Measurements of 129I in the Pacific Ocean at Scripps Pier and Pacific Northwest sites: A search for effects from the 2011 Fukushima Daiichi Nuclear Power Plant accident and Hanford.

Radionuclides from the Fukushima Daiichi Nuclear Power Plant were released directly into the ocean as a result of the Great East Japan Earthquake on March 11, 2011. This material became entrained in surface ocean currents and subsequently transported for great distances. In June 2011, a few months after the disaster, we began a surface ocean 129I monitoring program, with samples from Scripps Pier, La Jolla, California, USA, with the expectation that surface currents originating off the east coast of Japan would eventually carry radionuclides to the La Jolla site. After 7 years of ocean transport, a distinct signal has not yet arrived at Scripps Pier. We have however, recorded an interesting systematic seasonal 129I time series record that stems from surface circulation variations along the California coast. To provide a more comprehensive picture of the 129I budget in coastal surface waters off the west coast of the U.S., we also include 129I data from the Columbia River, and offshore sites along the coast of Washington State. Anthropogenic nuclides are carried by the Columbia River into the Pacific Ocean from the vicinity of the decommissioned Hanford nuclear facility. We find highly elevated 129I/127I values in the Columbia River, downstream from the Hanford site, but this anthropogenic 129I becomes significantly diluted once it reaches the Pacific Ocean. Nonetheless, its imprint persists in surface seawater off the west coast of the U.S. that has significantly higher 129I/127I levels than other surface sites in the Pacific Ocean.

Reconstructing surface ocean circulation with 129I time series records from corals.

The long-lived radionuclide 129I (half-life: 15.7 × 106 yr) is well-known as a useful environmental tracer. At present, the global 129I in surface water is about 1-2 orders of magnitude higher than pre-1960 levels. Since the 1990s, anthropogenic 129I produced from industrial nuclear fuels reprocessing plants has been the primary source of 129I in marine surface waters of the Atlantic and around the globe. Here we present four coral 129I time series records from: 1) Con Dao and 2) Xisha Islands, the South China Sea, 3) Rabaul, Papua New Guinea and 4) Guam. The Con Dao coral 129I record features a sudden increase in 129I in 1959. The Xisha coral shows similar peak values for 129I as the Con Dao coral, punctuated by distinct low values, likely due to the upwelling in the central South China Sea. The Rabaul coral features much more gradual 129I increases in the 1970s, similar to a published record from the Solomon Islands. The Guam coral 129I record contains the largest measured values for any site, with two large peaks, in 1955 and 1959. Nuclear weapons testing was the primary 129I source in the Western Pacific in the latter part of the 20th Century, notably from testing in the Marshall Islands. The Guam 1955 peak and Con Dao 1959 increases are likely from the 1954 Castle Bravo test, and the Operation Hardtack I test is the most likely source of the 1959 peak observed at Guam. Radiogenic iodine found in coral was carried primarily through surface ocean currents. The coral 129I time series data provide a broad picture of the surface distribution and depth penetration of 129I in the Pacific Ocean over the past 60 years.

Iodine-129 in seawater offshore Fukushima: distribution, inorganic speciation, sources, and budget.

The Fukushima nuclear accident in March 2011 has released a large amount of radioactive pollutants to the environment. Of the pollutants, iodine-129 is a long-lived radionuclide and will remain in the environment for millions of years. This work first report levels and inorganic speciation of (129)I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated (129)I concentrations in surface water were observed with the highest (129)I/(127)I atomic ratio of 2.2 × 10(-9) in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of (129)I, while stable (127)I was mainly in iodate form, reflecting the fact that the major source of (129)I is the direct liquid discharges from the Fukushima NPP. The amount of (129)I directly discharged from the Fukushima Dai-ichi nuclear power plant to the sea was estimated to be 2.35 GBq, and about 1.09 GBq of (129)I released to the atmosphere from the accident was deposited in the sea offshore Fukushima. A total release of 8.06 GBq (or 1.2 kg) of (129)I from the Fukushima accident was estimated. These Fukushima-derived (129)I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future.