Absolute flow field estimation for the Nordic seas from combined gravimetric, altimetric, and in situ data

In the Nordic seas, we combine a computation of absolute surface current flow derived from geodetic data with in situ historical hydrographic data to estimate the absolute volume, heat, and salt transports as a function of depth. Our mean dynamic topography (MDT) is calculated from marine, airborne and satellite gravimetry, combined with satellite altimetry, using a new algorithm called the iterative combination method (ICM). Residual noise in the gravimetric geoid is the limit on MDT resolution and is suppressed using a Gaussian filter with a width at half-peak amplitude of 59 km. Detailed and coherent flow paths for surface geostrophic currents are clearly identified. ICM MDT was used as fixed boundary condition to transform historical hydrography into absolute estimates of volume, heat, and salt transport, replacing the assumption of an isobaric surface at a predetermined depth. For the inflow of Atlantic Water (potential temperature Theta > 6 degrees C) through the Faroe-Shetland Channel into the Nordic seas, we obtain time-averaged fluxes between 1993 and 1996 of 3.5 Sv (volume), 121 TW (heat), and 124 x 10(6) kg s(-1) (salt), very close to reported observations from acoustic Doppler current profiler moorings and conductivity-temperature-depth data. For the Svinoy section, we obtain a northward transport of Atlantic Water (S > 35.0, T > 5.0 degrees C) of 3.9 Sv in the eastern branch of the Norwegian Atlantic Current comparable with reported measurements of 4.2 Sv. Similarly good agreement is found for the Hornbanki and Iceland-Faroe Ridge sections and for monitoring Atlantic Water outflow across the Barents Sea Opening to the Arctic shelf.