ИСТИНА

A mooring equipped with two acoustic Doppler current profilers (ADCP) and a sediment trap was deployed in September 2016 in Hudson Bay at 59° 58.156’ N 91° 57.144’ W (~190 km north-east from the port of Churchill). The backscatter intensity and vertical velocity time series from the mooring ADCPs showed a pattern typical for the zooplankton diel vertical migration (DVM) under sea ice during winter. To correct for beam geometry, we derived volume backscatter strength from echo intensity. Actograms were built for the volume backscatter strength, vertical velocity and modelled lunar light. An upward looking ADCP was capable to record the ice thickness and periods of open water above the mooring. The sediment trap captured different types of zooplankton that allow identifying the scatters involved in DVM. From the acquired data we observed the interaction of vertical migration with lunar light, tides, water and sea ice dynamics. The presented data constitutes a first-ever observed presence of DVM in Hudson Bay during winter.