9.8.2019 – Great dirt work: Processing sediment samples

Last time we described how we got the first valuable sediment samples on board with the Multi-Corer (previous post). Here is a look at how they are processed so that they are not just dirt from the bottom of the sea, but a valuable glimpse into the past of the respective sea area. Some of the samples are directly placed in one of the refrigerated containers for later laboratory analysis at home. Other samples are processed right away. The first step is to sample the pore water from between the sediment particles through little holes in the sample tube for further analysis. In addition, we cut some samples into handy portions one or two centimeters thick and fill them into sample bags.

The multi-corer only samples the top fifty centimetres of the seafloor. If we want to “dig deeper” – and thus look further back in time – we need the so-called gravity corer. This is a long steel pipe with many weights at the upper end and a plastic pipe inside, the “liner”. The whole thing is lowered with a winch rope and when it hits the seabed, the weights push the steel pipe into the sediment. Sounds simple, but it isn't – because weight and winch speed must be set exactly right by the operator for the respective sediment type. If not, the gravity corer will either sink too deep into the sediment so that we do not know at what depth the sample begins – or, if the sediment is too hard, the steel tube will not penetrate deep enough. With hard sediments, you can even bend the steel tube if the winch speed is too high. If everything went well, however, and the gravity corer is safely back on board, the liner is pulled out of the steel pipe and cut into several sections along with the sediment core inside. Smaller samples are taken directly after cutting the sections.

Once the core is completely divided up (and the deck has been cleaned of all sediment), further processing can begin. To take a closer look at the sediment layers, the sections are split in halves. This is done by using a special rig with two saws to cut the liner. The sediment core is then cut with a steel wire and the halves are carefully flipped open and separated from each other. The halves can either be stored for later analysis or, as with multi-corer samples, can be sliced and packed in bags.

 

(Photos: IOW / R. Prien, please click for a larger view)