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Abstract
Abstract. One-dimensional simulations of firn evolution neglect horizontal advection from ice flow, which transports the firn column across climate gradients as it is buried by accumulation. Using a suite of model runs, we demonstrate the impacts of horizontal advection on the development of firn density, temperature, and the stratigraphy of melt features through the Greenland ice sheet percolation zone. The simulations isolate processes in synthetic runs and investigate four specific transects and an ice core site. Relative to one-dimensional simulations, the horizontal advection process tends to increase the pore close-off depth, reduce the heat content, and decrease the frequency of melt features with depth by emplacing firn sourced from higher locations under increasingly warm and melt-affected surface conditions. Preservation of the advected pore space and cold content is strongly dependent upon the depth of meltwater infiltration. Horizontal ice flow interacts with topography, climate gradients, and meltwater infiltration to influence the evolution of the firn column structure; the interaction between these variables modulates the impact of horizontal advection on firn at locations around Greenland. Pore close-off and firn temperature are mainly impacted in the lowermost 20–30 km of the percolation zone, which may be relevant to migration of the lower percolation zone. Relatively high in the percolation zone, however, the stratigraphy of melt features can have an advection-derived component that should not be conflated with changing climate.
Highlights
Summer melting of bare ice, epitomized by stream networks and moulins, represents a relatively small portion of the Greenland ice sheet (GrIS) periphery since about 90 % of the ice sheet’s area is a perennially snow-covered accumulation zone (e.g., Ettema et al, 2009)
Surface speeds approaching the upper limit of what may be expected in the GrIS percolation zone generate a firn column with air content that can differ from 1D simulations by 80 %
Elevated horizontal ice flow in the percolation zone compared to ice divides results in a firn column that is not always well represented by 1D models for time-evolving density and temperature
Summary
Summer melting of bare ice, epitomized by stream networks and moulins, represents a relatively small portion of the Greenland ice sheet (GrIS) periphery since about 90 % of the ice sheet’s area is a perennially snow-covered accumulation zone (e.g., Ettema et al, 2009). Melting of the accumulation zone (i.e., the percolation zone) is an increasingly important aspect of the ice sheet, and so too are the glaciological processes governing the snow and firn interactions with surface climate. Many aspects of the processes governing firn’s structural and thermal evolution and whether meltwater is retained remain unclear. While current model fidelity prevents confident constraint on the amount of melt retained in the percolation zone, existing estimates are that 40 %–50 % of the meltwater generated
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