Abstract
The Iceland Basin region of the N. Atlantic is important for two reasons. Firstly, the biological carbon pump here exhibits one of the strongest signals of any of the worlds oceans. Secondly, the food-web of this region supports the important herbivorous calanoid copepod, Calanus finmarchicus, that forms an important dietary component of the commercially important juvenile Cod stock. Both carbon export via the biological carbon pump and the transfer of energy to herbivorous zooplankton depends primarily on the amount of nitrate-based new production relative to total primary production. However, climate change scenarios for this region predict that ocean stratification may become stronger, and as a consequence, the upward flux of nitrate may become constrained. Furthermore, there are some recent indications that new nitrate-based production in this region may be somewhat iron limited. To test these ideas, we therefore undertook a cruise to the Iceland Basin region in July / August 2007, to examine controls on new production. We undertook measurements of phytoplankton new and regenerated production using 15N-NO3, 15N-NH4 and 13C tracers and we compared nitrate uptake with the upward diffusive flux of nitrate determined from turbulence measurements. We also assessed phytoplankton new production rates in response to ambient light and Fe gradients and further assessed Redfield C:N fixation rates from duallabelling (13C, 15N) experiments since the Redfield stoichiometry of particle flux has important consequences for relative rates of carbon and nitrogen export. In this paper, we report on some of our key findings.