Abstract
AbstractAlthough the effects of snow during sea-ice growth have been investigated for sea ice which is thick enough to accommodate dry snow, those for thin sea ice have not been paid much attention due to the difficulty in observing them. Observations are complicated by the presence of slush and its subsequent freeze-up, and the surface heat budget might be sensitive to the additional ice thickness. An onsite short-term land fast sea-ice freeze-up experiment in the Saroma-ko Lagoon, Hokkaido, Japan was carried out to examine the effects of snowfall on the structure and surface heat budget of thin sea ice, based on observational results and a 1-D thermodynamic model. We found that snowfall contributes to the solidification of the surface slush layer, contributing ice thickness that is comparable to the snowfall amount and affecting the crystal texture significantly. On the other hand, the basal ice growth rate and turbulent heat flux were not significantly affected, being <3.1 × 10−8m s−1and 3 W m−2, respectively. This finding may validate the omission in past studies of snow effect in estimating ice production rates in polynyas and has implications about the reconstruction of growth history from sample analysis.
Highlights
The accumulation of snow on sea ice plays an important role in modifying the properties of sea ice in several ways
The weather conditions were relatively calm during both nights, a significant snowfall event occurred on the second night. This facilitated an examination of how snowfall can affect sea-ice structure, the subsequent ice growth and the turbulent heat flux
(2) Solidification of a surface slush layer during the freeze-up process has no significant effect on the subsequent ice growth and the turbulent heat flux
Summary
The accumulation of snow on sea ice plays an important role in modifying the properties of sea ice in several ways. With respect to sea-ice growth and the surface heat budget, the thermal insulation effect and process of snow-ice formation have mainly been investigated for sea ice that is thick enough to accumulate snow as a dry layer on top The effect on the freeze-up process of thin sea ice, complicated by the formation of slush containing sea water exposed to the air, is not fully understood due to the lack of observations. Thin sea-ice surface can potentially affect the production rate and subsequent crystal alignment through the seeding effect which induces crystallization (Martin, 1981; Gow, 1986; Weeks and Ackley, 1986; Svensson and Omstedt, 1994). Traditionally the effect of snow has been omitted when estimating the sea-ice production rate in polynyas (e.g. Pease, 1987; Martin and others, 1998; Tamura and others, 2008), this decision seems to have been for simplicity rather than based on observational facts and can give rise to large uncertainty in the computation (Spreen and Kern, 2017)
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