  Sea ice growth with lamellar microstructure containing brine channels has
been extensively investigated. However, the quantitative growth information of
sea ice remains lack due to the uncontrolled crystalline orientation in
previous investigations. For the first time, we in-situ observed the
unidirectional growth of lamellar sea ice with well-manipulated ice crystal
orientation and visualized tip undercooling of sea ice. A semi-empirical model
was proposed to quantitatively address the variation of tip undercooling with
growth velocity and salinity and compared with a very recent analytical model.
With the real-time observation, interesting phenomena of doublon tip in
cellular ice growth and growth direction shift of ice dendritic tip were
discovered for the first time, which are attributed to the complex solutal
diffusion and anisotropic interface kinetics in sea ice growth. The
quantitative experiment provides a clear micro scenario of sea ice growth, and
will promote relevant investigations of sea ice in terms of the theoretical
approach to describing the diffusion field around faceted ice dendritic tip.
