Matrix experiments were conducted to determine the role of trace metals in limiting phytoplankton growth rate in seawater collected from the deep nitrate maximum (800 m, 25 µM nitrate) off the North Carolina coast. Additions of FeCI3, MnCI2, and chelators (EDTA and NTA) stimulated the growth of unialgal cultures of Chaetoceros socialis or of a natural phytoplankton community inoculated into this seawater....