A number of trace metals in seawater are essential micronutrients for phytoplankton and heterotrophic bacteria (e.g., Fe, Zn, Co, Cu, Cd, Mn). If the availability of one or more of these metals is too high they exert toxic effects while too little can limit productivity. Because phytoplankton species differ in their metal requirements and tolerances, changes in metal concentration or chemical speciation should have a strong influence on the composition of plankton assemblages as well as the net carbon transport from surface to deep waters. My research group studies the chemistry of bioactive metals in seawater and lake waters, their effects on phytoplankton and bacteria and, in turn, how these factors may alter ocean optics and the remote sensing of phytoplankton distributions by satellites.