Exploring the conditions conducive to convection within the Greenland Ice Sheet

Abstract. Large plume-like features within the Greenland Ice Sheet disrupt radiostratigraphy and complicate the use of isochrones in reconstructions of past ice dynamics. Here we use numerical modelling 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. Greater horizontal shear and snow accumulation impede formation of convection plumes, while stable and softer ice encourages them. These results potentially explain the dearth of basal plumes in the younger and higher-accumulation southern ice sheet. Leveraging this mechanism to place bounds on ice rheology suggests that – for north Greenland – ice viscosity may be ~9–15 times lower than commonly assumed. Softer-than-assumed ice there implies significantly reduced basal sliding compared to standard models. Implementing a softer basal ice rheology in numerical models may help reduce uncertainty in projections of future ice-sheet mass balance.