Basal freeze-on generates complex ice-sheet stratigraphy

G J.-M C Leysinger Vieli,C Martín,R C A Hindmarsh,M P Lüthi

doi:10.1038/s41467-018-07083-3

G J.-M C Leysinger Vieli, C Martín + Show 2 more

Open Access

https://doi.org/10.1038/s41467-018-07083-3

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Abstract

Large, plume-like internal ice-layer-structures have been observed in radar images from both Antarctica and Greenland, rising from the ice-sheet base to up to half of the ice thickness. Their origins are not yet understood. Here, we simulate their genesis by basal freeze-on using numerical ice-flow modelling and analyse the transient evolution of the emerging ice-plume and the surrounding ice-layer structure as a function of both freeze-on rate and ice flux. We find good agreement between radar observations, modelled ice-plume geometry and internal layer structure, and further show that plume height relates primarily to ice-flux and only secondarily to freeze-on. An in-depth analysis, performed for Northern Greenland of observed spatial plume distribution related to ice flow, basal topography and water availability supports our findings regarding ice flux and suggests freeze-on is controlled by ascending subglacial water flow. Our results imply that widespread basal freeze-on strongly affects ice stratigraphy and consequently ice-core interpretations.

Highlights

Large, plume-like internal ice-layer-structures have been observed in radar images from both Antarctica and Greenland, rising from the ice-sheet base to up to half of the ice thickness
In Greenland the relief of the subglacial topography is less pronounced than in Antarctica, we find that plume-like structures are predominantly located on the flanks of the main subglacial basin in regions of moderate ice flow and surface slope (Fig. 1b–d)
To verify the relationship with a rising bed, we define an index for freeze-on (Φ) as a purely geometrical quantity (see Methods section 'Basal freeze-on index’ Eq (25)) that accounts for the effect of the bed incline on freeze-on triggered by PiDMP

Summary

Introduction

Plume-like internal ice-layer-structures have been observed in radar images from both Antarctica and Greenland, rising from the ice-sheet base to up to half of the ice thickness. What had been identified as mountains in previous RES profiles[7] has been recognised to be large-scale plume-like internal ice-layer structures, observed for example in large numbers in the Gamburtsev mountains, East Antarctica, as well as in Northern Greenland[8,9] (Fig. 1a). Such ice structures extend from the bed to up to as much as half of the ice thickness, and horizontally over several ice thicknesses (Supplementary Fig. 1); the formation mechanism remains unclear[10]. Water will freeze onto the base with the released latent heat keeping the temperature of the uphill flowing water close to its melting temperature

Methods

Results

Conclusion