The role of Langmuir circulation in suspension freezing

Abstract

In November 2004 we used an acoustic Doppler velocimeter (ADV) to measure the three components of velocity in Langmuir circulation (LC cells when frazil was forming in a lake. LC circulation was indicated by windrows of slush ice on the water surface. We also collected samples of lake water, ice interstitial water and ice to determine their sediment concentrations. The ADV record showed rotating currents in the cross-wind/vertical plane indicative of LC. Downward-directed velocities were large enough to entrain frazil into the water column for 27% of the 97 min observation time at the ADV location. Sediment concentrations in the ice and interstitial water samples were greater than concentrations in water-column samples collected in upwelling zones of LC cells. We conclude that suspension freezing was forming particle-laden ice as frazil trapped below LC convergence zones grew in downwelled, supercooled water. The rotating roll vortices of Langmuir circulation play an important role in forming sediment-laden ice.