Award: OCE-1131731

The chemistry of the oceans is highly variable in space and time. This is particularly true for biologically active elements in the oceans, including nutrients like phosphorus and nitrogen. But it is particularly true for the biologically essential metal iron. Iron is quite insoluble in seawater and its concentrations are low. Nevertheless, it is so abundant in the earthÆs crust, that there is a constant supply from the continents. Until recently, scientists focused on inputs near the surface – from dust and rivers. But results from this project reveal that inputs in the deep ocean – rather than shallow- are very important. The project revealed two vast plumes supplying iron and other elements to the oceanÆs interior from deep sources. One arises from the continental slope off western South America. The other arises from the east Pacific Rise, a mid-ocean spreading center containing a large hydrothermal field. These plumes extend thousands of kilometers through the deep ocean. Recent work by scientists who model ocean circulation suggests that much of this iron ultimately finds its way to the sea surface where it helps stimulate biological growth. The results help us to understand the interaction between surface ocean processes and deep ocean processes in controlling the supply of nutrients and essential minerals like iron to marine food chains. Marine geochemists now realize that it is very difficult to understand phenomena like these plumes in isolation. Comparing the concentration and transport of elements like iron with other elements within the plumes provide insight into their sources and eventual fate. For this reason, the international GEOTRACES program was conceived and is now a cornerstone of oceanographic research in over a dozen nations. This cruise was an important US contribution to the program. Thirty research groups in the Unites Staes were supported to make a comprehensive series of measurements. Many substances currently being analyzed will provide new insights in the coming years. Last Modified: 09/03/2015 Submitted by: James W Moffett