| Summary: | The project Collaborative Research: Long-term observations in the Switchyard region of the Arctic Ocean as part of the Arctic Observing Network (NSF Award Numbers 1022475 and 1023529) is a continuation of the work of the AON project A Modular Approach to Building an Arctic Observing System for the IPY and Beyond in the Switchyard Region of the Arctic Ocean (NSF Award Numbers 0633878 and 0633885,) from April 2007 to March 2011 and Collaborative Research: Circulation in the freshwater switchyard of the Arctic Ocean (NSF Award Numbers 0230238 and 0230427) from Jan 2003 December 2007. These continued awards support a further three years (2011 - 2013) of ocean observations in the 'Switchyard region', the area north of Ellesmere Island, Canada, and Greenland, where water flows south out of the Arctic Ocean via Fram and Nares straits. The 'Switchyard' observing effort is part of the NSF Arctic Observing Network (AON), which supports long-term, science-driven observing that enables research into understanding rapid environmental system change in the Arctic. AON is a component of the broader Study of Environmental Arctic Change (SEARCH). The key elements of the 'Switchyard' observations are: (1) An aircraft-based section using a CTD-O/rosette system between Alert and the North Pole of hydrographic properties and a set of tracers/carbon system variables aimed at resolving the relative age structure via CFC, SF6 and tritium/helium-3 measurements, and freshwater components via oxygen-18, salinity and nutrient measurements in the upper water column (2) An aircraft-based hydrography/tracer survey of the Lincoln Sea aimed at capturing changes in the regional freshwater routing and the front between the boundary current and the transpolar drift passing through the 'Switchyard' region 
 (3) A mooring array across the shelf slope just west of Nares Strait aimed at capturing the structure and transport of the water masses coming around the Canada Basin on their way to Nares and Fram straits. Successful completion of the award will extend the 'Switchyard' observational record to 10 years, which will allow researchers to improve the understanding of the following: (1) Water mass characteristics and their effect on stratification, diapycnal heat fluxes, and transport of heat and salt (2) Freshwater inventories (including that stored in form of sea ice) (3) Freshwater release to the North Atlantic Ocean (4) Heat budget of the upper water layers and its interplay with the sea ice cover (5) Sea ice circulation and thickness distribution (6) Future circulation patterns Broader Impacts: The Arctic is undergoing a transition into a warmer world, and the data obtained in the 'Switchyard' region will provide early indications of how the Arctic environmental system is responding to anthropogenic forcing. NSF Program(s): Arctic Observing Network (AON) Sponsors: - University of Washington, 4333 Brooklyn Ave NE, Seattle, WA 98195 206/543-4043 
 - Columbia University, 2960 Broadway, New York, NY 10027 212/854-6851
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