Bomb radiocarbon
Thermonuclear fallout and a coral in Guam
Published - Journal of Geophysical Research Oceans
Bomb-produced radiocarbon in the western tropical Pacific Ocean—Guam coral reveals operation-specific signals from the Pacific Proving Grounds
Allen H. Andrews, Ryuji Asami, Yasufumi Iryu, Donald R. Kobayashi, Neven S. Fučkar, Frank Camacho
High-resolution radiocarbon (14C) analyses on a coral core extracted from Guam, a western tropical Pacific island, revealed a series of early bomb-produced 14C spikes. The typical marine bomb 14C signal—phase lagged and attenuated relative to atmospheric records—is present in the coral and is consistent with other records (e.g. Palau, Kure, and Okinawa). However, 14C levels well above what can be attributed to air-sea diffusion alone punctuate this pattern. This anomaly was observed in other Indo-Pacific coral records, but the Guam record is unmatched in magnitude and temporal resolution. The Guam coral ∆14C record provided three strong spikes in 1954–55, 1956–57, and 1958–59 that are superimposed on a normal 14C record. Relative to mean pre-bomb levels, the first peak rises an incredible 700‰ and remained elevated for ~1.2 years. A follow up assay with finer resolution increased the peak by 300‰. Subsequent spikes were less intense with a rise of ~35‰ and ~70‰. Each can be linked to thermonuclear testing in the Pacific Proving Grounds at Bikini and Eniwetok atolls of the Marshall Islands in Operations Castle (1954), Redwing (1956), and Hardtack I (1958). These 14C signals can be explained by vaporization of coral reef material in the nuclear fireball, coupled with neutron activation of atmospheric nitrogen (14C production), and subsequent absorption of 14CO2 to form particulate carbonates of close-in fallout. The lag time in reaching Guam and other coral records abroad was tied to ocean surface currents and modeling provided validation of 14C arrival observations.
Published JGR-Oceans: http://dx.doi.org/10.1002/2016JC012043/abstract
Location of Guam with a regional map showing the study site where the coral core was extracted from the living reef structure (Double Reef). Inset of the coral core X-ray is limited to the period that was sampled for 14C (1939–2000). Double reef is an offshore outcrop that is well exposed to oceanic waters and away from major riverine inputs.
Double reef is located in the upper left of the photo, breaking the surface and away from shore.
This older, generalized map of surface currents of the Pacific Ocean provides an overview of flow patterns and how fallout from nuclear testing in Marshall Islands led to signals in Guam.
Bombs... really, really big bombs–like Bravo Shot of Operation Castle pictures at the top–created a global signal that was not kind to the world. To read up on the largest nuclear test performed by the USA, check out this Nuclear Secrecy Blog. Brilliant... Castle Bravo revisited
