Basal channels drive active surface hydrology and transverse ice shelf fracture

Dow, Christine F.; Lee, Won Sang; Greenbaum, J. S.; Greene, Chad A.; Blankenship, D. D.; Poinar, Kristin; Forrest, Alexander L.; Young, D. A.; Zappa, Christopher J.

doi:10.1126/sciadv.aao7212

Cited by 68 publications

(94 citation statements)

References 43 publications

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“…Increases in melt and/or strain rates due to increases in velocity gradients in the future may therefore lead to increased instability and likely collapse of the remaining ice shelves around Greenland [97]. Other metrics of ice shelf state such as ice shelf thickness, areal extent of meltwater ponding and basal melt channelization may prove to be better indicators of ice shelf stability in Greenland, given the different topographic configurations found in Greenland compared to the generally better studied Antarctic ice shelves [94].…”

Section: Resultsmentioning

confidence: 99%

“…It follows that with increasing air temperatures, a higher density of lakes can form increasing the volume of water available for hydro fracturing and causing an increase in the ice tongue instability. However, this effect can be mitigated by drainage of excess water through surface rivers and basal channels [93,94]. Figure 10 therefore only shows the potential effect increasing runoff can have on the stability of the Petermann ice shelf.…”

Section: Calving Front Location and Ice Sheet Mass Budgetmentioning

confidence: 99%

See 1 more Smart Citation

An Integrated View of Greenland Ice Sheet Mass Changes Based on Models and Satellite Observations

Mottram

Simonsen²,

Svendsen³

et al. 2019

Remote Sensing

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The Greenland ice sheet is a major contributor to sea level rise, adding on average 0.47 ± 0.23 mm year − 1 to global mean sea level between 1991 and 2015. The cryosphere as a whole has contributed around 45% of observed global sea level rise since 1993. Understanding the present-day state of the Greenland ice sheet is therefore vital for understanding the processes controlling the modern-day rates of sea level change and for making projections of sea level rise into the future. Here, we provide an overview of the current state of the mass budget of Greenland based on a diverse range of remote sensing observations to produce the essential climate variables (ECVs) of ice velocity, surface elevation change, grounding line location, calving front location, and gravimetric mass balance as well as numerical modelling that together build a consistent picture of a shrinking ice sheet. We also combine these observations with output from a regional climate model and from an ice sheet model to gain insight into existing biases in ice sheet dynamics and surface mass balance processes. Observations show surface lowering across virtually all regions of the ice sheet and at some locations up to −2.65 m year − 1 between 1995 and 2017 based on radar altimetry analysis. In addition, calving fronts at 28 study sites, representing a sample of typical glaciers, have retreated all around Greenland since the 1990s and in only two out of 28 study locations have they remained stable. During the same period, two of five floating ice shelves have collapsed while the locations of grounding lines at the remaining three floating ice shelves have remained stable over the observation period. In a detailed case study with a fracture model at Petermann glacier, we demonstrate the potential sensitivity of these floating ice shelves to future warming. GRACE gravimetrically-derived mass balance (GMB) data shows that overall Greenland has lost 255 ± 15 Gt year − 1 of ice over the period 2003 to 2016, consistent with that shown by IMBIE and a marked increase compared to a rate of loss of 83 ± 63 Gt year − 1 in the 1993–2003 period. Regional climate model and ice sheet model simulations show that surface mass processes dominate the Greenland ice sheet mass budget over most of the interior. However, in areas of high ice velocity there is a significant contribution to mass loss by ice dynamical processes. Marked differences between models and observations indicate that not all processes are captured accurately within models, indicating areas for future research.

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Section: Resultsmentioning

confidence: 99%

Section: Calving Front Location and Ice Sheet Mass Budgetmentioning

confidence: 99%

An Integrated View of Greenland Ice Sheet Mass Changes Based on Models and Satellite Observations

Mottram

Simonsen²,

Svendsen³

et al. 2019

Remote Sensing

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“…The NIS is formed by the adjacent flow of the Reeves and Priestley outlet glaciers (Frezzotti and Mabin, 1994), where its northern boundary abuts the Drygalski ice tongue (DIT) (Figures 1A,B; Khazendar et al, 2001). The NIS is ∼2000 km 2 in area, 200 m thick, with an average ice flow of 0.15 km year −1 (Dow et al, 2018). The adjacent DIT is ∼75 km in length and is the ice shelf of the David Glacier, which has flow speeds ranging from 0.2 to 0.6 km year −1 (Frezzotti and Mabin, 1994).…”

Section: The Nansen Ice Shelf and 2016 Calving Eventmentioning

confidence: 99%

“…to its present extent (Hall, 2009). The NIS is thought to be pinned on multi-year ice near the DIT to the south, and on a topographic high (Inexpressible Island) to the north (Dow et al, 2018; Figures 1C,D).…”

Section: The Nansen Ice Shelf and 2016 Calving Eventmentioning

confidence: 99%

Hydroacoustic, Meteorologic and Seismic Observations of the 2016 Nansen Ice Shelf Calving Event and Iceberg Formation

et al. 2019

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On April 7, 2016 the Nansen ice shelf (NIS) front calved into two icebergs, the first largescale calving event in >30 years. Three hydrophone moorings were deployed seaward of the NIS in December 2015 and over the following months recorded hundreds of short duration, broadband (10-400 Hz) cryogenic signals, likely caused by fracturing of the ice shelf. The majority of these icequakes occurred between January and early March 2016, several weeks prior to the calving observed by satellite on April 7. Barometric pressure and wind speed records show the day the icebergs drifted from the NIS coincided with the largest low-pressure storm system recorded in the previous 7 months. A nearby seismic station also shows an increase in low-frequency energy, harmonic tremor, and microseisms on April 7. Our interpretation is the northern segment of the NIS leading edge broke free during mid-January to February, producing high acoustic energy, but the icebergs remained stationary until a strong low-pressure system with high winds freed the icebergs. As the unpinning of Antarctic ice shelves is not a well-documented process, our observations show that storm systems may play an under-appreciated role in Antarctic ice shelf break-up.

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“…These channels are a surface expression of a sub-ice shelf channel (Le Brocq et al, 2013), also known as basal channel (Marsh et al, 2016;Alley et al, 2016Alley et al, , 2019 or U-channel (Jeofry et al, 2018), most often aligned to the ice flow direction but occasionally migrating across the ice flow direction. As locations of thinner ice these channels can induce ice shelf fracturing (Dow et al, 2018). Thus ice shelf channels potentially influence ice shelf stability, which in turn provides stability of the ice sheet through the buttressing effect (Thomas and MacAyeal, 1982;Fürst et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Subglacial sediment transport upstream of a basal channel in the ice shelf of Support Force Glacier (West Antarctica), identified by reflection seismics

Hofstede

Beyer

Corr

et al. 2020

Preprint

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Abstract. Flow stripes on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the groundling line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel and its upstream continuation on Support Force Glacier which feeds into the Filchner Ice Shelf, West Antarctica. We map the structure of the basal channel at the ice base in the grounded and floating part and identify the subglacial material within the grounded part of the channel and also along the seafloor. Several kilometers upstream of the grounding line we identify a landform, consisting at least in part of sediments, that forms the channel at the ice base. Immediately seaward of the grounding line, the seismic profiles show a 200 m thick partly disturbed, stratified sediment sequence at the seafloor, which we interpret as grounding line deposits. We conclude that the landform hosts the subglacial transport of sediments entering Support Force Glacier at the eastern side of the basal channel. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a very flat topography of the ice shelf base with an almost constant ice thickness gradient along flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction of grounded landforms, ice stream shear margins and subglacial hydrology to form basal channels in ice shelves.

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Basal channels drive active surface hydrology and transverse ice shelf fracture

Abstract: Ice shelf basal channels cause transverse fractures that can be exacerbated by surface rivers, culminating in calving.

Cited by 68 publications

References 43 publications

An Integrated View of Greenland Ice Sheet Mass Changes Based on Models and Satellite Observations

An Integrated View of Greenland Ice Sheet Mass Changes Based on Models and Satellite Observations

Hydroacoustic, Meteorologic and Seismic Observations of the 2016 Nansen Ice Shelf Calving Event and Iceberg Formation

Subglacial sediment transport upstream of a basal channel in the ice shelf of Support Force Glacier (West Antarctica), identified by reflection seismics

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