Trace Metal

Trace metals are metallic elements present in seawater at very low concentrations, from picomolar to nanomolar. Some are bioessential micronutrients, iron, zinc, copper, cobalt, manganese, and nickel, that limit phytoplankton growth across vast ocean regions; iron limitation governs primary production in the Southern Ocean and equatorial Pacific. Others, cadmium, lead, and mercury, are toxic with no biological role. The same element can switch between roles by concentration and speciation: copper is a micronutrient at trace levels but toxic to algae as free Cu2+. Clean sampling under the GEOTRACES program maps their distributions.