Temperature and salinity in the Bohai Sea landfast ice: Observations and modelling

Temperature and salinity are essential thermodynamic properties of sea ice. A 40-day long field campaign was carried out in winter 2020/2021 in the northern Bohai Sea in the landfast sea ice to investigate the seasonal sea ice temperature and salinity evolution. Ice thickness was measured routinely. A thermistor string was used to measure the ice temperature. Ice samples were collected for salinity by coring (S-co) and crumbing (S-cr) methods. The mean vertical values of Sco and Scr were 4.8-5.8 psu and 8.3-13.8 psu, respectively. In cold ice, S-co and S-cr were very close to each other. When ice temperature increased to -5 C-degrees, S-co and S-cr tended to differ from each other, and the difference was at largest at ice bottom. The brine volume fraction (BVF) ranged between 0.03 and 0.21 for S-co and 0.03 and 0.32 for S-cr. The growth of ice reached a maximum of 3.7 cm/day in very cold conditions, while the average growth rate was 0.8 cm/day comparable to other seasonally ice-covered seas. A numerical sea ice thermodynamic model was applied to simulate the ice thickness with particular attention to the effect of S-co and S-cr on the ice mass balance. The modeled overall ice growth rate was 0.7 cm/day and agreed well with the observations but during cold periods the simulation was biased down (1.1 cm/day); a possible reason is underestimation of the thermal conductivity in the model. The modeled ice thickness differed by 3 cm when using Sco and Scr as the input salinity profiles indicating that salinity has a minor impact on sea ice mass balance during mid-winter.