Thickness of the divide and flank of the West Antarctic Ice Sheet through the last deglaciation

Spector, Perry; Stone, John O.; Goehring, Brent M.

doi:10.5194/tc-13-3061-2019

Cited by 18 publications

(13 citation statements)

References 51 publications

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“…Our estimate is broadly in agreement with LGM ice sheet reconstructions that suggest a West-East ∆z contrast between 160 and 560 m (10). Although the implied ∆z at WAIS exceeds the observed highstand at ice margin nunataks (23), such data do not strongly constrain the elevation at WD over 500 km away.…”

mentioning

confidence: 67%

Antarctic surface temperature and elevation during the Last Glacial Maximum

Buizert

Fudge

Roberts

et al. 2021

Science

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Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with the use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations.

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mentioning

confidence: 67%

Antarctic surface temperature and elevation during the Last Glacial Maximum

Buizert

Fudge

Roberts

et al. 2021

Science

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“…to assess the model's ability to reproduce the geological record). In light of our results, it is understandable that experiments using a regular grid at these resolutions struggle to closely match ice surface elevation over mountainous regions reconstructed from cosmogenic exposure dating, and do not fully capture their recorded timing and magnitude of ice thinning (Spector et al, 2019;Stutz et al, 2020). In our experiments, a grid-cell size smaller than the glacier width manages to capture the drainage effect to some degree.…”

Section: Implications For Modelling Ice Flow In Areas Of Large Topographic Reliefmentioning

confidence: 80%

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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“…The recommendations for sample collection based on our results also apply to subglacial bedrock locations that are targeted to test for past ice sheet collapse (e.g. Spector et al, 2019). In particular, sampled subglacial bedrock ridges on the downstream side of a nunatak may record past exposure indicative of a thinner-than-present ice sheet, but an equivalent subglacial ridge on the upstream side may record no such exposure.…”

Section: Implications For the Interpretation Of Past Ice Sheet Reconstructionsmentioning

confidence: 89%

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

et al. 2021

View full text Add to dashboard Cite

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 strong topographic relief that acts as an obstacle by modelling ice flow around and between idealised nunataks during periods of imposed ice sheet thinning. We find that, for realistic Antarctic conditions, a single nunatak can 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 is a delay in the time of bedrock exposure upstream relative to downstream of a nunatak summit. A nunatak elongated transversely to ice flow is able to increase ice retention and therefore impose steeper ice surface gradients, while efficient ice drainage through outlet glaciers produces gentler gradients. Such differences, however, are not typically captured by continent-wide ice sheet models due to their coarse grid resolutions. Their inability to capture site-specific surface elevation changes appears to be a key reason for the observed mismatches between the timing of ice-free conditions from cosmogenic exposure dating and model simulations. 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.

show abstract

Thickness of the divide and flank of the West Antarctic Ice Sheet through the last deglaciation

Cited by 18 publications

References 51 publications

Antarctic surface temperature and elevation during the Last Glacial Maximum

Antarctic surface temperature and elevation during the Last Glacial Maximum

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

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

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