The distributions of dissolved trace metals
Many dissolved trace metals such as iron, nickel, cobalt and manganese are essential nutrients for phytoplankton and bacteria. Some metals may also be toxic, depending on the particular chemical species of that metal. This is the case for copper. We are interested in exploring the distributions of dissolved trace metals in seawater, in environments ranging from the open ocean (where these metals are particularly scarce) to nearshore or coastal environments (where many metals are present in relatively high concentrations). Trace metals often play different roles depending on the environment where they are sampled. Iron, for example can limit phytoplankton growth in many regions of the ocean such as the Southern Ocean near Antarctica, or other upwelling regions. However, copper can often be toxic to phytoplankton growth in many harbors and marinas due to its high concentrations from anti-fouling paint on boat hulls. In addition to measurements of total dissolved trace metals, we also measure the organic speciation of these metals, in order to determine their chemical speciation. The different organic species present in seawater can affect how the metal cycles. Some organic forms of copper for example are not toxic, yet the uncomplexed version is detrimental to phytoplankton growth. The organic forms of cobalt in seawater may also be important nutrients such as vitamin B12. Thus, determining the speciation of dissolved trace metals is essential for understanding their role in the marine environment. Techniques we use for these projects are voltammetry (cathodic stripping voltammetry), and inductively coupled plasma mass spectrometry (ICP-MS).