Award: OCE-1649439

In this project we successfully measured the stable isotopes of three metals in the South Pacific Ocean: iron, zinc, and cadmium. Each of these metals is a crucial micronutrient for algae which live in the ocean and are the base of the marine food chain. By studying their stable isotope ratios (denoted as δ56Fe, δ66Zn and δ114Cd), we can understand how these biologically important elements enter the ocean and how they leave the ocean. For example, our measurements of iron isotopes demonstrated that a large amount of iron enters seawater from sediments on the seafloor near Peru, and that this iron travels thousands of kilometers into the open ocean. Iron is an important nutrient for algae in the surface oceans, so it was interesting to see how much iron comes from mud on the seafloor, and to know that iron supports the growth of algae, which in turn supports the growth of fish in important fisheries. Our measurements also showed a large supply of iron and zinc from hydrothermal vents (underwater volcanoes) at a location known as the East Pacific Rise. By tracking the direction in which this iron and zinc flowed in the deep ocean using isotopes, we were able to guess how much might eventually reach the surface. The biological uptake of zinc and cadmium are not very well known, so our measurements of these metals and their isotopes are now being used in computer models to better understand exactly how algae remove these elements from seawater, and how they are released back into seawater as dead algae sink out of the sunlit surface ocean and decay in the deeper darker ocean. This work supported the studies of several undergraduate students, graduate students, and postdocs, who all helped to measure metal isotopes in seawater and interpret their results. Last Modified: 11/29/2018 Submitted by: Seth G John