A historical record of the impact of nuclear activities based on 129I in coral cores in Baler, Philippines: An update

Anthropocene 129I Record in the Yellow Sea Sediments and Its Indication for River-Delivered Radioactive Pollution to Marginal Seas

As the number of coastal nuclear facilities rapidly increases and the wastewater from the Fukushima Nuclear Plant has been discharged into the Pacific Ocean, the nuclear environmental safety of China's marginal seas is gaining increased attention along with the heightened potential risk of nuclear accidents. However, insufficient work limits our understanding of the impact of human nuclear activities on the Yellow Sea (YS) and the assessment of their environmental process. This study first reports the 129I and 127I records of posthuman nuclear activities in the two YS sediments. Source identification of anthropogenic 129I reveals that, in addition to the gaseous 129I release and re-emission of oceanic 129I discharged from the European Nuclear Fuel Reprocessing Plants (NFRPs), the Chinese nuclear weapons testing fallout along with the global fallout is an additional 129I input for the continental shelf of the YS. The 129I/127I atomic ratios in the North YS (NYS) sediment are significantly higher than those in the other adjacent coastal areas, attributed to the significant riverine input of particulate 129I by the Yellow River. Furthermore, we found a remarkable 129I latitudinal disparity in the sediments than those in the seawaters in the various China seas, revealing that sediments in China's marginal seas already received a huge anthropogenic 129I from terrigenous sources via rivers and thus became a significant sink of anthropogenic 129I. This study broadens an insight into the potential impacts of terrigenous anthropogenic pollution on the Chinese coastal marine radioactive ecosystem.

Plutonium isotopes in the North Western Pacific sediments coupled with radiocarbon in corals recording precise timing of the Anthropocene

Plutonium (Pu) has been used as a mid-twentieth century time-marker in various geological archives as a result of atmospheric nuclear tests mainly conducted in 1950s. Advancement of analytical techniques allows us to measure ²³⁹Pu and ²⁴⁰Pu more accurately and can thereby reconstruct the Pacific Pu signal that originated from the former Pacific Proving Grounds (PPG) in the Marshall Islands. Here, we propose a novel method that couples annual banded reef building corals and nearshore anoxic marine sediments to provide a marker to precisely determine the start of the nuclear era which is known as a part of the Anthropocene. We demonstrate the efficacy of the methods using sediment obtained from Beppu Bay, Japan, and a coral from Ishigaki Island, Japan. The sedimentary records show a clear Pu increase from 1950, peaking during the 1960s, and then showing a sharp decline during the 1970s. However, a constantly higher isotope ratio between ²³⁹Pu and ²⁴⁰Pu suggest an additional contribution other than global fallout via ocean currents. Furthermore, single elevations in ²⁴⁰Pu/²³⁹Pu provide supportive evidence of close-in-fallout similar to previous studies. Coral skeletal radiocarbon displays a clear timing with the signatures supporting the reliability of the Beppu Bay sediments as archives and demonstrates the strength of this method to capture potential Anthropocene signatures.

129I/127I and Δ14C records in a modern coral from Rowley Shoals off northwestern Australia reflect the 20th-century human nuclear activities and ocean/atmosphere circulations

Radionuclides produced by 20th-century human nuclear activities from 1945 (e.g., atmospheric nuclear explosions and nuclear-fuel reprocessing) made significant impacts on earth's surface environments. Long-lived shallow-water corals living in tropical/subtropical seas incorporate the anthropogenically-produced radionuclides, including ¹²⁹I and ¹⁴C, into their skeletons, and provide time series records of the impacts of nuclear activities. Here, we present ¹²⁹I/¹²⁷I and Δ¹⁴C time series records of an annually-banded modern coral skeleton from Rowley Shoals, off the northwestern coast of Australia, in the far eastern Indian Ocean. The ¹²⁹I/¹²⁷I and Δ¹⁴C records, covering the period 1930s-1990s, exhibit distinct increases caused by the nuclear activities, and their increasing profiles are clearly different from each other. The first distinct ¹²⁹I/¹²⁷I increase occurs from 1955 to 1959, followed by a decrease in 1960-1963. The increase is probably due to US atmospheric nuclear explosions in Bikini and Eniwetok Atolls in 1954, 1956 and 1958. The ¹²⁹I produced in those nuclear tests would be transported by the North Equatorial Current, a portion of which passes through the Indonesian Throughflow and then reaches Rowley Shoals. This initial increase from 1955 is, however, absent in the Δ¹⁴C record, which shows a distinct increase from 1959 and its peak around the mid-1970s, followed by a gradual decrease. This absence and the 4-year-delayed Δ¹⁴C increase are likely due to dilution of explosion-produced ¹⁴C with natural carbon (by seawater mixing and air-sea gas exchange) being much more intense than that of explosion-produced ¹²⁹I with natural iodine (by the same processes), suggesting that the ¹²⁹I/¹²⁷I ratio is a more conservative anthropogenic tracer in surface ocean waters, as compared to Δ¹⁴C. The second ¹²⁹I/¹²⁷I increase is contemporaneous with a rapid Δ¹⁴C increase during 1964-1967, followed by a rapid ¹²⁹I/¹²⁷I decrease in 1968-1969; the increases can be ascribed to very large atmospheric nuclear explosions conducted in the former Soviet Union in 1961-1962. The third ¹²⁹I/¹²⁷I increase appears between 1969/1970 and 1992, which can be attributed to airborne ¹²⁹I released from nuclear-fuel reprocessing facilities in Europe, the former Soviet Union and the US. The coral ¹²⁹I/¹²⁷I and Δ¹⁴C time series records, combined with previous studies, enhance our understanding of the behavior of anthropogenic ¹²⁹I and ¹⁴C in the global ocean and atmosphere.

3D X-ray computed tomography gray value and age model datasets of coral cores Baler 2 and 3 (Philippines)

The datasets here contain the 3D X-ray computed tomography (3DXCT) gray values and age models of coral cores Baler 2 and 3, taken from Baler, Aurora, Philippines. 3DXCT was used to analyze 5 mm-thick slabs of the coral cores. From the resulting 3DXCT images, gray values were determined per pixel from top to bottom of the slabs. The gray value profiles across the length of the slabs were then matched with records of sea surface temperature (SST) of the Baler site to construct the age model of the coral cores. Daily SST records from October 2018 to February 1982 were from the Optimum Interpolation Sea Surface Temperature or OISST [1,2], while monthly SST records from February 1982 to May 1945 were from the Extended Reconstructed Sea Surface Temperature or ERSST [3]. The gray value datasets of coral cores Baler 2 and 3 present historical records of the corals' response to changing environments through the years and may be used in studies related to such. An example of this can be seen in the relationship between coral gray values and SST. Furthermore, the age model datasets of Baler 2 and 3 serve as the basis for interpretation for all current and future studies on these coral cores. These datasets were originally produced for the research work titled “A historical record of the impact of nuclear activities based on ¹²⁹I in coral cores in Baler, Philippines: an update” [4].