Award: OCE-1735445

Project Outcomes Report Award Number:1735445 Project Title: Quantifying Upper Ocean Export and Remineralization of Bioactive and Particle Reactive Trace Elements along the US GEOTRACES Tahiti to Alaska Transect PI: Ken Buesseler, Woods Hole Oceanographic Institution The ocean plays a major role in the cycling of carbon and other elements on Earth, including the transfer of materials from the surface ocean to the deep sea associated with sinking particles, or so-called marine snow. This proposal made key measurements of the amount and spatial distribution of these transport processes as part of a larger international oceanographic research program called GEOTRACES. In this case, samples were collected on a roughly 2-month research expedition between Alaska and Tahiti in 2018. We measured the differences between sites and at different depths using an approach pioneered by this lab, that takes advantage of a naturally occurring form of the element thorium, called thorium-234. Simply put, the lower the levels of thorium-234 we measure, the faster it is being carried to depth in association with the sinking marine snow particles. Since thorium-234 has a known source and loss from naturally occurring radioactive decay from uranium-238, we can use it as a clock to measure these loss rates. By measuring the amount of thorium-234 and other elements on marine snow particles (here we compare thorium-234 to carbon, nitrogen and several trace metals), we can quantify the removal of these other elements. The intellectual merit of the project includes the ability to make comparisons between these data and prior studies in order to have a better view of the cycling of particle associated elements in the ocean. Other GEOTRACES will be able to compare their results with this study to elucidate further specific controls on trace elemental cycling that is at the core of the GEOTRACES program. This project was the main focus of a PhD thesis of Jennifer Kenyon, a WHOI/MIT graduate student. She and another undergraduate student were mentored as part of the broader impacts of this project. She also produced a graphic novel as part of a science-art collaboration at MIT that is now available that can be used to engage public audiences in the motivation and science behind the project. Results showing wide differences along the sampling transect in the amount of particles sinking out of the upper ocean have been presented at several virtual meetings and conferences, and are being brought to academic publication form as part of this PhD thesis. Last Modified: 12/16/2021 Submitted by: Ken O Buesseler