We are indebted to Tamara Adame, Mara-Teodora Feodor, Cyrielle Houard, Brian Kirk, Camille Laquerriere, and Leigh Tobin for their heroic effort in collecting the sediment samples in the Bravo crater. We thank Indies Trader for providing the infrastructure, transportation, and overall support for the dive project. We thank the people of Bikini for supporting this project, and the Marshall Islands Nuclear Commission for guiding us through the approval process.
Samples collected near the crater edges were more grainy therefore, these samples are more likely to have sediment mixing from differing sediment depths (ranging, at most, over the full 0 to 25 cm). However, the sediment composition over the majority of the Bravo crater did differ significantly from the composition near the edges.
Therefore, it is likely more accurate to assume that the samples in this study are represented by considering that the composition originated from sediment located between 15 and 25 cm from the sediment surface rather than closer to the surface.
Although sediment mixing throughout the 25-cm depth is certainly possible, it did appear that for the vast majority of the core samples the solid hard mud, with pulverized consistency of the lagoon sediment, is more likely not to have mixed. All subsamples were mailed as a batch to Gel Laboratories for isotopic analysis. Subsamples were transferred to a 100-mL plastic centrifuge tube. Subsamples of sediment were removed from the deep end of the core, corresponding to 15 and 25 cm from the lagoon sediment surface. Once collected, cores were transported intact back to Columbia University. The total yield from nuclear-weapons tests performed in the few-kilometer-diameter Bravo crater region corresponds to one-third of the total yield from the entire US nuclear weapons testing program in the Marshall Islands. The range of yields was from 1 to 15 megatons for the 7 nuclear weapons detonations in the Bravo crater vicinity ( Table 1 and Fig. As a result, today’s radioactive contamination from the Bravo crater comes from a complicated mix of nuclear weapons tests detonated in the area. These tests likely knocked the southwestern rim of the initial Bravo crater, making the southern edge of the Bravo crater the deepest side. Two tests in particular, named Castle Romeo (detonated 1 mo after Bravo) and Hardtack Poplar (detonated in 1958), had yields of ∼10 megatons each, and both were located southwest and approximately 2 km away from the Bravo center. Six more nuclear weapons were detonated in close proximity to the Bravo crater. Nuclear weapons testing at the location of the Bravo crater did not end with the Bravo test.
Ivy Mike was detonated in the northwest rim of Enewetak Atoll 16 mo earlier, on November 1, 1952.
The Bravo bomb was the second large-scale thermonuclear weapon test performed, following the first test, code named Ivy Mike, whose yield was 10.4 megatons.
The test was performed on a strip of land adjacent to Nam Island. The Bravo bomb was the first thermonuclear weapon test using solid LiD material as the central design for the fusion process, allowing this device to be aviation deliverable to enemy targets. The weapon, code-named Castle Bravo, released an energy equivalent to 15 million tons of trinitrotoluene (TNT) (15 megatons), a value substantially larger than the US military’s prior estimates, although controversy still remains on this topic ( 1). On March 1, 1954, the US military detonated its largest thermonuclear weapon on an island located in the northwestern rim of Bikini Atoll in the Marshall Islands.