Quantifying supraglacial meltwater pathways in the Paakitsoq region, West Greenland

ABSTRACTIncreased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the subglacial environment. However, spatial patterns of surface input and partitioning of meltwater between different pathways to the base remain poorly understood. To further our understanding of surface drainage, we apply a supraglacial hydrology model to the Paakitsoq region, West Greenland for three contrasting melt seasons. During an average melt season, crevasses drain ~47% of surface runoff, lake hydrofracture drains ~3% during the hydrofracturing events themselves, while the subsequent surface-to-bed connections drain ~21% and moulins outside of lake basins drain ~15%. Lake hydrofracture forms the primary drainage pathway at higher elevations (above ~850 m) while crevasses drain a significant proportion of meltwater at lower elevations. During the two higher intensity melt seasons, model results show an increase (~5 and ~6% of total surface runoff) in the proportion of runoff drained above ~1300 m relative to the melt season of average intensity. The potential for interannual changes in meltwater partitioning could have implications for how the dynamics of the ice sheet respond to ongoing changes in meltwater production.

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Topographic and Glaciological Controls on Holocene Ice-Sheet Margin Dynamics. Central West Greenland

Annals of Glaciology ◽

10.3189/s0260305500008806 ◽

1990 ◽

Vol 14 ◽

pp. 307-310 ◽

Cited By ~ 11

Author(s):

C.R. Warren ◽

N.R.J. Hulton

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Glacial Maximum ◽

Warm Climate ◽

Short Term ◽

The West ◽

West Greenland ◽

The Past

The retreat of the West Greenland ice sheet from its Sisimiut (Wisconsinan) glacial maximum, was punctuated by a series of Stillstands or small readvances that formed numerous moraines. These landforms have been interpreted in the past as the result of short-term, regional falls in ablation-season temperatures. However, mapping of the geomorphological evidence south of Ilulissat (Jakobshavn) suggests that retreat behaviour was not primarily governed by climate, and therefore that the former ice margins are not palaeoclimatically significant. During warm climate ice-sheet wastage, the successive quasi-stable positions adopted by the ice margin were largely governed by topography. The retreat of the inherently unstable calving glaciers was arrested only at topographically-determined locations where stability could be achieved.

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Firn temperature and meltwater refreezing in the lower accumulation area of the Greenland ice sheet, Pâkitsoq, West Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v159.8218 ◽

1993 ◽

Vol 159 ◽

pp. 109-114

Author(s):

R.J Braithwaite

Keyword(s):

Sea Level ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

International Project ◽

Sea Level Changes ◽

West Greenland ◽

Degree Day ◽

Air Temperatures ◽

Surface Melt ◽

High Degree

Firn temperatures and meltwater refreezing are studied in the lower accumulation area of the Greenland ice sheet as part of an international project on sea level changes. In the study area, 1440–1620 m a.s.l., meltwater penetrates several metres into the firn and refreezes, warming the firn by 5–7°C compared with annual air temperatures. This firn warming is closely related to surface melt which can be estimated by several methods. A relatively high degree-day factor is needed to account for the melt rates found.

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Assessing ice margin fluctuations on differing timescales: Chronological constraints from Sermeq Kujatdleq and Nordenskiöld Gletscher, central West Greenland

The Holocene ◽

10.1177/0959683618761541 ◽

2018 ◽

Vol 28 (7) ◽

pp. 1160-1172 ◽

Cited By ~ 2

Author(s):

Samuel E Kelley ◽

Jason P Briner ◽

Sandy L O’Hara

Keyword(s):

Late Holocene ◽

Sediment Cores ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Dynamics ◽

West Greenland ◽

Southern Site ◽

Ice Velocity ◽

Observational Record ◽

Local Variability

The observational record of ice margin position reveals asynchrony in both the timing and magnitude of Greenland Ice Sheet (GrIS) margin fluctuations and illustrates the complex reactions of ice sheets to climatic perturbations. In this study, we reconstruct the timing and pattern of middle- and late-Holocene GrIS margin fluctuations at two locations, ~190 km apart, in central West Greenland using radiocarbon-dated sediment cores from proglacial-threshold lakes. Our results demonstrate that deglaciation occurs at both sites during the early Holocene, with the ice sheet remaining in a smaller-than-present ice margin configuration until ~500 years ago when it readvanced into lake catchments at both sites. At our northern site, Sermeq Kujatdleq, the late-Holocene advance of the GrIS approached maximum position during the past 280 years, with the culmination of the advance occurring at AD 1992–1994, and modern retreat was underway by AD 1998–2001. In contrast, field and observational evidence suggest that the GrIS at our southern site, Nordenskiöld Gletscher, has been advancing or stable throughout the 20th century. These results, in conjunction with previous work in the region, highlight the asynchronous nature of late-Holocene advances and subsequent modern retreat, implying that local variability, such as ice velocity or ice dynamics, is responsible for modulating ice margin response to changes in climate on these decadal to centennial timescales. Additional high-resolution records of past ice sheet fluctuations are needed to inform and more accurately constrain our predictions of future cryosphere response to changes in climate.

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Freshwater input into a low-Arctic Fjord in West Greenland: Timing, drivers and model evaluation

10.5194/egusphere-egu21-14149 ◽

2021 ◽

Author(s):

Jakob Abermann ◽

Kirsty Langley ◽

Sille Myreng ◽

Dorthe Petersen ◽

Kerstin Rasmussen ◽

...

Keyword(s):

Large Scale ◽

Temporal Trends ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Base Flow ◽

Minor Role ◽

Freshwater Flux ◽

Freshwater Input ◽

West Greenland ◽

Specific Discharge

<p>The majority of the freshwater input from Greenland stems from the Greenland Ice Sheet. Despite its importance in terms of freshwater totals, there is a much higher number of individual catchments disconnected from the ice sheet contributing on average about 26% of the total Greenland freshwater flux. Most of those catchments have local glacier cover, only very few of them are instrumented and little scientific literature exists. We present a dataset of 12 years of discharge of four catchments less than 15 km apart, that are different in size (between 7 and 32 km&#178;), local glacier coverage (4-11%) and lake cover (0-5%). They all drain into Kobbefjord, a well-studied fjord in West Greenland, near Greenland&#8217;s capital Nuuk. We find that annual specific discharge totals vary greatly (between 1.2 and 1.9 m/yr on a 12-year average within 15 km) due to a general climatic gradient and different strengths of orographic shading. The seasonal cycle differs among the sites mainly due to different exposure to solar radiation as a driver for major snowmelt; small ice coverage in the catchments plays only a minor role in discharge variability. Dry years generally increase the magnitude of spatial gradients in specific discharge and no significant temporal trends have been found in the studied catchments. On the sub-daily scale, the presence and elevation of lakes determines the catchment&#8217;s response during sunny days, leading to a difference in the timing of maximum discharge of between 7 and 12 hours depending on the site and the time of the year. The response of discharge to major precipitation events is discussed, where uniform reaction is found for the catchments with no lakes near the gauge and a delay of between 5 and 7 hours in the catchment with low-lying lakes. A comparison with a recently published modelled discharge time series on individual catchment scale shows the model&#8217;s capability of reproducing both snowmelt and large-scale storm events; however, the strong spatial heterogeneity of discharge magnitude and timing as well as the presence and variability of base-flow is not captured. We discuss methods to combine observational data with existing model output in order to improve the potential of their combined usage on the Greenland-scale.</p>

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Direct measurements of meltwater runoff on the Greenland ice sheet surface

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1707743114 ◽

2017 ◽

Vol 114 (50) ◽

pp. E10622-E10631 ◽

Cited By ~ 28

Author(s):

Laurence C. Smith ◽

Kang Yang ◽

Lincoln H Pitcher ◽

Brandon T. Overstreet ◽

Vena W. Chu ◽

...

Keyword(s):

Sea Level ◽

Surface Runoff ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Dynamics ◽

Sheet Surface ◽

Ice Surface ◽

Meltwater Runoff ◽

Direct Measurements ◽

Peak Discharges

Meltwater runoff from the Greenland ice sheet surface influences surface mass balance (SMB), ice dynamics, and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream fluvial catchment area. A first 72-h trial for a 63.1-km2moulin-terminating internally drained catchment (IDC) on Greenland’s midelevation (1,207–1,381 m above sea level) ablation zone is compared with melt and runoff simulations from HIRHAM5, MAR3.6, RACMO2.3, MERRA-2, and SEB climate/SMB models. Current models cannot reproduce peak discharges or timing of runoff entering moulins but are improved using synthetic unit hydrograph (SUH) theory. Retroactive SUH applications to two older field studies reproduce their findings, signifying that remotely sensed IDC area, shape, and supraglacial river length are useful for predicting delays in peak runoff delivery to moulins. Applying SUH to HIRHAM5, MAR3.6, and RACMO2.3 gridded melt products for 799 surrounding IDCs suggests their terminal moulins receive lower peak discharges, less diurnal variability, and asynchronous runoff timing relative to climate/SMB model output alone. Conversely, large IDCs produce high moulin discharges, even at high elevations where melt rates are low. During this particular field experiment, models overestimated runoff by +21 to +58%, linked to overestimated surface ablation and possible meltwater retention in bare, porous, low-density ice. Direct measurements of ice surface runoff will improve climate/SMB models, and incorporating remotely sensed IDCs will aid coupling of SMB with ice dynamics and subglacial systems.

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Potential positive feedback between Greenland Ice Sheet melt and Baffin Bay heat content on the west Greenland shelf

Geophysical Research Letters ◽

10.1002/2015gl064626 ◽

2015 ◽

Vol 42 (12) ◽

pp. 4922-4930 ◽

Cited By ~ 20

Author(s):

Laura Castro de la Guardia ◽

Xianmin Hu ◽

Paul G. Myers

Keyword(s):

Positive Feedback ◽

Ice Sheet ◽

Heat Content ◽

Greenland Ice Sheet ◽

The West ◽

Baffin Bay ◽

West Greenland

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Characteristics of the lower ablation zone of the West Greenland ice sheet for energy-balance modelling

Annals of Glaciology ◽

10.1017/s0260305500013392 ◽

1996 ◽

Vol 23 ◽

pp. 160-166 ◽

Cited By ~ 19

Author(s):

Michiel van den Broeke

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Global Radiation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Longwave Radiation ◽

Turbulent Fluxes ◽

Ablation Zone ◽

The West ◽

West Greenland

In this paper, we present the summer-time energy balance for a site in the lower ablation zone of the West Greenland ice sheet. The summer climate of this part of Greenland is sunny and dry. The energy that is available for melting (on average 174 W m−2or 4.5 cm w.e.d−1) is mainly provided by net global radiation two-thirds and sensible-heat flux (one-third). The contribution of the sub-surface heat flux, the latent-heat flux and the net longwave radiation to the energy balance are small. We tested some parameterizations to calculate energy-balance components that are currently used in general circulation models, energy-balance models and mesoscale meteorological models. For the area and time period under consideration, parameterizations that use screen-level temperature for the calculation of incoming longwave radiation systematically underestimate this quantity by 10 W m−2owing to the proximity of the melting-ice surface that restricts temperature increase of the lowest air layers. The incoming global radiation was predicted correctly. Simple explicit schemes that calculate the stability corrections for turbulent fluxes as a function of the bulk Richardson number tend to underestimate the turbulent fluxes by 15 W m−2. The aerodynamic roughness lengthz0derived from wind-speed profiles appears to be erroneously small, leading to underestimation of the fluxes by 30 W m−2. Probably, the wind profile is distorted by the rough terrain. An estimate ofz0biased on microtopographical survey yielded a more realistic result. Because all errors work in the same direction, the use of some of the parameterizations can cause serious underestimation of the melting energy.

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Simulation of Run-Off from the Greenland Ice Sheet for Planning Hydro-Electric Power, Ilulissat/Jakobshavn, West Greenland

Annals of Glaciology ◽

10.1017/s0260305500007540 ◽

1989 ◽

Vol 13 ◽

pp. 12-15 ◽

Cited By ~ 9

Author(s):

Roger J. Braithwaite ◽

Henrik Højmark Thomsen

Keyword(s):

Electric Power ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Climatic Conditions ◽

Electric Power Station ◽

Hydroelectric Power ◽

Drainage Pattern ◽

West Greenland ◽

Run Off ◽

Hydraulic Conditions

Simulations of run-off from the Greenland ice sheet were made as part of a feasibility study for provision of hydroelectric power for Ilulissat/Jakobshavn, West Greenland. The aims were to see if the available short series of run-off measurements are typical of those under present climatic conditions, and to assess possible changes in run-off likely to be caused by gross changes in drainage pattern on the ice sheet. Specific run-off was calculated from climatological data, whilst run-off volumes were calculated by integrating specific run-off over the area of the ice sheet. There have been substantial year-to-year variations in run-off, but the 6 year measurement period is reasonably representative of present climatic conditions. Run-off could be reduced by 21% as a result of changes in hydraulic conditions on the ice sheet without this having a significant effect on the economy of the planned hydro-electric power station.

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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.

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