Objective 3:
The upwelled and surrounding waters will be sampled for viral, algal, bacterial and microzooplankton biomass, taxonomic composition and activity (production and respiration) linked to concurrent measurements of in vitro and in situ changes in trace and biogenic gas concentrations, in order to identify the important trace gas production and loss processes mediated by the plankton community. We will estimate bacterioplankton production as well as the relative contribution of dominant bacterial groups using amino acid radiotracers and flow cytometric sorting.

These bacterial groups will then be phylogenetically characterised and quantified by fluorescent in situ hybridisation (FISH) with rRNA oligonucleotide probes, or if necessary the complete rRNA cycle. We aim to quantify the number of bacteriochlorophyll containing cells and estimate their contribution to total bacterioplankton production. We will bioassay concentrations and turnover rates of organic (amino acids, sugars etc.) and inorganic nutrients (phosphate, iron etc.) to assess the role of nutrient limitation. We will also estimate protist grazing using prey pulse-chase isotopic labelling and size fractionation techniques. In order to determine the impact of upwelled water on DMSP production, and the fate of the DMSP production through viral lysis and grazing, we will determine the temporal change in DMSPp, DMSPd and DMS within the upwelled water compared to adjacent waters, the taxa responsible for DMSP production, viral abundance and genetic diversity, µzooplankton grazing impact on DMSP-specific phytoplankton, viral impact on DMSP-specific phytoplankton, and grazer and viral production of dissolved DMSP and DMS. We aim to develop a comprehensive model of the role that upwelling water plays in DMS sea to air flux, linking to the proposed work by SOLAS collaborators on photochemical transformations (Uher), sea to air flux estimates (Fowler) and modelling (Allen). Nitrification is a major source of N₂O to the atmosphere, and so we will examine the influence of enhanced nutrient availability on the rates of ammonium regeneration and nitrification. Previous unpublished data demonstrated elevated rates of ammonium regeneration associated with upwelling and in situ nutrient addition experiments. Preliminary results suggest a similar enhancement of nitrification under these conditions. Pending additional funding  (Nightingale) we will also investigate the flux of OVOCs in relation to bacterial activity.