Proposal Abstract:
Nutrient and iron addition experiments are a basic oceanographic tool that has resulted in major advances in our knowledge of controls on oceanic productivity and carbon cycling. However, most of the shipboard and in-situ work carried out to date has involved additions of limiting nutrients that are one to two orders higher than ambient levels, resulting in massive blooms that are not typically observed in the natural ecosystems being investigated. For this reason, it is necessary to understand the consequences of continuous iron and nutrient inputs at realistic concentrations on phytoplankton community structure and oceanic carbon cycling. The principal investigators from the University of Delaware and the University of Charleston will carry out this type of experiment in the Southern Ocean utilizing their natural community chemostat system. This system delivers iron and nutrients at natural levels to incubated shipboard experiments at continuous flow rates that simulate real-world vertical advection processes. The specific goals of the proposed research is to address the following four questions: (1) How does phytoplankton species composition respond to changes in iron concentrations in upwelled water?; (2) What effect will variability in upwelling rates at a give iron concentration have on community structure?; (3) How does iron chemical speciation affect the composition of phytoplankton communities?; and (4) How will a changing iron supply affect the production of biogenic sulfur?