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Use of an autonomous underwater vehicle (AUV) to obtain environmental observations beneath coastal sea ice offshore of Barrow, AK, is described. This study is motivated by the desire to obtain cross-shore hydrographic transects (temperature, salinity, and velocity versus depth) that would provide estimates of the transport of relatively dense, salty water from the Chukchi Sea to the Arctic Ocean in winter. Although person-portable AUVs are well suited to the task, it was recognized that achieving the science goals would require increasing the range of acoustic navigation and communication as well as developing a robust approach to through ice deployment and recovery. These needs drove three modifications to the AUV: 1) incorporation of a lower frequency (10 kHz) transponder and associated hardware for navigation and communication; 2) addition of special-purpose sensors and hard- ware in a hull extension module; and 3) development of a homing algorithm utilizing Ultrashort Base Line acoustics. In March 2010, eight days of field work offshore of Barrow provided successful demonstration of the system. A total of 14 km of track lines be- neath a coastal ice floe were obtained from four missions, each successfully terminated by net-capture recovery.