A Direct Estimate of Volume, Heat, and Freshwater Exchange Across the Greenland-Iceland-Faroe-Scotland Ridge

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The flow of warm salty water toward the Nordic Seas is of fundamental importance to the climate of central and northern Europe. In an effort to gain an improved quantitative assessment of these fluxes a program was started in 2008 to measure upper-ocean currents from the high-seas ferry Norröna, which operates out of the Faroes to Iceland and Denmark. The current measurements were made with an acoustic Doppler current profiler mounted in the Norröna's hull. Starting in fall of 2013 monthly deployments of Expendable BathyThermographs give comprehensive information on the temperature field. These velocity and temperature data can be combined to estimate mean volume and temperature fluxes (referenced to 0 °C) for the two sections. Archived hydrographic data give us the corresponding salt transport. Thanks to an array of 12 tall moorings across the Blosseville Basin that measured currents, temperature, and salinity net transport of volume, temperature, and salt between Iceland and Greenland can also be estimated. By combining the velocity data from these three sections the strength of the Nordic Seas branch of the meridional overturning circulation is estimated to be 7.7 ± 0.8 Sv where 1 Sv = 106 m3/s. Imposing the constraint of zero net volume and salt flux, the corresponding heat and freshwater fluxes are estimated to be 264 ± 27 TW (1 TW = 1012 W) and −0.104 ± 0.01 Sv, respectively. The uncertainties in heat and freshwater fluxes are largely governed by volume fluxes. The Norröna program is ongoing.

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Journal of Geophysical Research: Oceans