Seagliders have proved an effective low-cost means to survey upper ocean internal structure in a severe environment. The ASOF Labrador Sea missions described here were the first experience for this technology in an environment where the ability to respond to vehicle malfunctions was severely limited by its remoteness and severe weather and sea conditions. The experience of losing the first two gliders as their communications became more and more intermittent motivated considerable changes in Seaglider software, including the ability to download entirely new versions of the glider operating code and reboot to it remotely. Despite difficulties and hardware losses, the data collection could not have been obtained by traditional shipboard means without extraordinary expense. The Labrador Sea experience validated the model of sending a small team to a remote location, basing operations on land, while using small boats on day trips to launch and recover gliders. We also departed from that model to use large research vessels when they were made available on an ancillary basis. The launches from R/V Knorr were the first Seaglider operations from a conventional oceanographic vessel.

We learned that to sustain effective glider measurements in the Labrador Sea, vehicles capable of year-long missions and ones less hampered by strong currents would be helpful. We look to the extended range version of Seaglider and to Deepglider to provide these advantages in the future. The problem of making synoptic measurements with a slowly moving platform remains and appears addressable by the use of more vehicles (than 2), repeating transects more often.

Acknowledgements Glider operations in the Labrador Sea benefited greatly from the support of the Greenland Institute of Natural Resources, Nuuk, our U.W. colleagues C. Lee and J. Gobat and their research group, the officers and crew of R/V Knorr and CCGS Hudson, and N. Bogue, T. Swanson, J. Bennett, and W. Fredericks. The work was supported by the US Office of Naval Research under grant N00014-02-1-0791 and the US National Oceanic and Atmospheric Administration Arctic Research Office. Work on the Iceland-Faroe Ridge is supported by the National Science Foundation through grant OCE-0550584. We thank the Faroese Fisheries Laboratory, Drs. B. Hansen and H. Hatun, and the Faroese Coast Guard for their considerable assistance.

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