Sampling gases from seawater

Poseidon cruise 527 is our second visit to Goldeneye to establish the environmental baseline conditions of the area. Contrary to last year’s visit, the weather this time has been on our side and we have managed to collect almost 3 times more samples as last year.
We used a standard 12 Niskin bottles CTD rosette to collect samples for dissolved gases (oxygen and CO₂), nutrients and organic matter in the water column at 12 different depths. The CTD frame is deployed by a winch to the bottom of the water column (as close to the seafloor as possible (around 1 m above) and during the up-cast the bottles are closed at chosen depths.

With the CTD rosette we were also able to obtain full-depth profiles of water column parameters like salinity, temperature, oxygen and fluorescence (chlorophyll). Together the samples and CTD sensor measurements define some of the key parameters for the assessment of the major biogeochemical processes within the water column near Goldeneye.

CTD rosette ready for action

On the CTD casts we also deployed pH and pCO₂ optode sensors, and on some of the CTD casts we deployed phosphate and pH lab on chip sensors. These deployments were successful and allowed us to gain insights into the sensor operations. The sensor data will be compared to the discretely sampled nutrient and carbonate chemistry data (following sample analysis back in the laboratory at GEOMAR).

Water samples for gases, nutrients and organic matter

In shelf seas such as the North Sea these parameters are strongly affected by natural daily/seasonal environmental variations, but also by anthropogenic disturbances. In the framework of the STEMM-CCS project, it is crucial to detect and discriminate variations caused by potential leakages at CCS sites from variations in natural background signals. Our goal is to determine an effective environmental baseline in order to provide the data needed to define measurement strategies for a controlled sub-seabed CO₂ release experiment, which is planned for May 2019.

The collection of samples could not have been possible without the great support from our Captain and crew on board of the Poseidon 527. After 16 days of a pleasant weather conditions we are now leaving Goldeneye area and sailing back to Kiel on a beautiful calm sea.

Greetings from all aboard the Poseidon!
Mario Esposito and Dominik Jasinski