Mixing, Water Transformation, and Melting Close to a Tidewater Glacier

Marine-terminating glacier fjords play a central role in the transport of oceanic heat toward ice sheets, regulating their melt. Mixing processes near glacial termini are key to this circulation but remain poorly understood. We present new summer measurements of circulation and mixing near a marine-terminating glacier with active sub-glacial discharge. 65% of the fjord's vertical overturning circulation is driven by the buoyant plume, however we newly report intense vertical and horizontal mixing in the plume's horizontal spreading phase, accounting for the remaining 35%. Buoyant plume theory supports 2%–5% of total glacial melt. Thus, most of the heat associated with vertical overturing short-circuits the glacial front. We find however that turbulence in the horizontal spreading phase redistributes the short-circuited heat back into the surface waters of the near-glacial zone. Our findings highlight the need for further research on the complex mixing processes that occur near the glacier terminus.