Distributed subglacial discharge drives significant submarine melt at a Greenland tidewater glacier

Fried, M.; Catania, G. A.; Bartholomaus, T. C.; Duncan, D.; Davis, M. B.; Stearns, L. A.; Nash, Jonathan D.; Shroyer, Emily L.; Sutherland, David A.

doi:10.1002/2015gl065806

Cited by 165 publications

(231 citation statements)

References 34 publications

(58 reference statements)

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“…8d) creates an undercut profile concentrated right near the waterline. Fried et al (2015) found similar results when modelling melt rates at shallow grounding lines (100-250 m) given 250 m 3 s −1 discharge. It is interesting to see that the observed front after calving, F obs i (dashed line in Fig.…”

Section: Undercuttingsupporting

confidence: 65%

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

et al. 2018

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Abstract. In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process by combining six different models in an offlinecoupled workflow: a continuum-mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple subglacial hydrology model, a plume model, an undercutting model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We demonstrate the feasibility of reproducing the observed calving retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season by using the output from the first five models as input to HiDEM. Basal sliding and glacier motion are addressed using Elmer/Ice, while calving is modelled by HiDEM. A hydrology model calculates subglacial drainage paths and indicates two main outlets with different discharges. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge locations during the melting season. Calving rates are also influenced by basal friction, through its effects on near-terminus strain rates and ice velocity.

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Section: Undercuttingsupporting

confidence: 65%

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

et al. 2018

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“…First, we analyse the sensitivity of the model to different constant (in space and time) B ref values applied at the base of the ice-sheet marine margins. Due to the scarcity of submarine melt observations along the GrIS coasts, and since the only available estimates have focused on few very rapid tidewater Greenland glaciers that cannot be representative of the basal melt rate for the entirety of GrIS marine areas (Rignot et al, 2010;Motyka et al, 2011;Straneo et al, 2012;Xu et al, 2013;Enderlin and Howat, 2013;Fried et al, 2015;Rignot et al, 2016;Wilson et al, 2017), we assume presentday basal melting rates for Greenland comparable to those from Antarctic ice shelves . The range of values of B ref is set between 0 and 40 m a −1 , while κ is set to zero to make the ocean contribution constant in time.…”

Section: Experimental Designmentioning

confidence: 99%

The sensitivity of the Greenland Ice Sheet to glacial–interglacial oceanic forcing

et al. 2018

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Abstract.Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speedup of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheetshelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial-interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.

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“…In the future, more comprehensive mooring arrays, perhaps coupled with new methods for estimating submarine melting (e.g. from imaging of glacier fronts, Rignot et al, 2015;Fried et al, 2015), could provide a path forward for better constraining the freshwater fluxes. Additionally, icebergs might be a significant source of submarine melting in fjords, obscuring the glacier melt-rate and requiring new methods to partition glacier and iceberg melting if glacier melt rates are to be estimated from oceanic measurements.…”

Section: Discussionmentioning

confidence: 99%

“…For example, the measurements from Fried et al (2015) show terminus undercutting due to submarine melting, which has been suggested to enhance calving Bartholomaus et al, 2013) and thus present a mechanism for submarine melting to trigger dynamic glacier changes.…”

Section: Future Directionsmentioning

confidence: 99%

“…In the future, combining oceanic observations with independent glaciological measurements could improve our understanding of submarine melt rates or reveal the mysterious path of subglacial discharge as it transits under the glacier and then mixes into the fjord. In particular, recent studies have used repeat side-scan sonar surveys to measure the morphology of submarine termini and estimate melt rates (Fried et al, 2015;Rignot et al, 2015). Independent estimates of submarine meltwater from oceanic budgets and side-scan sonar could test the accuracy of the different approaches to quantifying meltwater fluxes.…”

Section: Future Directionsmentioning

confidence: 99%

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Dynamics of Greenland�s glacial fjords

Jackson¹

2016

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Glacial fjords form conduits between glaciers of the Greenland Ice Sheet and the North Atlantic. They are the gateways for importing oceanic heat to melt ice and for exporting meltwater into the ocean. Submarine melting in fjords has been implicated as a driver of recent glacier acceleration; however, there are no direct measurements of this melting, and little is known about the fjord processes that modulate melt rates. Combining observations, theory, and modeling, this thesis investigates the circulation, heat transport, and meltwater export in glacial fjords.While most recent studies focus on glacial buoyancy forcing, there are other drivers -e.g. tides, local wind, shelf variability -that can be important for fjord circulation. Using moored records from two major Greenlandic fjords, shelf forcing (from shelf density fluctuations) is found to dominate the fjord circulation, driving rapid exchange with the shelf and large heat content variability near the glacier. Contrary to the conventional paradigm, these flows mask any glacier-driven circulation in the non-summer months. During the summer, when shelf forcing is reduced and freshwater forcing peaks, a mean exchange flow transports warm Atlantic-origin water towards the glacier and exports glacial meltwater.Many recent studies have inferred submarine melt rates from oceanic heat transport, but the fjord budgets that underlie this method have been overlooked. Building on estuarine studies of salt fluxes, this thesis presents a new framework for assessing glacial fjord budgets and revised equations for inferring meltwater fluxes. Two different seasonal regimes are found in the heat/salt budgets for Sermilik Fjord, and the results provide the first time-series of submarine meltwater and subglacial discharge fluxes into a glacial fjord.Finally, building on the observations, ROMS numerical simulations and two analytical models are used to investigate the dynamics of shelf-driven flows and their importance relative to local wind forcing across the parameter space of Greenland's fjords. The fjord response is found to vary primarily with the width relative to the deformation radius and the fjord adjustment timescale relative to the forcing timescale. Understanding these modes of circulation is a step towards accurate modeling of ocean-glacier interactions.

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Distributed subglacial discharge drives significant submarine melt at a Greenland tidewater glacier

Cited by 165 publications

References 34 publications

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

The sensitivity of the Greenland Ice Sheet to glacial–interglacial oceanic forcing

Dynamics of Greenland�s glacial fjords

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