Award: OCE-1756415

Everyone knows seawater is composed of several salts, but it also contains ALL of the biologically essential elements as well, such as zinc and copper. This seems obvious, since if it didn’t, there would be no marine life. But chemists and biologists have marveled at how scarce some of these elements are and how organisms manage to acquire them. Our research shows that this is a particular problem for copper. Copper is more abundant than many other "trace" elements in surface waters, such as iron and cobalt. But we found that copper is mostly tied up in chemically inert forms. We tried adding massive quantities of copper binding substances to seawater and waiting for weeks to extract the copper from sweater – and often recovering only a tiny fraction. In the central Pacific – our work within the GEOTRACES program showed that up to 90% of the copper is inert. What is holding on to the copper so tightly under natural conditions? We are not sure, but it seems like copper is slowly and irreversibly incorporated into inert forms while more reactive forms are removed onto sinking particles (primarily biological) that sink and are removed. Why doesn’t this inert copper just accumulate indefinitely like the major salts do? It turns out that exposure to sunlight destroys the inert fraction and renders the copper the copper reactive and biologically available. That is fortuitous, since it releases the Cu when organisms need it the most, in sunlit surface waters where it enters the food chain. Our findings require a complete rethinking about how copper interacts with organisms and other chemicals in the sea. We think inert copper may be important in other settings as well. For example, engineers have developed bioreactors that can convert nitrate – a contaminant in wastewater – into benign nitrogen gas. But if the bacteria catalyzing that transformation cannot acquire copper to make a key enzyme, then all of the nitrate ends up as nitrous oxide, a potent greenhouse gas. So we need to learn a lot more about what this material is, why light breaks it down, and what other factors control its distribution. Rintaro Moriyasu pioneered this work, including developing the method, for his Ph.D. He now works within the federal government on environmental assessment. Last Modified: 10/31/2022 Submitted by: James W Moffett