The impact of glacier geometry on meltwater plume structure and submarine melt in Greenland fjords

Carroll, Dustin; Sutherland, David A.; Hudson, B.; Moon, Twila; Catania, G. A.; Shroyer, Emily L.; Nash, Jonathan D.; Bartholomaus, T. C.; Felikson, Denis; Stearns, L. A.; Noël, Brice; Broeke, M. R. van den

doi:10.1002/2016gl070170

Cited by 126 publications

(201 citation statements)

References 64 publications

(69 reference statements)

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“…The glacier releases subglacial discharge via two large channels, but their corresponding melting contributes only 15 % of the total melt of the glacier front. Furthermore, Carroll et al (2016) showed that the simulated melt rate of a single cone plume is about 2 orders of magnitudes lower than the spatially averaged melt rate by Fried et al (2015). Thus we investigate whether the LP model can calculate the average melting by assuming that the 250 m deep glacier is undercut below 50 meters depth, with an angle of 77 • to achieve the observed undercutting (Fig.…”

Section: West Greenland Glaciersmentioning

confidence: 99%

Simple models for the simulation of submarine melt for a Greenland glacial system model

2018

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Abstract. Two hundred marine-terminating Greenland outlet glaciers deliver more than half of the annually accumulated ice into the ocean and have played an important role in the Greenland ice sheet mass loss observed since the mid1990s. Submarine melt may play a crucial role in the mass balance and position of the grounding line of these outlet glaciers. As the ocean warms, it is expected that submarine melt will increase, potentially driving outlet glaciers retreat and contributing to sea level rise. Projections of the future contribution of outlet glaciers to sea level rise are hampered by the necessity to use models with extremely high resolution of the order of a few hundred meters. That requirement in not only demanded when modeling outlet glaciers as a stand alone model but also when coupling them with highresolution 3-D ocean models. In addition, fjord bathymetry data are mostly missing or inaccurate (errors of several hundreds of meters), which questions the benefit of using computationally expensive 3-D models for future predictions. Here we propose an alternative approach built on the use of a computationally efficient simple model of submarine melt based on turbulent plume theory. We show that such a simple model is in reasonable agreement with several available modeling studies. We performed a suite of experiments to analyze sensitivity of these simple models to model parameters and climate characteristics. We found that the computationally cheap plume model demonstrates qualitatively similar behavior as 3-D general circulation models. To match results of the 3-D models in a quantitative manner, a scaling factor of the order of 1 is needed for the plume models. We applied this approach to model submarine melt for six representative Greenland glaciers and found that the application of a line plume can produce submarine melt compatible with observational data. Our results show that the line plume model is more appropriate than the cone plume model for simulating the average submarine melting of real glaciers in Greenland.

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Section: West Greenland Glaciersmentioning

confidence: 99%

Simple models for the simulation of submarine melt for a Greenland glacial system model

2018

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“…Subglacial discharge exits the glacier at the grounding line, rises buoyantly along the ice front due to its lower density relative to the ambient fjord water, and flows down-fjord once neutral buoyancy is reached (Motyka et al, 2003;Jenkins, 2011;Cowton et al, 2015). In fjords with shallow glacier grounding line depths (<500 m) like KNS, summer discharge meltwater plumes often reach neutral buoyancy and horizontally enter the fjord within the upper 100 m of the water column (Carroll et al, 2016). The outflow forced by the subglacial discharge establishes an estuarine circulation cell, drawing in coastal waters from the shelf, which flow in a layer beneath the fresher outflow (Motyka et al, 2003;Mortensen et al, 2011).…”

Section: Study Areamentioning

confidence: 99%

“…Although producing weak plumes, subglacial discharge of this magnitude can generate point source SMRs of between 2 and 4 m d −1 . Due to their lower velocity, weak plumes, such as those expected via basal frictional melting, reach neutral buoyancy before reaching the fjord surface (Christoffersen et al, 2012;Slater et al, 2015;Carroll et al, 2016). However, close to the glacier grounding line, where ice tongue keel depth is greatest, weaker plumes will likely still reach and melt the base of the ice tongue.…”

Section: Temporal Variability In Smrmentioning

confidence: 99%

Estimating Spring Terminus Submarine Melt Rates at a Greenlandic Tidewater Glacier Using Satellite Imagery

et al. 2017

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Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at tidewater glaciers, with submarine melting proposed as a potential trigger of increased glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d −1 near the glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d −1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at tidewater glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.

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“…). Yet ice sheet catchment delineation remains a relatively uncertain undertaking, e.g., due to uncertainties in bedrock topographical maps (Carroll et al, 2016) that were minimized by Lindbäck et al (2015) by constructing a detailed bedrock map from ice-penetrating radar measurements. To our advantage, the Kangerlussuaq catchment is relatively wide at 30+ km near the ice sheet margin (Fig.…”

Section: Surface Mass Balance Modelingmentioning

confidence: 99%

Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

Mikkelsen²,

Nielsen³

et al. 2017

The Cryosphere

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Abstract. Concurrent ice sheet surface runoff and proglacial discharge monitoring are essential for understanding Greenland ice sheet meltwater release. We use an updated, wellconstrained river discharge time series from the Watson River in southwest Greenland, with an accurate, observation-based ice sheet surface mass balance model of the ∼ 12 000 km 2 ice sheet area feeding the river. For the 2006-2015 decade, we find a large range of a factor of 3 in interannual variability in discharge. The amount of discharge is amplified ∼ 56 % by the ice sheet's hypsometry, i.e., area increase with elevation. A good match between river discharge and ice sheet surface meltwater production is found after introducing elevationdependent transit delays that moderate diurnal variability in meltwater release by a factor of 10-20. The routing lag time increases with ice sheet elevation and attains values in excess of 1 week for the upper reaches of the runoff area at ∼ 1800 m above sea level. These multi-day routing delays ensure that the highest proglacial discharge levels and thus overbank flooding events are more likely to occur after multiday melt episodes. Finally, for the Watson River ice sheet catchment, we find no evidence of meltwater storage in or release from the en-and subglacial environments in quantities exceeding our methodological uncertainty, based on the good match between ice sheet runoff and proglacial discharge.

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The impact of glacier geometry on meltwater plume structure and submarine melt in Greenland fjords

Cited by 126 publications

References 64 publications

Simple models for the simulation of submarine melt for a Greenland glacial system model

Simple models for the simulation of submarine melt for a Greenland glacial system model

Estimating Spring Terminus Submarine Melt Rates at a Greenlandic Tidewater Glacier Using Satellite Imagery

Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release

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