In the 1950s, U.S. nuclear tests were conducted at Bikini and Enewetak; decades later, Guam corals preserved carbon-14 spikes linked to tests in 1954, 1956, and 1958

In the 1950s, U.S. nuclear tests were conducted at Bikini and Enewetak; decades later, Guam corals preserved carbon-14 spikes linked to tests in 1954, 1956, and 1958SynopsisGuam’s coral reefs act as natural historians, chronicling chemical footprints of Cold War-era nuclear tests. Distinct radiocarbon spikes from the years 1954, 1956, and 1958 reveal the pathways of nuclear fallout as it spread through the tropical Pacific. This invaluable information extracted from coral cores charts a sixty-year timeline of the ocean’s chemical changes, enabling scientists to accurately date marine species currently inhabiting these waters.Listen to this article in summarized formatPacific coral reefs. Image Credit: Wikimedia CommonsBeneath Guam's coastal waters, centuries-old coral reefs hold a chemical record of the Cold War's most powerful nuclear tests. NOAA Fisheries scientists examined the reefs and found chemical spikes from 1954, 1956, and 1958, the years the U.S. detonated its largest thermonuclear devices at Bikini and Enewetak atolls in the Pacific Proving Grounds, according to a 2016 study by NOAA researcher Allen H. Andrews published in the Journal of Geophysical Research: Oceans.Uncovering history buried in Pacific coral reefsThe mid-20th century marked an unprecedented era of atmospheric nuclear testing in the Marshall Islands, located roughly 1,200 miles east of Guam. As these massive detonations vaporized coral reefs and superheated the surrounding air, they released intense neutrons that created high concentrations of radiocarbon. While scientists knew that atmospheric testing dispersed radioactive isotopes across the globe, understanding how those particles traveled through oceanic pathways remained uncertain. Analyzing the coral core gave researchers an unusually detailed, high-resolution record, one NOAA describes as unmatched in magnitude and resolution among Indo-Pacific coral cores, of how nuclear fallout moved through the tropical Pacific.Guam's coral cores are part of an event that scientists refer to as the "bomb pulse." Atmospheric nuclear testing in the 1950s and early 1960s released enough radiocarbon to raise global atmospheric levels, not just levels near the test sites, according to NOAA researchers who have studied the phenomenon. This rise in radiocarbon left a detectable signal in tree rings and ocean sediments that persists today. Researchers working in fields such as forensic science and art authentication have used this same radiocarbon increase to determine when a biological sample formed or when an object was made. Guam's coral reefs show a detailed version of the same global signal.​How corals store radiocarbonThis natural tracking method is based on coral features. Coral species called Porites build skeletons that are made of calcium carbonate. These skeletons get their dissolved carbon from the seawater. When the fireballs exploded at Bikini and Enewetak atolls, the extreme heat broke down the reef structure into tiny pieces of carbonates. These pieces absorbed carbon-14 before sinking into the ocean.The calcium-carbonate skeleton of Porites lobata. Image Credit: Wikimedia CommonsThe three distinct atomic test spikesThree separate radiocarbon spikes have been noted in the coral core extracted from Guam. These correspond to specific nuclear operations that increased marine radiocarbon values above background levels. Operation Castle in 1954 caused the largest increase in marine radiocarbon values, a spike of about 700% (parts per thousand) above pre-bomb levels. A follow-up assay with finer resolution later revised this peak upward to roughly 300% above the surrounding trend. Operation Redwing in 1956 caused the smallest of the three increases, with radiocarbon values rising by about 35% above the trend. Operation Hardtack I in 1958 caused the third spike, occurring during 1958–59. Radiocarbon values rose by about 70% above the background trend, roughly double Redwing's spike, but far smaller than Castle's.The record's full sixty-year spanThe finding mattered not only because of the three individual spikes, but because one coral sample contained three chemically distinct markers linked to three separate nuclear operations. A closer look at the same data later revealed additional structure in the first (1954) peak that wasn't captured in the original measurement, suggesting the core holds more detail than initially reported.The Castle Bravo thermonuclear test at Bikini Atoll in 1954. Image Credit: WikipediaThe period covered in this dataset extends well beyond the bomb-testing period. According to the NOAA Fisheries InPort record, the usable time frame of the radiocarbon concentration in this coral covers 1939 to 2000, providing a roughly six-decade record of the ocean's chemical state before, during, and after those tests. The full dataset, available from the NOAA National Centers for Environmental Information, allows researchers to compare radiocarbon concentrations before and after the tests. That long-term view is what gives the record its lasting value: scientists still use it today to determine the true age of marine species, including reef fish and giant clams. It enables comparison of radiocarbon concentrations before and after the events. Such long-term data is crucial to the record's significance, as it is used today to determine the true age of marine species, including reef fish and giant clams.Ocean transport dynamics and modern research valueThese sudden, intense peaks were unusual because typical marine bomb-radiocarbon signals enter surface waters slowly through air-sea gas diffusion, producing a more gradual curve. However, the rapid entry of these Guam peaks confirmed that they were fallout from pulverized coral material moving through fast oceanographic currents. The dataset's NOAA record shows that ocean surface currents carried these radiotracers to Guam.What the coral records showMarine biologists have used these radiocarbon markers mainly to validate the ages of long-lived reef species. The pronounced spike in the 1950s can serve as a marker for calculating the age and growth rate of marine life, ocean currents, and climatic variations.( Originally published on Aug 22, 2026 )Read More News on(Catch all the US News, UK News, Canada News, International Breaking News Events, and Latest News Updates on The Economic Times.) Download The Economic Times News App to get Daily International News Updates....moreless