Following the Trail of Fukushima Tracers: Transport Pathways, Spreading and Mixing in the North Pacific

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

The goal of this project is to use the information provided by the one-time, 2011 release of radio isotopes, and in particular, cesium (137Cs, ~30-year half-life and 134Cs, ~2-year half-life) and strontium (90Sr, 29-year half-life) from the Dai-ichi Fukushima nuclear power plants in northern Japan to better understand the pathways, mixing and transport of water in the North Pacific Ocean. The PIs will analyze surface & profile samples from the 2013 zonal CLIVAR 30°N transect for strontium; and obtain and analyze upper water column cesium (Cs) and strontium (Sr) profiles along the 2015 meridional CLIVAR line at 150°W. These observations, along with ocean cesium and iodine data collected over the last two and a half years, will be combined with satellite, drifter and float observations, an ocean model analysis and atmospheric modeling results to illuminate the details of the horizontal spread and vertical mixing that will have taken place over the 4 year period since the release of the isotopes. Intellectual Merit: The Cs and Sr observations and analysis, particularly when combined with other observed properties and numerical models, will provide a unique window from which to view water mass formation and the temporal scale of transformation within the North Pacific. This investigation seeks to better understand the fate of Fukushima radioisotopes released and deposited in the North Pacific -- how far and how deeply they range 2 to 4 years after being introduced. Although levels of this radioactivity in the ocean are not considered dangerous, the questions of where it is, and exactly how much there is, remain topics of particular interest to those who live on North Pacific shores and fish in its waters. At the same time it is asked what this unique tracer can say about ocean advection and diffusion processes. The PIs intend to use the results from the observations to improve their own model simulation and to validate disparate community modeling efforts forecasting radioisotope contamination of waters off the US west coast. Conclusions drawn concerning the variability in the mixing and spreading of Fukushima isotopes will be relevant to those seeking to understand the role of physical processes on biological production, nutrient cycling and CO2 uptake as this truly unique set of decadal-scale tracers will reveal the rates and patterns of basin-scale upper-ocean mixing and advective processes. Broader Impacts: To maximize the scientific benefit of the proposed samples through multi-tracer analysis, as well as to develop stronger ties with other labs working with Fukushima derived isotopes, and support the education of a young researcher, a graduate student from P. Masque's University of Barcelona lab will be invited to spend two semesters at WHOI to measure 90Sr activities in the North Pacific hydrographic samples. During the 1st summer of the project, a WHOI summer student fellow (3rd year undergraduate) will be invited to participate in the observational component of the project through analyses of hydrography, float profiles or altimetry. To further international collaboration with Japanese colleagues and assist in the development of new methods for reducing detection limits M. Aoyama will be invited to visit the WHOI isotope lab from Tokyo. In addition, a public website will be created on which results will be posted. All members of the group intend to engage in outreach at various levels through their continued work with the following programs: mentoring of local middle and high school students using cruise observations for science fair projects, classroom visits and public outreach presentations, interviews and talks.