Hi!

I am a 24 year old Norwegian/French PhD student, currently on the research vessel James Cook, where I will be spending the next forty days. I normally work in the Gatty Marine Lab, at the University of St Andrews.

My goal: investigating the zooplankton on the Charlie-Gibbs fracture zone (CGFZ) of the mid-Atlantic-Ridge (MAR). My contribution to the project is going to be another piece of the puzzle, explaining how surface productivity is affecting the peculiar life of the deep.

I will achieve this by sampling the pelagic (water column) realm, using a RMT (rectangular midwater trawl) which will catch the small animals which rely primarily on currents to move around. My main interest is in euphausiids (krill), a small crustacean which produces bioluminescence and aggregate in large swarms. Their claim to fame is being the principal food-source for large baleen whales. Even though these are not able to swim very quickly, they still migrate to the surface at night and to deeper waters at day. They do this to feed, and to avoid visual predators. This means that krill, and other zooplankton with similar behaviour, can contribute actively to the ecosystem of the deep sea, by feeding on the shallow primary productivity and providing food for abyssal predator and scavengers. I hope to assess the trophic level of krill species, and their main food source, by techniques such as stable isotope and lipid analysis. This will involve freezing samples at -200ºC using liquid nitrogen!

I am also interested in the impact of the unique bathymetry and surmounting fronts of the CGFZ on the species populations. Previous research indicated that deeper individuals tend to be older, so individuals on top of the ridge are usually younger. Is this reflected in the genotype of the species? Studies in other areas suggest that oceanic fronts are a source of genetic divergence. It would be interesting to detect such an effect in our study area, perhaps amplified by the barrier properties of the MAR.

All in all, it looks to be a very interesting cruise, and I can’t wait to get started with the sampling!

Tom Bech Letessier