Estimation of the age of ice hummocks in the freezing seas

Abstract

A method of estimating the ice ridge age proposed in the 1990s was analyzed and some disadvantages of this method were shown. Analysis of the ice thickness distribution in the ice ridges demonstrated that in many cases the average value of the thickness used in the above mentioned method did not correspond to the thickness of an ice floe of which the ice blocks were formed. The ice floe thickness is characterized by the modal value of the ice thicknesses. After the ice ridge has been formed the ice block thickness in its above-water part does not change while the thickness of the ice floe on which the ice ridge is located continues to increase. Our study has shown that the difference between thickness of the plane ice and the modal value of the ice block thickness may be used as a characteristic of the ice growth for the period of the ice ridge existence. This period can be determined by one of the calculation formulas at the known initial and final ice thickness. Calculation by formula of the ice growth thickness make possible to derive the date of ice ridge formation based on the average air temperatures. The updated method of estimating the time of ice ridge formation can be used for the ice-covered seas. Analysis of the estimated ice ridge ages showed a significant dependence of thickness of the minimal consolidated layer on the time of the ice ridge formation. A comparative analysis of (the) ages of ice ridges and the flexural strength of ice samples made it possible to determine important tendency - the increased ice strength in ice ridges of early formation. This allows us in further studies to derive a formula of relationship between an ice ridge age and a strength of its ice. In some cases the ice strength measurement in ice ridges can be replaced by a less laborious estimating of strength basing on data of the age.