Preliminary Results of Structural Analyses of an 85.6m Deep Ice Core Retrieved from Hoghetta Ice Dome in Northern Spitsbergen, Svalbard.

In 1987 an ice core to bedrock at a depth of 85.61m was recovered at Hoghetta ice dome in northern Spitsbergen. The ice temperature measured in the borehole was －11℃ at 10m depth and －9.4℃ at the bottom. Sudden transitions from large grains to small ones were observed in vertical thin sections of grains near the surface. These boundaries seem to indicate the discontinuity of the ice formation process which occurs periodically every year. Therefore, the boundaries can be used for identifying annual layers. From structural analyses of the ice cores at different 10 depths, it was found that grains of ice were inter-locked and have irregular boundary shapes in the middle depths. Some of them showed an elongated shape, the orientations of which seem to be perpendicular to the girdle plane derived from ice fabrics. These interlocking and elongated grains, along with characteristics of ice fabrics, can be related to a past specific stress condition in the ice body. We can speculate that the ice of the middle depth (approximately 20m - 65m) is remnant ice from a larger ice cap than at present, spread over northern Spitsbergen after the hypsithermal period