28 Oct 2022
 | 28 Oct 2022

A model of the weathering crust and microbial activity on an ice-sheet surface

Tilly Woods and Ian J. Hewitt

Abstract. Shortwave radiation penetrating beneath an ice-sheet surface can cause internal melting and the formation of a near-surface porous layer known as the weathering crust, a dynamic hydrological system that provides home to impurities and microbial life. We develop a mathematical model, incorporating thermodynamics and population dynamics, for the evolution of such layers. The model accounts for conservation of mass and energy, for internal and surface-absorbed radiation, and for logistic growth of a microbial species mediated by nutrients that are sourced from the melting ice. It also accounts for potential melt-albedo and microbe-albedo feedbacks, through the dependence of the absorption coefficient on the porosity or microbial concentration. We investigate one-dimensional steadily melting solutions of the model, which give rise to predictions for the weathering crust depth, water content, melt rate, and microbial abundance, depending on a number of parameters. In particular, we examine how these quantities depend on the forcing energy fluxes, finding that the relative amounts of shortwave (surface-penetrating) radiation and other heat fluxes are particularly important in determining the structure of the weathering crust. The results explain why weathering crusts form and disappear under different forcing conditions, and suggest a range of possible changes in behaviour in response to climate change.

Tilly Woods and Ian J. Hewitt

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1086', Andrew Tedstone, 15 Nov 2022
    • AC1: 'Reply on RC1', Tilly Woods, 28 Nov 2022
  • CC1: 'Comment on egusphere-2022-1086', Martyn Tranter, 28 Nov 2022
    • AC2: 'Reply on CC1', Tilly Woods, 28 Nov 2022
  • RC2: 'Comment on egusphere-2022-1086', Sammie Buzzard, 23 Dec 2022
    • AC3: 'Reply on RC2', Tilly Woods, 04 Jan 2023

Tilly Woods and Ian J. Hewitt

Model code and software

Weathering crust and microbial activity code Tilly Woods

Tilly Woods and Ian J. Hewitt


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Short summary
Solar radiation causes melting at and just below the surface of the Greenland ice sheet, forming a porous surface layer known as the weathering crust. The weathering crust is home to many microbes, and the growth of these microbes is linked to the melting of the weathering crust and vice versa. We use a mathematical model to investigate what controls the size and structure of the weathering crust and the number of microbes within in, and its sensitivity to climate change.