Ocean current direction measurements through the Canadian archipelago have required development of a strategy that uses specialised instrumentation to cope with the small horizontal component of the earth's magnetic field in this region. Subsurface instrumented moorings collecting bihourly data through yearlong deployments, use precision heading reference systems to measure the orientation of Acoustic Doppler Current Profilers mounted in streamlined buoyancy packages. Current directions are then corrected for the significant fluctuations in magnetic declination occurring near the magnetic pole, using data from a nearby geomagnetic observatory. Concurrent observations of current speed and direction from independent moored measurement systems are shown to be in good agreement.
Current measurements near the magnetic poles require special strategies and instrumentation to adequately resolve direction. This is because of the small horizontal component of the earth's magnetic field there that renders compasses in commercially available current meters ineffective, and also because of the requirement to correct for the variation in magnetic declination that occurs there. (Magnetic declination is the angle between true north and magnetic north.) A third difficulty is that the weak horizontal field increases the potential for contamination of direction measurements by magnetic mooring hardware. A field program to quantify heat and salt fluxes through Barrow Strait was started in 1998. Barrow Strait is one of three main connections between the Arctic Ocean and the Northwest Atlantic. The program required the development of a methodology to collect yearlong current rate and direction data only 700 km from the North Magnetic Pole (see Fig. 1), where the dip angle (the angle that the magnetic field vector makes with the horizontal) is 88.2°. Here, the force imposed by the horizontal component of the magnetic field is insufficient to reliably overcome the friction in the pivot of a conventional compass.
