Observing depth-averaged and surficial currents across the North Pacific

An experimental hydrographic cruise which combined horizontal electromagnetic profiling with currents estimated from the ship´s set to produce high-resolution horizontal profiles of both surficial and depth-averaged oceanic flows is described. This experimental approach produced two independent data sets containing information about surface-layer currents directed across the track of the towing vessel. Combining these two data sets from the North Pacific section showed that depth-averaged meridional flows were weak everywhere across the subpolar gyre. Intercomparison with simultaneous measurements of geostrophic surface current showed that summertime surface flows were not only mostly baroclinic, but predominantly ageostrophic, exhibiting typical amplitudes of 0.25 ms^-1 and wavelengths of hundreds of kilometers