Exploring the conditions conducive to convection within the Greenland Ice Sheet

Enigmatic large plume-like features disrupt the radiostratigraphy within the Greenland Ice Sheet. Here we use the ASPECT geodynamics modelling package to test the hypothesis that convection is a viable mechanism for the formation of the large (>1/3 ice thickness) englacial plume-like features observed in north Greenland, provided that there is a modest initial temperature perturbation. Both greater horizontal shear and snow accumulation impede formation of convection plumes, while low shear and softer ice encourages them. These results potentially explain the dearth of larger basal plumes in the younger and higher-accumulation southern ice sheet. We leverage this apparent convection mechanism to place bounds on ice rheology, which suggests that – for parts of north Greenland – effective ice viscosity may span ∼2×1012–3×10 14 Pa s, or around an order of magnitude lower than commonly assumed. Softer ice there implies reduced basal slip compared to standard models. Isolating if this effective viscosity range is impacted by additional processes (like basal freeze on and travelling slippery patches) and implementing a softer basal ice rheology in numerical models may help reduce uncertainty in projections of future ice-sheet mass balance.