McFadden

Keyword(s):

Ice Sheet ◽

Drainage System ◽

Surface Air Temperature ◽

Greenland Ice Sheet ◽

Flow Speed ◽

High Temporal Resolution ◽

Sea Ice Concentration ◽

Seasonal Behavior ◽

Near Surface ◽

Front Position

AbstractRecent studies indicate that the dynamics of fast-flowing, marine-terminating outlet glaciers of the Greenland ice sheet may be sensitive to climate and ocean forcing on sub-annual timescales. Observations of seasonal behavior of these glaciers at such high temporal resolution, however, are currently few. Here we present observations of front position, flow speed, near-surface air temperature and ocean conditions for six large marine-terminating glaciers in the Uummannaq region of West Greenland, to investigate controls on short-term glacier dynamics. As proposed by other studies, we find that seasonal front advance and retreat correlates with the formation and disappearance of an ice melange. Our data suggest that high sea-surface temperature, anomalously low sea-ice concentration and reduced melange formation in early 2003 have triggered multi-year retreat of several glaciers in the study area, which is consistent with other regions in Greenland. Of the stable glaciers, only Rink Isbræ exhibits a seasonal speed variation that correlates with variations in front position, with the others undergoing mid-summer deceleration that indicates the effects of subglacial meltwater discharge and drainage system evolution. Drainage of supraglacial lakes and water-filled crevasses results in substantial decreases in speed (40–60%) on fast-flowing glaciers. Our results demonstrate that attempts to model ice-sheet evolution must take into account short-timescale flow dynamics resulting from drainage events and oceanographic conditions.

Download Full-text

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.

Download Full-text

Remote sounding of Greenland supraglacial melt lakes: implications for subglacial hydraulics

Journal of Glaciology ◽

10.3189/172756507782202883 ◽

2007 ◽

Vol 53 (181) ◽

pp. 257-265 ◽

Cited By ~ 121

Author(s):

Jason E. Box ◽

Kathleen Ski

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Lake Depth ◽

Cross Sectional ◽

Overburden Pressure ◽

Ice Dynamics ◽

Subglacial Environment ◽

Lake Volume ◽

Moderate Resolution Imaging Spectroradiometer ◽

Lake Drainage

AbstractA supraglacial lake-depth retrieval function is developed, based on the correspondence between moderate-resolution imaging spectroradiometer (MODIS) reflectance and water depth measured during raft surveys. Individual lake depth, area and volume statistics, including short-term temporal changes for Greenland’s southwestern ablation region, were compiled for 2000–05. The maximum area of an individual lake was found to be 8.9 km2, the maximum volume 53.0 × 106 m3 and the maximum depth 12.2 m, sampling over 0.0625 km2 pixel areas. The total lake volume reaches >1 km3 in this region by July each year. The importance of melt lake reservoirs to Greenland ice-sheet flow may be a feedback between abrupt lake drainage events and ice dynamics. Lake-outburst volumes up to 31.5 × 106 m3 d−1 are capable of providing sufficient water via moulins to hydraulically pressurize the subglacial environment. Since the overburden pressure at the base of a flooded moulin is greater than that provided by ice, lake-outburst events seem capable of exerting sufficient upward force to lift the ice sheet locally, if water flow in the subglacial environment is constrained laterally. Considering a moulin with a 10 m2 cross-sectional area, basal pressurization can be maintained over lake-outburst episodes lasting hours to days.

Download Full-text

Basal Drainage System Response to Increasing Surface Melt on the Greenland Ice Sheet

Science ◽

10.1126/science.1235905 ◽

2013 ◽

Vol 341 (6147) ◽

pp. 777-779 ◽

Cited By ~ 102

Author(s):

T. Meierbachtol ◽

J. Harper ◽

N. Humphrey

Keyword(s):

Conceptual Models ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

System Response ◽

Mountain Glaciers ◽

In Situ Observations ◽

Key Aspects ◽

Conduit Development

Surface meltwater reaching the bed of the Greenland ice sheet imparts a fundamental control on basal motion. Sliding speed depends on ice/bed coupling, dictated by the configuration and pressure of the hydrologic drainage system. In situ observations in a four-site transect containing 23 boreholes drilled to Greenland’s bed reveal basal water pressures unfavorable to water-draining conduit development extending inland beneath deep ice. This finding is supported by numerical analysis based on realistic ice sheet geometry. Slow meltback of ice walls limits conduit growth, inhibiting their capacity to transport increased discharge. Key aspects of current conceptual models for Greenland basal hydrology, derived primarily from the study of mountain glaciers, appear to be limited to a portion of the ablation zone near the ice sheet margin.

Download Full-text

Evolution of the subglacial drainage system beneath the Greenland Ice Sheet revealed by tracers

Nature Geoscience ◽

10.1038/ngeo1737 ◽

2013 ◽

Vol 6 (3) ◽

pp. 195-198 ◽

Cited By ~ 145

Author(s):

D. M. Chandler ◽

J. L. Wadham ◽

G. P. Lis ◽

T. Cowton ◽

A. Sole ◽

...

Keyword(s):

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Subglacial Drainage

Download Full-text

Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

Biogeosciences Discussions ◽

10.5194/bgd-10-19311-2013 ◽

2013 ◽

Vol 10 (12) ◽

pp. 19311-19345 ◽

Cited By ~ 3

Author(s):

E. C. Lawson ◽

J. L. Wadham ◽

M. Tranter ◽

M. Stibal ◽

G. P. Lis ◽

...

Keyword(s):

Organic Carbon ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

River System ◽

The Arctic ◽

Marine Microorganisms ◽

The North ◽

Glacial Runoff ◽

Order Of Magnitude ◽

Free Carbohydrates

Abstract. Runoff from small glacier systems contains dissolved organic carbon (DOC), rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr−1). We report high and episodic fluxes of POC and DOC from a large (1200 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70–89% on average), is sourced from the ice sheet bed and contains a significant bioreactive component (9% carbohydrates). A major source for the "bioavailable" (free carbohydrates) LMW-DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW-DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (30–58%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the ~ 2 fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating supply-limitation of suspended sediment in runoff. Scaled to the GrIS, the combined DOC and POC fluxes (0.13–0.17 Tg C yr−1 DOC, 0.36–1.52 Tg C yr−1 mean POC) are of a similar order of magnitude to a large Arctic river system, and hence represent an important OC source to the North Atlantic, Greenland and Labrador Seas.

Download Full-text

Surface mass budget and meltwater discharge from the Kangerlussuaq sector of the Greenland ice sheet during record-warm year 2010

The Cryosphere Discussions ◽

10.5194/tcd-5-2319-2011 ◽

2011 ◽

Vol 5 (5) ◽

pp. 2319-2347 ◽

Cited By ~ 2

Author(s):

D. van As ◽

A. Hubbard ◽

B. Hasholt ◽

A. B. Mikkelsen ◽

M. van den Broeke ◽

...

Keyword(s):

High Temperatures ◽

Time Lag ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Western Coast ◽

Positive Anomaly ◽

Ablation Zone ◽

Surface Mass ◽

Average Temperature

Abstract. The year 2010 has been anomalously warm in most of Greenland, most notably in the south and along the western coast. Our study targets the Kangerlussuaq region around 67° N in Southwest Greenland, where the temperature anomalies were record setting. In 2010, the average temperature was 5 °C (2.7 standard deviations) above the 1974–2010 average in the town of Kangerlussuaq. High temperatures were also observed over the ice sheet, with the positive anomaly increasing with altitude. Also surface albedo, from calibrated MODIS measurements, was anomalously low in 2010, chiefly in the upper ablation zone. The low albedo was caused by the high ablation in 2010, which profited in turn from high temperatures, low albedo, and of low wintertime accumulation. The largest melt excess (166%) was found in the upper ablation zone, where higher temperatures and lower albedo contributed equally to the melt anomaly. In total, we estimate that 6.6 km3 of surface meltwater ran off the ice sheet in the Kangerlussuaq catchment area in 2010, exceeding "normal" year 2009 by 145%. When compared to discharge estimated from discharge measurements in the proglacial river we find good agreement. The time lag between the records is caused by storage within and underneath the ice sheet, and suggests adaption of the subglacial drainage system to meltwater availability, with more efficient drainage occurring after the peak of the melt season.

Download Full-text