Access to the Sea Fund

Glider Observation of the Western Arctic Boundary Current

Donglai Gong, Robert S. Pickart and Lee E. Frietag

The Alaska Coastal Current (ACC) in the Chukchi Sea and the Beaufort Shelfbreak Jet (BSJ) in the Beaufort Sea are two segments of an extended coastal boundary current that transports a large fraction of the heat and freshwater from the Pacific ocean into the Arctic ocean. The ACC and BSJ join at the mouth of Barrow Canyon. Previous observations have revealed large along-shelf hydrographic and flow variability on distance scales of over 100 km inside Barrow Canyon and along the Alaskan Beaufort shelfbreak. Some of this variability can be attributed to the exchange of heat and salt between the boundary current and the deep basin. Eddy formation in the boundary current due to barotropic and baroclinic instabilities, as well as shelfbreak upwelling driven by easterly winds, are two of the physical processes that can efficiently facilitate exchange at the shelfbreak and affect the ventilation of the upper halocline. Characterizing the along-shelf variability with sub-mesoscale resolution (~1 km) greatly would aid our understanding of how eddies and winds affect cross-shelfbreak exchange of heat and salt. To date, there has been no high resolution along-shelf hydrographic measurements of the ACC/BSJ boundary current with submesoscale resolution (~1 km).

With Access to the Sea’s support, we plan to use a Slocum glider, equipped with CTD and bio- optical sensors, to study the along-flow hydrographic structure of the ACC/BSJ boundary current system in the transition region immediately upstream and downstream of the mouth of Barrow Canyon. High resolution profiling data from the glider in the upper water column would enable us to measure the differing along-shelf evolution of the winter and summer Pacific water masses and characterize the effect of eddies and winds on the boundary current. The study will leverage logistics support already in place for a funded mooring cruise (Chief Sci.: Robert Pickart) for the Arctic Observing Network in the Beaufort Sea in October 2012.

This study also has a technology development/engineering component. The boundary current in the western Arctic is active year round and plays an important role in the ventilation of the Arctic halocline during the partially ice covered spring and autumn. The present generation of autonomous sampling platforms, such as the Slocum glider, can only be deployed during the ice-free summer season mainly due to the need to obtain regular surface GPS fixes for navigation. The project’s engineering goal is to test a prototype long distance acoustic communication technology to be used for future under-ice glider/AUV navigation in the Arctic shelfbreak environment. A hydrophone will be installed on the glider to record acoustic signals transmitted by a shipboard transducer at distance of 10-100 km away. The research and engineering effort from this study will aid the development of future external proposals to undertake more extensive longer-term studies of the Arctic boundary current system using autonomous mobile platforms.

Last updated: June 21, 2012