Recent acceleration of Denman Glacier (1972–2017), East Antarctica, driven by grounding line retreat and changes in ice tongue configuration

Miles, Bertie; Jordan, James; Stokes, Chris R.; Jamieson, Stewart S. R.; Gudmundsson, G. Hilmar; Jenkins, Adrian

doi:10.5194/tc-15-663-2021

Cited by 17 publications

(21 citation statements)

References 67 publications

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“…However, if the bedrock position itself is modified, then the imposed velocity change from flux conservation can be avoided. It is this second approach that we have used throughout this study, in the same fashion as that used by Miles and others (2021) to examine the effect of grounding-line perturbation on instantaneous ice velocity for Denman Glacier. CE-Future : Finally, we also investigate the sensitivity of Cook East to calving-front retreat. To simulate this we remove ice from Cook East's ice shelf by deactivating model nodes in increments relative to a reference line parallel to the calving front and calculate the resulting change in grounding-line flux.…”

Section: Methodsmentioning

confidence: 99%

“…The second step is to use these properties while perturbing aspects of ice geometry (namely, extent, ice-shelf thickness and grounding-line position) to quantify their effect upon modelled ice-flow velocity. This methodology is the same as that used by Miles and others (2021) to investigate the recent acceleration of Denman Glacier by perturbing ice-shelf geometry and grounding line-position and Gudmundsson and others (2019) to investigate the instantaneous response of Antarctic ice velocity to ice-shelf thinning. We justify the use of diagnostic, non-transient simulations here over forward transient simulations because the past observational record of Cook Glacier is both temporally and spatially incomplete.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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The sensitivity of Cook Glacier, East Antarctica, to changes in ice-shelf extent and grounding-line position

et al. 2021

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The Wilkes Subglacial Basin in East Antarctica contains ice equivalent to 3–4 m of global mean sea level rise and is primarily drained by Cook Glacier. Of concern is that recent observations (since the 1970s) show an acceleration in ice speed over the grounding line of both the Eastern and Western portions of Cook Glacier. Here, we use a numerical ice-flow model (Úa) to simulate the instantaneous effects of observed changes at the terminus of Cook Glacier in order to understand the link between these changes and recently observed ice acceleration. Simulations suggest that the acceleration of Cook West was caused by a retreat in calving-front position in the 1970s, potentially enhanced by grounding-line retreat, while acceleration of Cook East was likely caused by ice-shelf thinning and grounding-line retreat in the mid-1990s. Moreover, we show that the instantaneous ice discharge at Cook East would increase by up to 85% if the whole ice shelf is removed and it ungrounds from a pinning point; and that the discharge at Cook West could increase by ~300% if its grounding line retreated by 10 km.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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The sensitivity of Cook Glacier, East Antarctica, to changes in ice-shelf extent and grounding-line position

et al. 2021

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“…The future evolution of this part of the ice sheet critically depends on the evolution of the Totten Glacier, due to its large catchment area and retrograde bedrock slope, promoting instability similar to West Antarctica (Gomez et al, 2010;Durand and Pattyn, 2015;Greenbaum et al, 2015). Comparable conditions apply to the Denman Glacier (Brancato et al, 2020;Smith et al, 2020;Miles et al, 2021). It is the consensus that the evolution of heat transport due to changing ocean currents and ocean temperatures will have a decisive impact on this marine-based part of the ice sheet (Rintoul et al, 2016;Levermann et al, 2020).…”

Section: Relation To Drivers Of Changing Ice Dischargementioning

confidence: 99%

Acceleration of Dynamic Ice Loss in Antarctica From Satellite Gravimetry

et al. 2021

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The dynamic stability of the Antarctic Ice Sheet is one of the largest uncertainties in projections of future global sea-level rise. Essential for improving projections of the ice sheet evolution is the understanding of the ongoing trends and accelerations of mass loss in the context of ice dynamics. Here, we examine accelerations of mass change of the Antarctic Ice Sheet from 2002 to 2020 using data from the GRACE (Gravity Recovery and Climate Experiment; 2002–2017) and its follow-on GRACE-FO (2018-present) satellite missions. By subtracting estimates of net snow accumulation provided by re-analysis data and regional climate models from GRACE/GRACE-FO mass changes, we isolate variations in ice-dynamic discharge and compare them to direct measurements based on the remote sensing of the surface-ice velocity (2002–2017). We show that variations in the GRACE/GRACE-FO time series are modulated by variations in regional snow accumulation caused by large-scale atmospheric circulation. We show for the first time that, after removal of these surface effects, accelerations of ice-dynamic discharge from GRACE/GRACE-FO agree well with those independently derived from surface-ice velocities. For 2002–2020, we recover a discharge acceleration of -5.3 ± 2.2 Gt yr−2 for the entire ice sheet; these increasing losses originate mainly in the Amundsen and Bellingshausen Sea Embayment regions (68%), with additional significant contributions from Dronning Maud Land (18%) and the Filchner-Ronne Ice Shelf region (13%). Under the assumption that the recovered rates and accelerations of mass loss persisted independent of any external forcing, Antarctica would contribute 7.6 ± 2.9 cm to global mean sea-level rise by the year 2100, more than two times the amount of 2.9 ± 0.6 cm obtained by linear extrapolation of current GRACE/GRACE-FO mass loss trends.

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“…Gudmundsson et al, 2012), modern (e.g. Miles et al, 2021), and palaeo (e.g. Jones et al, 2021) ice streams.…”

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confidence: 99%

Nunataks as barriers to ice flow: implications for palaeo ice-sheet reconstructions

Braga¹,

Jones²,

Newall³

et al. 2021

Preprint

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Abstract. Numerical models predict that discharge from the polar ice sheets will become the largest contributor to sea level rise over the coming centuries. However, the predicted amount of ice discharge and associated thinning depends on how well ice sheet models reproduce glaciological processes, such as ice flow in regions of large topographic relief, where ice flows around bedrock summits (i.e. nunataks) and through outlet glaciers. The ability of ice sheet models to capture long-term ice loss is best tested by comparing model simulations against geological data. A benchmark for such models is ice surface elevation change, which has been constrained empirically at nunataks and along margins of outlet glaciers using cosmogenic exposure dating. However, the usefulness of this approach in quantifying ice sheet thinning relies on how well such records represent changes in regional ice surface elevation. Here we examine how ice surface elevations respond to the presence of obstacles that create large topographic relief by modeling ice flow around and between idealised nunataks during periods of imposed ice sheet thinning. We found that, for realistic Antarctic conditions, a single nunatak could exert an impact on ice thickness over 20 km away from its summit, with its most prominent effect being a local increase (decrease) of the ice surface elevation of hundreds of metres upstream (downstream) of the obstacle. A direct consequence of this differential surface response for cosmogenic exposure dating was a delay in the time of bedrock exposure upstream relative to downstream of a nunatak. A nunatak elongated transverse to ice flow, with a wide subglacial continuation, was able to increase ice retention and therefore impose steeper ice surface gradients, while efficient ice drainage through outlet glaciers alleviated the differential response. Such differences, however, are not typically captured by continent-wide ice sheet models due to their coarse grid resolutions. This appears to be a key reason why models overestimate ice-sheet surface elevations and underestimate the pace of ice sheet melt contributing to sea level rise compared to empirical reconstructions. We conclude that a model grid refinement over complex topography and information about sample position relative to ice flow near the nunatak are necessary to improve data-model comparisons of ice surface elevation, and therefore the ability of models to simulate ice discharge in regions of large topographic relief.

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Recent acceleration of Denman Glacier (1972–2017), East Antarctica, driven by grounding line retreat and changes in ice tongue configuration

Cited by 17 publications

References 67 publications

The sensitivity of Cook Glacier, East Antarctica, to changes in ice-shelf extent and grounding-line position

The sensitivity of Cook Glacier, East Antarctica, to changes in ice-shelf extent and grounding-line position

Acceleration of Dynamic Ice Loss in Antarctica From Satellite Gravimetry

Nunataks as barriers to ice flow: implications for palaeo ice-sheet reconstructions

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