Flow and mixing near a glacier tongue: a pilot study

Abstract

A glacier tongue floating in the coastal ocean presents a significant obstacle to the local flow and so influences oceanic mixing and transport processes. Here acoustic Doppler current profiler and shear microstructure observations very near to a glacier tongue side-wall capture flow accelerations and associated mixing. Flow speeds reached around 40 cm s⁻¹, twice that of the ambient tidal flow amplitude, and generated vertical velocity shear squared as large as 10^−5 s⁻². During the time of maximum flow, turbulent energy dissipation rates reached 10^−5 m² s⁻³, around three decades greater than local background levels. This is in keeping with estimates of the gradient Richardson Number which dropped to ~1 during maximum flow. Associated vertical diffusivities estimated from the shear microstructure results were substantial, reflecting the influence of the glacier on velocity gradients.