Gravity core sub-sampling

As mentioned earlier by Marion, the core sub-sampling was divided into two different procedures : pore water sampling and solid phase (sediment) sampling. It took us the whole day on friday to sample the entire 6m core, and despite a few minor difficulties, the operation was a success!

Pore water sampling

Pore water was collected with rhizons that act a bit like the root of a plant by sucking up water, while the other end is connected to a tube that has been vacuumed. Pore water was sampled every 25cm for the 5 first segments of the core, and then every 10 cm for the upper-most segment, for a total of 30 samples.

Two rhizons connected to exetainers for pore water sampling

We started with the bottom segment of the core and the sediment was so compact that the rhizons would not penetrate! We then had to drill holes through the core to be able to insert the rhizons and everything went well eventually. The pore water was distributed to smaller tubes of different colors, each type corresponding to a specific analysis. The tubes were finally stored at appropriate temperature depending on the analysis to be performed (4°C or -20°C).

Sediment sampling (solid phase)

Small windows of approximately 3-4 cm of width and half-diameter long were cut into the core’s tube to prevail the sediment from being disturbed too much and to minimise the exposure to the surrounding environment. With the use of cut-syringes we sampled specific volumes of sediment – 2mL or 5mL depending on the analysis.

Sampling syringes for the solid phase

Sediment being sampled for solid phase analysis

To stop the methane production by bateria we transfered the sediment into vials containing a saturated solution of NaCl. The sediment sampled for cell analysis was transfered into falcon tubes containing PFA (paraformaldehyde) and a 35 g/L NaCl solution.