Mireille Consalvey PhD Thesis - University of St Andrews

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Stiff foil was also used to remove a small area of sediment/biofilm, which
was flash frozen in LN2 and later viewed under the LTSEM (Paterson 1995).
2.2.2. Cryolanding
Traditionally, sediment samples were collected by syringe coring (Joint et
al. 1982), however, this causes distortion to the sediment surface. Therefore, a
technique was pioneered by Wiltshire et al. (1997) to freeze samples without
disturbing the sediment structure. Furthennore, this technique was designed to be
used in situ to ensure that samples are representative of natural conditions and
not a result of transportation/laboratory artefacts.
The Cryolander consists of a brass tube (Figure 2.3) and a gauze plate
supporting cotton wool. A small amount of liquid nitrogen is poured over the
cotton wool, causing the liquid to vaporise. The vapour sinks and freezes the
sediment surface. Once the surface is frozen (and therefore fixed) more liquid
nitrogen is poured onto the sample to freeze a disk of sediment. This is removed
from the Cryolander and stored in liquid nitrogen prior to further analysis. The
cryolanding process can take up to 10 min.
Samples were fractured (using a hammer on the underside of the disk)
under LN2 and examined under the LTSEM, or sawn into blocks (using a
lapidary saw) of approximately I cm 2 to be sectioned using a freezing
microtome. At all times exposure to room temperature was kept to a minimum.
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