Successful Mooring Recovery in the Subtropical Atlantic

In April 2019 a scientific crew on research vessel Poseidon recovered successfully a mooring that was deployed one year ago. In May 2018 a TRR 181 research team supervised by Dr. Maren Walter from University Bremen explored the dispersion of Tidal Energy along a path from the southern Azores.

Weekly report by Janna Köhler and the scientific party of POS533/2:

The Poseidon cruise POS533/2 is part of the TRR 181, an interdisciplinary research program of the Deutsche Forschungsgemeinschaft (DFG). POS533-2 is the third expedition to the area south of the Azores within the TRR181 after last years’ POS523 in 2018 and POS516 in 2017. Tidal forcing excites so-called internal tides at steep topography such as seamounts and the continental shelf. These internal tides have the form of underwater waves that may travel hundreds of kilometers across ocean basins. Along their paths, the waves lose their energy by a range of processes and interactions, but the how and where is mostly unknown.

Our project has the aim of better understanding the fluxes and dissipation of this tidal energy in the ocean interior to improve the representation of these processes in climate models.

Goal of the cruise

South of the Azores seamounts generate very energetic internal tides that form a so-called internal tide beam which radiates energy southwards towards the Cap Verde Islands. During POS516 and POS523 we conducted a spacial survey to better understand the fluxes and dissipation of the internal tides. A mooring measuring time series of temperature and current velocities was redeployed during POS523 in May 2018. Its data will be used to study the temporal variability in the energy of the internal tides. The retrieval of this mooring is the main goal of this cruise.

Mooring recovery process

At noon of the 25th we started our 4-day trip to the mooring position which gave us enough time to prepare everything for the mooring recovery. On our way to the mooring, we carried out a 2000m Conductivity/Temperature/Depth- (CTD) Profile to take water samples that will be used for the calibration of salinity measurements.

On the morning of Friday 29th March, we reached the mooring position and successfully recovered our mooring. Thanks to the great work of the captain and crew of the Poseidon, all our instruments
could be retrieved in good condition, having been in the ocean for ten months since May last year.

Heading home

Right after the mooring recovery and a shallow CTD cast for sensor calibration, we set course towards Ponta Delgada (Azores) where we will, despite the best effort of Captain Guenther and his
crew, only arrive on Monday 1st of April, one day later than originally planned due to the late start in Las Palmas and unfavorable wind and wave conditions.


Interview with Janna Köhler and Jonas Löb in May 2018

During the research cruise in May 2018 the research team deployed the mooring. Watch here an interview with two scientists from University Bremen about the recovery process.