Meltwater retention in a transect across the Greenland ice sheet

Meltwater retention by freezing is a highly climate-sensitive term in the mass budget since the cold content is directly controlled by winter climate, which is expected to change most in an anthropogenic-driven climate change. Meltwater released at the surface percolates into dry snow in a pattern with alternating horizontal and vertical water-flow directions, where the processes of pore refreezing (RF) (vertical flow) and superimposed ice (SI) formation (horizontal flow) occur. The flow cannot be forecasted and quantified when water first enters cold, dry snow. However, because the two processes are driven by different physical mechanisms, their potential magnitude can be estimated, which has been done in a transect at 66° N. Results show that SI declines from west to east and inversely correlates with accumulation. From the total retention capacity, theoretical lowest-runoff lines were determined at ∼1400ma.s.l. in the west and ∼1600ma.s.l. in the east. Since the SI potential is high in most places and the warming from SI formation predominately occurs near to the surface, it is argued that winter cooling effectively recharges the cold content of the snow/firn/ice pack, preventing the development of isothermal conditions and subsequent runoff. However, SI formation declines over time, so an extension of the melting season could result in deeper percolation beyond the SI layer.