Evidence from ice shelves for channelized meltwater flow beneath the Antarctic Ice Sheet

Brocq, A. M. Le; Ross, Neil; Griggs, J. A.; Bingham, Robert G.; Corr, Hugh; Ferraccioli, Fausto; Jenkins, Adrian; Jordan, Tom A.; Payne, Antony J.; Rippin, David M.; Siegert, Martín J.

doi:10.1038/ngeo1977

Cited by 183 publications

(245 citation statements)

References 28 publications

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“…4). Almost all ice shelf channels at RBIS are connected to the grounding line and may arise from water-filled subglacial conduits injecting subglacial melt water into the ice shelf cavity, driving a spatially localized buoyant melt water plume (Jenkins, 2011;Le Brocq et al, 2013;Drews et al, 2017;Sergienko, 2013). Such localized melting near the grounding zone has been previously observed on Pine Island Ice Shelf using similar methods as done here (Dutrieux et al, 2013).…”

Section: Discussionmentioning

confidence: 66%

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

et al. 2017

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Abstract. Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique -based on satellite observations -to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmosphericmodel surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from −14.7 to 8.6 m a −1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) lowers by 0.5 to 1.4 m a −1 , which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.

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Section: Discussionmentioning

confidence: 66%

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

et al. 2017

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“…Common to all is melting of the ice shelf base which, combined with perturbations in the basal topography, allows the melt to concentrate and form channels. An initial basal topography could come from existing undulations in ice thickness at the grounding line [Gladish et al, 2012], lateral shear at the ice-shelf boundaries [Sergienko, 2013], or outflow of channelized continental subglacial water at the grounding line [Le Brocq et al, 2013]. The latter study presents evidence for large channels at the grounding line of the Filchner-Ronne and Ross ice shelves as well as under a number of smaller ice shelves around East Antarctica.…”

Section: Introductionmentioning

confidence: 72%

Complex network of channels beneath an Antarctic ice shelf

Langley

Deschwanden

Kohler

et al. 2014

Geophysical Research Letters

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Ice shelves play an important role in stabilizing the interior grounded ice of the large ice sheets.The thinning of major ice shelves observed in recent years, possibly in connection to warmer ocean waters coming into contact with the ice-shelf base, has focused attention on the ice-ocean interface. Here we reveal a complex network of sub ice-shelf channels under the Fimbul Ice Shelf, Antarctica, mapped using ground-penetrating radar over a 100 km 2 grid. The channels are 300-500 m wide and 50 m high, among the narrowest of any reported. Observing narrow channels beneath an ice shelf that is mainly surrounded by cold ocean waters, with temperatures close to the surface freezing point, shows that channelized basal melting is not restricted to rapidly melting ice shelves, indicating that spatial melt patterns around Antarctica are likely to vary on scales that are not yet incorporated in ice-ocean models.

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“…A number of ice shelves have been observed to have channel-like incisions at their base, oriented roughly in the direction of ice flow (Rignot & Steffen 2008;Bindschadler et al 2011;Vaughan et al 2012;LeBrocq et al 2013). Observationally inferred basal melt rates are enhanced within the channels compared to the neighbouring thicker ice (Rignot & Steffen 2008;Dutrieux et al 2013), and plumes containing a mixture of entrained warm deep waters and ice shelf melt have been observed to emerge from under Pine Island ice shelf in the vicinity of larger channels (Mankoff et al 2012).…”

Section: Introductionmentioning

confidence: 95%

Channelization of plumes beneath ice shelves

2015

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We study a simplified model of ice-ocean interaction beneath a floating ice shelf, and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line. The model combines an extensional thin-film description of viscous ice flow in the shelf, with melting at its base driven by a turbulent ocean plume. Small transverse perturbations to the one-dimensional steady state are considered, driven either by ice thickness or subglacial discharge variations across the grounding line. Either forcing leads to the growth of channels downstream, with melting driven by locally enhanced ocean velocities, and thus heat transfer. Narrow channels are smoothed out due to turbulent mixing in the ocean plume, leading to a preferred wavelength for channel growth. In the absence of perturbations at the grounding line, linear stability analysis suggests that the one dimensional state is stable to initial perturbations, chiefly due to the background ice advection.

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Evidence from ice shelves for channelized meltwater flow beneath the Antarctic Ice Sheet

Cited by 183 publications

References 28 publications

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

Complex network of channels beneath an Antarctic ice shelf

Channelization of plumes beneath ice shelves

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