The diurnal evolution of oceanic boundary layer beneath early-frozen landfast ice in Prydz Bay, East Antarctica

Abstract. The ice–ocean boundary layer parameters are one of the main drivers of sea ice mass balance in the Polar Regions. To investigate the oceanic contribution to the landfast ice evolution, an integrated ocean observation system, including Acoustic Doppler Velocimeter, COMPACT-CTD, and Sea Ice Mass Balance Array, was deployed near Zhongshan Station in Prydz Bay, East Antarctica. The minute-resolution of ocean temperature, salinity, density, current, and heat flux from 16 to 23 April, 2021 were obtained and analysed. The results showed that ocean temperature experienced a jump increase, from -1.59±0.03 °C during 16–19 April to -1.47±0.07 °C during 20–23 April, which may relate to the tide transform from semi-diurnal to diurnal. Ocean salinity and density showed a gradual trend increasing by 0.013 psu day^-1 and 0.009 kg m^-3 day^-1, respectively, related to the salt rejection of ice bottom freezing. The mean ocean velocity was 3.13±1.63 cm s^-1 and 34 % of the current directions accounted to the northwest. Oceanic heat flux was estimated by the bulk parameterization method and residual energy method, which were 32.26±18.07 W m^-2 and 34.95±17.52 W m^-2, averaged for the study period respectively. Oceanic heat flux showed a large increase during 20–23 April, which shut down ice growth and resulted in 2 cm melting at the ice bottom. The high frequency of ocean observations allows us to deeply investigate diurnal changes of oceanic regimes and understand their influences on sea ice evolution.