Monitoring the flow of Atlantic water through the Faroe-Shetland Channel

This report presents results from an experiment, carried out in 2011-2012 within the EU-THOR project to investigate whether future monitoring of the Atlantic water transport through the Faroe-Shetland Channel might be more efficiently achieved on another section than the traditional Munken-Fair Isle section. The new section is less affected by meso-scale activity and narrower, allowing better horizontal resolution of the mooring array, but the experiment revealed that moving to the new section involved other drawbacks. The experiment also confirmed an earlier conjecture that data from satellite altimetry might provide better estimates of transport variations than estimates based on in situ measurements, solely. Previous efforts to determine the average volume transport of Atlantic water through the channel and its variations have been hampered by lack of information on the thickness variations of the Atlantic layer. Re-evaluating the historical data set, we find that the transport estimates are not significantly affected by assuming that the lower boundary of the Atlantic layer is fixed, equal to the average 5°C-isotherm. Based on the conclusions of this report, we recommend that future in situ monitoring in the channel is re-focused.