Position: 82° 54.52' N, 12° 56.3' W, temperature - 3 °C, air pressure 1025 hPa, wind 12 knots from the N. Ice drift 0.15 knot towards S. A glorious day. Felt a shock at 0137 GMT and thought it may have been an earthquake from the Lena Trough below. However, both NORSAR, Univ. of Bergen and GEUS did not see any events recorded on the Svalbard stations or at St. Nord. The shock could have been related to the start of a pressure ridge about 35 meter in front of the hovercraft. Made CTD cast to 1000 m depth. Both ARGOS tracker buoys report good positions - batteries checked 12.4 and 11.9 volt.