Tide-induced perturbations of glacier velocities

Recent observations showing substantial diurnal changes in velocities of glaciers flowing into the ocean, measured at locations far inland of glacier grounding lines, add fuel to the ongoing debate concerning the ability of glaciers to transmit longitudinal-stress perturbations over large distances. Resolution of this debate has major implications for the prediction of glacier mass balance, because it determines how rapidly a glacier can respond dynamically to changes such as weakening or removal of an ice shelf. Current IPCC assessment of sea-level rise takes little account of such changes, on the assumption that dynamic responses would be too slow to have any appreciable effect on ice discharge fluxes. However, this assumption must be questioned in view of observations showing massive increases in glacier velocities following removal of parts of the Larsen Ice Shelf, Antarctica, and of others showing diurnal velocity changes apparently linked to the tides.