Award: OCE-1139902

This project was funded in response to the Tohoku Earthquake in March 2011, and the resulting accident at the Fukushima Nuclear Power Plant (FNPP) which lead to both immediate release of radionuclides to the atmosphere and, longer term, release from contaminated groundwaters surrounding the stricken facility into the oceans. For the radionculides released to the atmosphere, dispersion was widespread. Sensitive detectors on the East Coast of the United States were able to pick up traces of incident radiation within a week of the accident and within a month similar detections were made in South Korea, as the radionuclides completed a first circumnavigation of the northern hemisphere. What was of more concern to this study was what happened to the higher concentrations of radionuclides released to the oceans close to their source in the weeks and months following the initial accident. As part of a larger study that also surveyed inventories of radionuclides in the surface waters of the oceans and in fish in local seas, this project sought to collect samples to study what concentrations and rates of sedimentation of radionuclides there might be in particulate matter – whether attached to continental dust or biologically derived material from the sunlit upper ocean – that was being transported into the oceans where it might otherwise be overlooked: either stored in seafloor sediments or recycled in the ocean interior. To achieve this my team collaborated with Dr Makio Honda, a colleague at the Japanese Agency for Marine Science and Technology (JAMSTEC) in Tokyo, Japan. In the immediate aftermath of the earthquake, JAMSTEC had research ships available to put to sea but rather compromised access to infrastructure on shore. Under our NSF RAPID grant we were able to assemble a complete array of the sampling equipment required in component form, airfreight the entire package to Japan in under 6 weeks, and fly to Yokohama to meet Dr HondaÆs ship in port where we helped assemble the gear ready for deployment. The equipment package consisted of two sediment traps - time series sampling devices that operate like large funnels with wide upper surface areas to capture sinking solid material and a narrow stem at their base. Anything solid falling into the top of the funnel passes through the stem and gets collected into a sample bottle at the base of the trap. Then, every two weeks, a carousel rotates to line up a fresh sample bottle while all the other sample bottles are covered so nothing gets in or out. In this way, when we analyse the samples, we know how much material arrived, when, within each sampling period. For the Fukushima study we used two sediment traps, one to collect material sinking as far as 500m down in the water column and the other to collect material sinking to 1000m depth. The entire instrument package was held in place on the seafloor by attaching the devices to a steel cable with an anchor weight at its base and a series of glass spheres (high pressure versions of fishermanÆs floats) at the top of the array to keep the whole instrument package upright and vertical. The equipment was deployed from Dr HondaÆs research cruise off the coast from the FNPP in July 2011 and samples were collected from July 2011 until July 2012. The full extent of my own laboratoryÆs contribution, beyond procuring the equipment and ensuring the samples were collected was to analyse the composition of the material obtained and to calculate what proportion of the total mass of each sample was made up of (a) soft organic matter, (b) hard shelly material - either made of calcium carbonate or opal (silica) or (c) detrital material whether present as dust blown in by the wind to the ocean surface or sediment washed offshore by rain, rivers or currents. Of most interest, however, were the results from my colleague Dr Ken Buesseler at WHOI who took my samples and analysed them by gamma counting for the two most abundant isot...