Interfacial generation of internal waves and turbulent heat flux due to enhanced inertial motion for deformed sea-ice floe: Preliminary results from MOSAiC expedition

Sea-ice drift becomes most energetic at last moment in summer when refreezing is about to onset. Perennial ice floes, surviving over all seasons, tend to experience a number of deformation events over yearlong drift, with uneven distribution in thickness. Deformed ice floes protrude tall keels into water of ice-ocean boundary, and then stir it up. Consequently, combination of fast ice drift and deformation-experienced perennial ice could be a primary source of momentum/thermal energy for upper waters through propagation of internal waves. In this study, during MOSAiC expedition, we attempted to perform direct observation of wave generation in ice-ocean boundary layer underneath a drifting ice floe in the central Arctic Ocean. Time series of turbulent signals, represented by Reynolds stress <u'w'> and eddy heat flux <w'T'>, were obtained by an eddy covariance system (ECS), coupling a high-frequency (34 Hz) single-point current meter and a temperature sensor. Vertical/temporal properties of near-inertial waves were obtained by a downward-looking ADCP, collocated with ECS on the same ice floe. At same time, a triangle of high-precision GPS systems tracked ice movement to represent mean drift speed, rotation and deformation about the same floe seamlessly in time. Preliminary analyses of those combined data suggested that pronounced signals of inertial motion occurred in early September of 2020 as sheer ice keels dragged underlying waters, stratified by accumulation of melt water. It then allowed occurrence of near-inertial internal waves that tend to be trapped within the interfacial boundary layer, located within top 20 m. At the conference, we will present latest and quantitative knowledges from the MOSAiC expedition.