Properties of sea ice and overlying snow in the Southern Sea of Okhotsk

Abstract

The general properties of sea ice and overlying snow in the southern Sea of Okhotsk were examined during early February of 2003 to 2005 with the P/V “Soya”. Thin section analysis of crystal structure revealed that frazil ice (48% of total core length) was more prevalent than columnar ice (39%) and that stratigraphic layering was prominent with a mean layer thickness of 12 cm, indicating that dynamic processes are essential to ice growth. The mean thickness of ice blocks and visual observations suggest that ridging dominates the deformation process above thicknesses of 30 to 40 cm. As for snow, it was found that faceted crystals and depth hoar are dominant (78%), as which is also common in the Antarctic sea ice, and is indicative of the strong vertical temperature gradients within the snow. Stable isotope measurements (δ18O) indicate that snow ice occupies 9% of total core length and that the mass fraction of meteoric ice accounts for 1 to 2% of total ice volume, which is lower than the Antarctic sea ice. Associated with this, the effective fractionation coefficient during the freezing of seawater was also derived. Snow ice was characterized by lower density, higher salinity, and nearly twice the gas content of ice of seawater origin. In addition, it is shown that the surface brine volume fraction and freeboard are well correlated with ice thickness, indicating some promise for remote sensing approaches to the estimation of ice thickness.