The March 11, 2011 earthquake and resulting tsunami made substantial damage to the Fukushima Daiichi nuclear power plant, and as a consequence there were significant releases of iodine, cesium, cobalt and other radioisotopes to the environment. Radionuclides were released to the atmosphere as well as the ocean. For atmospheric releases it was only a matter of days before they dispersed in the northern hemisphere. Isotopes detected on EPA air filters at many US sites included 137Cs, 134Cs, 132Te, 132I and 131I. While the currently observed radiation levels do not pose a health risk for the US population the released activities are easily identified over the long-term background levels in the atmosphere. Releases so far have been episodic and highly variable, making predictions of spreading and deposition patterns difficult.

With funding from this Grant for Rapid Response Research (RAPID), researchers at the University of Hawaii at Manoa will monitor seawater near Hawaii in the central Pacific Ocean in order to establish a dataset of selected key isotopes. Its proximity to Japan makes Hawaii an obvious, important monitoring point. They will collect coastal and offshore water samples as well as particulates from ocean traps. Additionally, they will analyze samples provided to us by investigators from Midway and Guam. This dataset would become a part of a global effort initiated by colleagues at the Woods Hole Oceanographic Institution to establish an east to west network of sampling stations in the Pacific an Atlantic Oceans. Since releases from Japan have been registered in Hawaii as early as March 22, it is essential that sampling and analysis begin immediately in a coordinated and quality controlled manner.

Broader Impacts: The findings of this study will be incorporated into the database of results collected in the Pacific as well as the Atlantic Oceans to build the understanding of the inventories and behavior of fission-produced radionuclides in the marine environment on a global scale. The study will include international collaboration with investigators from Japan, the IAEA, Czech Republic and scientists from WHOI, USGS, Guam and others.

Project Report

. Significant amounts of radionuclides escaped to the atmosphere and, by direct discharge or leakage, to the ocean. From these, Cs-134 (half-life 2.07 a) and Cs-137 (half-life 30.08 a) are important Fukushima-derived radiation tracers in the ocean because of their radioactive-conservative behavior and large quantities released. Our objectives were to assess surface seawater Cs-134 and Cs-137 patterns in the central and western North Pacific Ocean to: 1) determine atmospheric fallout patterns and levels 2) monitor dispersion patterns of radioisotopes released to the ocean across the Pacific Ocean 3) use cesium as isotopic tracer of ocean currents We have developed new high-sensitivity methods for cesium determination in the marine environment that have since been adapted by several laboratories. We collected seawater samples for radiocesium analysis in Hawaii as well as in the central and west Pacific. Based on samples collected in March and April 2011, we found that atmospheric fallout did not leave a significant radiocesium footprint in the surface ocean at the investigated regions (Guam, Hawaii, Midway Islands). We were able to define the southern boundary of the atmospheric fallout signature in the central Pacific at a latitude of about 35 degrees north. Results from the west Pacific indicated that radionuclides undergo significant dilution and dispersion within short distances from their release point. At a distance of 1,000 km from Japan the observed Cs-134 in years 2011 and 2012 were between 1-10 Bq/m3 in comparison to several thousands of Bq/m3 at 100-300 km and millions of Bq/m3 at the discharge site. We found that the eastern edge of the plume was at a longitude 162 degrees west in 2012 resulting in a longitudinal spreading rate of 2,500 km/yr. Our results also showed that the southern boundary of the Kuroshio and Kuroshio extension currents effectively prevented the southward spreading of radionuclides released to the ocean. The Kuroshio extension and North Pacific currents have been deflected north of the main Hawaiian Islands so the radiation dispersed north of them. This has implications on cesium activities measured near the main Hawaiian Islands, specifically that no Fukushima-derived radiation was detected in their vicinity between March 2011 and October 2013. This was confirmed by our time series monitoring of ocean cesium activities in Honolulu and offshore, about 100 miles north of Oahu. We analyzed surface ocean samples from Station Aloha and Honolulu originating from fallout from nuclear weapons tests in the last century. Cesium-134 was never detected in any of these samples and we could conclude that contrary to model predictions, the radiation plume has not reached Hawaii within 30 months of its release from Fukushima. Our results also make us conclude that radiocesium concentrations in the Pacific Ocean are significantly diluted due to dispersion and pose no health risks to the US population. In our effort to better inform the public about our results these are presented at the following website: http://oos.soest.hawaii.edu/pacioos/projects/fukushima/index.php

Agency
National Science Foundation (NSF)
Institute
Division of Ocean Sciences (OCE)
Type
Standard Grant (Standard)
Application #
1137412
Program Officer
Donald L. Rice
Project Start
Project End
Budget Start
2011-05-01
Budget End
2013-10-31
Support Year
Fiscal Year
2011
Total Cost
$94,637
Indirect Cost
Name
University of Hawaii
Department
Type
DUNS #
City
Honolulu
State
HI
Country
United States
Zip Code
96822