topographically-steered pathways through the Chukchi Sea [3]-[5]; the eastern most branch passes along the Alaskan coast and is concentrated between Barrow, AK and the eastern flank of Barrow Canyon before entering the Arctic

Use of a REMUS-100 AUV to obtain hydrographic observations beneath coastal sea ice offshore of Barrow, Alaska is described. The work is motivated by the desire to obtain crossshore hydrographic transects that would provide estimates of the transport of relatively dense, salty water from the Chukchi Sea to the Arctic Ocean in winter. The horizontal scales (~10 km), maximum water depths (~100 m) and desired measurements (temperature, salinity and velocity vs. depth) in the study region match the capabilities of a small AUV such as the REMUS-100. 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) transducer and associated hardware for navigation and communication, 2) Addition of special-purpose sensors and hardware in a hull extension module, 3) Development of a homing algorithm utilizing an Ultra-Short Base Line (USBL) array in the AUV nose cap. 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 beneath a coastal ice floe were obtained from four missions, each successfully terminated by net-capture recovery.