The laboratory for core description of the Paleoceanography Research unit in FB1 is designed for work on sediment cores. The focus is on description and sampling. In room 8/C-007, samples are taken from sediment cores, packaged, dried and prepared for further studies. The preparation of the samples for grain size analysis, for studies on microfossils and components of the sand-sized fraction, or for geochemical analyzes is carried out in other laboratories. The Core Description Laboratory is also available for cleaning, sorting and packing of expedition equipment.
The laboratory's equipment includes a drying cabinet, a freezer, lyophilizers, a ball mill, balances, and film sealing devices.
Sediment cores are divided into 1 m long sections after retrieval and then halved lengthwise. One half is archived, the other half is described and sampled. The contact surface is smoothed with a spatula or cheese knife before the examination.
During description, the sediment composition, color, structures and fossils are identified and documented. This is done from the top to the base of the core. Layers are discriminated by changes in sediment composition and color. The position of the upper and lower limits of the layers is measured with a folding rule and referred to the top of the entire core. The folding rule is always aligned with the upper edge of the liner of the respective core section.
The colors are determined in comparison with standard color charts. The Munsell Rock Color Chart is mosty used. The colors are parameterized in the H V/C color space. They can also be recorded with an optical device and specified in the L*a*b* color space. The concentration and size of coarse components as well as their texture are determined in comparison with grain size charts. This ensures that a consistent terminology is used.
Samples are taken from the sediment cores at regular intervals. The sample spacing depends on the expected sedimentation rate and the desired temporal resolution of the data set. For studies at highest resolution, the working half of the core is cut into 5-mm or 10-mm thick slices with a knife. When collecting samples for routine investigations, cut-off 10-ml injection syringes are used. We hold the piston with one hand and press the cylinder into the sediment with the other hand until the required volume is reached. The syringe is then rotated by 180 degrees to shear the sample in the syringe off the surrounding sediment. We then insert a micro-powder spatula into the sediment on the outside of the cylinder and rotate it by 90 degrees. Air can enter along the hole created by the spatula, and the syringe with the sample can be easily pulled out. The sample is squeezed out of the syringe and transferred to a plastic beaker. The hole in the sediment core is then filled with closed-cell foam.
The beaker and sample is weighed and their volume is noted. The sample is then frozen in the beaker for freeze-drying at -20 degrees or dried in a drying cabinet at 60 degrees. The dried sample is weighed again. Sediment physical properties are calculated from the dry weight, the water loss during drying, and the sample volume.
The beakers with the frozen samples are covered with a lint-free wipe and exposed to a high vacuum in the lyophilizer. The resublimated water is bound in a cold trap at -60 degrees. Freeze drying takes more than 24 hours. The samples retain their shape and color. After freeze drying, the samples are riddled with numerous microscopic cracks that run around larger components. The salt from the pore water remains in these cavities as tiny crystals or crusts. If freeze-dried samples are covered with distilled water, the sediment breaks down into small scales in just a few moments and can be washed easily and quickly without wasting a lot of water.
After processing, the archive and working halves of the cores are wrapped in cling film or stretch film and then sealed in a polyethylene film tube. Packed like this, they are well protected against desiccation. The core halves are stored in core storage tubes, i.e. D-tubes, at 4°C.
