Award: OCE-1233903

The chemical makeup of the world's oceans is important as the oceans are home to a wide range of plants, animals, and microbial life. The chemical makeup of the oceans and different portions of the oceans are important characteristics of the environment in which these life forms live. We would thus like to understand the cycles of the naturally-occuring elements within the ocean, how they enter the ocean, how they are removed from the ocean, and how they are re-distributed within the ocean. In this study, we have measured concentrations of forms of particular elements (thorium and protactinium), which have extremely low concentrations in ocean water. The concentrations are so low (in some cases about a part in a billion of a part in a billion) that, as part of the project, we needed to refine methods in order to make the measurements. We did so successfully. We wished to measure some of these particular forms of elements because they have the unusual property that they are produced within the ocean at a constant rate, everywhere within the ocean. By measuring the concentrations of these unusual forms of elements, we can therefore learn about how they are removed from the ocean and how they are re-distributed within the ocean. In this study, we collected sea water from many depths across the Pacific Ocean. In addition, we carefully filtered the particles within the sea water. We analyzed hundreds of sea water samples and samples of the particles. Our measurements show that one of the main ways that these elements are removed from the ocean is related to hot springs that vent into the ocean at the crests of mid-ocean ridges. The hot water from these vents can alter the chemistry of the ocean over stretches of thousands of kilometers. Small solid particles can form from mixtures of vent water and sea water and settle to the sea floor. Our study shows that the elements in question are removed along with these particles, over a large swath of the Pacific Ocean. Our study also shows that the elements in question are added and removed from the eastern portion of the Pacific by wind-blown dust. These findings would be considered the intellectual merits of our study. The broader impacts of our study include development of refined measurement methods to assay very low levels of certain elements, without significant contamination and training of scientists in these refined methods. Last Modified: 03/31/2016 Submitted by: R. Lawrence Edwards