We describe hydrographic sections carried out by two autonomous undersea vehicles in the Labrador Sea, as part of the ASOF (Arctic-Subarctic Ocean Flux) program. The first such exploration began offshore of Nuuk, Greenland on 2 October 2003, in a program directed at high-latitude ocean climate change. Two Seagliders were launched at the 1000m isobath in the Labrador Sea. During the subsequent 4 months the gliders traversed about 4000 km of sections, making 1550 conductivity-temperature-depth profiles. Observations of temperature, salinity, dissolved oxygen, fluorescence and two-channel particle scattering were made along the sawtooth paths, with average horizontal resolution of 3 km. The vehicle’s known flight characteristics make it possible also to measure vertically averaged horizontal velocity and fine-scale vertical velocity, giving estimates of horizontal circulation and vertical convection/internal waves. Control and data transmission occurs through the Iridium satellite system, during the three-times daily surfacing of the vehicle, and has been successful in one of the stormiest seas on Earth. Meridional sections have been carried out along 55W and 58W, crossing the central Labrador Sea gyre to the Labrador continental shelf. The shape of the Labrador Sea gyre has been determined along these lines, contrasting the narrow boundary currents and broad, multi-path limb of the gyre in the northwestern Labrador Sea. Interior fronts have been found, in which the mixed-layer changes depth by 50% in 3 km or less. Strong anticylonic eddies have been profiled, some of which carry a ‘top-hat’ of low-salinity shelf water out to the central Sea. The transport of fresh-water in the surface layer of the Labrador Sea, its communication with the low-salinity shallow circulation on the continental shelves, and its engulfment into deep-waters by deep wintertime convection are objects of interest. Several traverses across the strong boundary currents on both Labrador and Greenland continental rises, were carried out.

Fresh-water flux from the Arctic into the Atlantic, and local precipitation and run-off, produce a buoyant upper ocean resistant to deep convection. The geography of this dynamic height anomaly is crucial to representation of the meridional overturning process in climate models, yet it is very poorly known. The high spatial resolution of the Seaglider is well suited to mapping this signal.