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Optimization of the Greenland‐Scotland Ridge inflow arrays (D2.8)

Larsen, Karin Margretha; Hansen, Bogi; Jónsson, Steingrímur; Macrander, Andreas; Berx, Barbara; Walicka, Kamila; Østerhus, Svein

Ocean warm and saline Atlantic water (AW) flows northward towards the Arctic. This water crosses the
Greenland‐Scotland Ridge in three inflow branches:

  •  the Iceland branch,
  •  the Faroe branch and
  •  the Shetland branch.

The first monitoring of these branches was obtained along standard hydrographic sections and in the 1990s these observations were complemented by – at that time the state‐of‐the‐art technology – Acoustic Doppler Current Profilers (ADCPs) that could measure ocean currents directly. For many years the ADCPs were the backbone in transport estimates of the inflowing AW, but in order to get reliable estimates, a high number of moorings were necessary which was costly both in consumables and man‐power. Alternative methods were therefore needed. The process to optimise the inflow arrays began several years ago by the integration of Satellite Altimetry data . Over the years, more data have been obtained at the inflow arrays, including new data types, and within Blue‐Action analyses have been performed utilizing the available data in order to optimise the monitoring of the inflow arrays both with respect to cost and in order to produce more accurate estimates of AW volume, heat and salt transports. Resulting from the work undertaken in Blue‐Action, the recommendations for future monitoring the three inflow branches are as follows:

  • Iceland branch: Combined observations from one or two ADCP moorings (including hydrographicobservations at intermediate depth) and four annual hydrographic surveys.
  • Faroe branch: Combined observations from satellite altimetry, one ADCP mooring, three PIES (Pressure Inverted Echo Sounders), one bottom temperature logger and at least three annual hydrographic surveys.
  •  Shetland branch: A combination of gridded geostrophic surface velocities from satellite altimetry, at least three annual hydrographic cruises along the section and continued ADCP deployments at key sites (such as in the Shetland slope current).

The Blue-Action project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 727852
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