Methods
We will conduct two cruises to the Ross Sea, one is summer and one in austral spring, and conduct both experimental and observational studies. We will sample regions where iron and carbon dioxide is high, as well as regions where both are low, and determine the irradiance regime in each. If possible, we will also sample regions with high iron and reduced CO2 levels, as well as low Fe and high CO2 concentrations (both are relatively unusual states). The observations should allow us to determine the most important factor in controlling phytoplankton composition, a major factor in controlling biogeochemical cycles in the ocean.
We also will sample water and manipulate CO2, Fe and irradiance levels within deck-board semi-continuous mesocosms. This will directly test the interactions among the three variables.

Measured Parameters

Many different measurements were made by the group and include the following:

• Temperature, salinity, density
• Nutrients (nitrate, nitrite, silicate, phosphate, ammonium)
• Iron (dissolved, complexed, particulate), Cobalt, Cadmium
• Chlorophyll (total and < 20 µm)
• Particulate organic carbon, nitrogen and phosphorus
• Biogenic silica
• DMS, DMSP (all pools)
• CO2, pH
• Photosynthetic performance via fluorescence
• Primary production via 14C
• Phytoplankton pigments via HPLC
• Phytoplankton composition via microscopy
• Bacterial and viral abundance
• Photosynthetic responses