Microbial and biochemical controls on the sinking rates and export of marine aggregates

Sedimentation of aggregates from the upper ocean is a key process in global biogeochemical cycles and considerable research has been conducted on material collected from marine sediments and both moored and free drifting sediment traps. However, processes that occur within the water column prior to deposition to sediments, and in particular factors controlling sinking rates of marine aggregates, are less well understood. Different biochemical components have different densities and hence different specific gravities in sea water. Lipid is less dense that sea water and hence provide uplift. By contrast, carbohydrates and proteins typically have specific gravities equal to or greater than that of sea water, and hence the balance between the relative amounts of the major biochemical components will influence the density and sinking rates of particles. The nature, chemical composition and density of sedimenting particles, and interactions with mineral material, are also key influences on their bio-reactivity and fate within the water column. Microbial activity is key in this respect with microbial activity promoting particle aggregation and export. Digestive transformation in the guts of zooplankton, also dramatically alters biochemical composition, with preferential removal of intracellular versus cell-wall components, and creation of faecal pellets that are quite different in reactivity, composition and sinking rate from intact algal cells.

The PhD will particularly suit enthusiastic candidates with environmental, chemical or biological background. Skills employed during the studentship will be broad based, combining field and laboratory experimentation with a range of analytical techniques (i.e. microbial culture, molecular phylogeny, GC-MS, HPLC and HP-DSC) for which full training will be given. The successful candidate will be expected to spend time in both Oban and Edinburgh during the course of the studentship and engage with an active team of researchers.