The first set of experiments involves deploying the CTD cast, which stands for conductivity, temperature, and depth. This is the first time I've seen it, but it's a well-established oceanography instrument. A rosette with Niskin bottles (each holding 10 litres of water) is lowered into the ocean. From a computer linked to the rosette’s sensors, you “fire” pairs of bottles at various depths, filling them with water until they’re all full. Once back on the ship, they’re processed to reveal details about salinity, chlorophyll, oxygen levels, temperature, and even the microscopic creatures at each depth. The team have planned 27 CTD casts across all transects and times of the day, so although it sounds complex now, I'll get plenty of practice and might become an expert by the end of the voyage!
As a biologist, one aspect of the CTD cast is particularly exciting: the microscopic creatures hiding in them. Filtering the contents of at least one Niskin bottle from each cast through a mesh and concentrating it by thousands (from 10 liters to 4 ml) to see these creatures under the planktoscope: a microscope for plankton. This portable device, fitted with a camera, takes 20 pictures per second as water flows through, giving you a snapshot of the microscopic biodiversity in this part of the ocean. It is really fun to see all the legs and appendices these bugs have that allows them to live underwater.
Marina Klemm preparing CTD cast with 12 Niskin bottles. Photo by Emma McGuigan.