Day 21 bobbing about on the Southern Ocean and, as gale-force winds whistle around the ship, bringing sampling to a halt, I thought I’d use this opportunity to talk you through a typical day of science at sea.
My shift (day shift) is now working well as a team, and our sampling routine is becoming more and more fluid with every gear deployment. Our 12-hour shift begins at 7am, and we immediately take over tasks from the night shift. Because sampling is a continuous 24-hour operation, you never know what you will start the day doing, but sampling occurs in a circular manner, following a set sequence.
First comes a quick survey of the seabed using the ship’s sophisticated multi-beam sonar system. The beautiful high-resolution map that results is valuable in its own right, but also helps us to pin-point exactly where we’d like to collect samples from.
Once a site is chosen, the CTD (Conductivity, Temperature, Depth) is first to enter the water. This is a cylindrical tubular metal frame covered with numerous expensive-looking scientific instruments that measure almost everything you’d ever want to know about sea water – depth, temperature, salinity, oxygen concentration, and chlorophyll concentration, amongst others. This helps to put our sampling in a broader environmental context.
Next follows the underwater camera system, which has the perhaps unfortunate acronym of SUCS (Shallow Underwater Camera System). SUCS is depth-rated to 1000 m and consists of a metal tripod frame with a downward-facing HD video mounted at the centre, flanked by two lights. The camera is towed slowly along a transect, descending to the seabed every 10 m for a photograph to be taken. Not only can these images be analysed scientifically, but they also offer a tantalising taster of what we can expect to bring up in the following trawls.
We use an Agassiz Trawl (AGT) to sample the larger animals (more than about 2 cm) living on the seabed. The AGT is a simple piece of technology. It consists of a relatively small (1.5 m width) metal frame with sledge runners connected to a sack-like net that collects any large animals that pass through the mouth of the frame. The AGT is towed slowly (~0.5 mph) on the seabed for 10 minutes. Once retrieved on deck, any animals collected in the net are quickly sorted into groups, given a unique identifier, counted, weighed and appropriately preserved for future use.
Every third AGT, the Rauschert dredge is deployed alongside. This dredge is the little brother of the AGT, being about 10 times smaller in volume. It is used to sample the tiny animals living on and in the seabed, and so is equipped with a much finer mesh size. There are usually too many small animals to process on the ship, so samples taken with this little dredge are preserved in alcohol to be looked at again at a later date.
Finally, at the end of the sampling sequence, the epi-benthic sledge (EBS) is lowered to the seafloor. This is the heaviest piece of equipment we use (about 550 kg), and consists of a long tubular metal frame with sledge runners and two fine mesh nets placed one on top of the other. The lower net collects animals from close to the seafloor, whilst the upper net takes animals from slightly higher in the water column. Like the little Rauschert dredge, the EBS is designed to sample the smaller animals that call the deep sea home, and, these being very numerous, the sample is usually quickly preserved in alcohol for future sorting.
It is impossible to escape the fact that there is an irony in this sampling that we carry out. Other than the CTD, all the equipment that we lower onto the seafloor causes some amount of disturbance to the life there. This ranges in magnitude from small for the camera system, to relatively large for the Agassiz trawl. Yet, at present, this is the best method we have of learning about what is living on the seabed below – from the very small to the very large. Ultimately, the data collected by our sampling will be used as evidence to determine whether or not the areas we have examined require special protection from human activities. For a small amount of damage caused by our sampling, we may be able to guarantee the long-term protection of an area. In fact, preliminary analyses of the camera images show that the majority of sites sampled so far are inhabited by relatively large abundances of animals deemed vulnerable to anthropogenic disturbance, and so may meet the criteria laid down by the ‘Commission for the Conservation of Antarctic Marine Living Resources’ to be worthy of protection. Real-world relevance and impact like this makes my work all the more fulfilling.