240Pu/239Pu signatures allow refining the chronology of radionuclide fallout in South America

Chaboche, Pierre-Alexis; Pointurier, Fabien; Sabatier, Pierre; Foucher, Anthony; Tiecher, Tales; Minella, Jean; Tassano, Marcos; Hubert, Amélie; Morera, Sergio; Guédron, Stéphane; Ardois, Christophe; Boulet, B.; Cossonnet, C.; Cabral, Pablo; Cabrera, Mirel; Chalar, Guillermo; Evrard, Olivier

doi:10.1016/j.scitotenv.2022.156943

Cited by 9 publications

(5 citation statements)

References 35 publications

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“…The characteristic peak typically associated with the maximum 137 Cs bomb fallout (1964)(1965) in South-America 24 ) was logically not observed in this recent sediment sequence (Fig. 3a) in agreement with previous plutonium isotope measurements performed on this core, which demonstrated that sediment deposited well after this period 25 .…”

Section: Core Description and Chronologysupporting

confidence: 90%

Inexorable land degradation due to agriculture expansion in South American Pampa

et al. 2023

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From 1985 onwards, South America has undergone a major expansion of agriculture at the expense of native vegetation (e.g. native Pampa grassland). As an emblematic crop, the surface area cultivated with soybeans has increased by 1000% between 1990 and 2020 in Uruguay. The environmental consequences of this massive land use conversion on soil degradation remain poorly documented although the agriculture expansion is projected to continue to increase in the coming years in South America. In this study, sediment cores were collected in reservoirs located downstream of two contrasted agricultural catchments draining the Rio Negro River (Uruguay) for reconstructing the sediment dynamics and the sources of erosion associated with this expansion.Results demonstrated the occurrence of two periods of acceleration of sediment delivery since the 1980s. The first period of acceleration was recorded in the mid-1990s and was related to afforestation programs. The second and larger acceleration phase was recorded after 2000 during the soybean crop expansion. This period has been marked by a greater supply of sediment from the native grassland source highlighting the impact of agriculture expansion at the expense of native vegetation. Conservation measures should therefore be urgently taken to preserve biodiversity and soil functions in this region.

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Section: Core Description and Chronologysupporting

confidence: 90%

Inexorable land degradation due to agriculture expansion in South American Pampa

et al. 2023

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“…In the southern hemisphere, the horizon of first appearance of 137 Cs in the sediment profile dates that horizon between 1954 and 1956, the exact time being a function of the sediment mean particle size, measurement sensitivity, and the core-section thickness (Leslie and Hancock 2008 ). Due to the low levels of fallout in the southern hemisphere, and the finite time taken to transport sediment-bound 137 Cs from the catchment to its deposition site, the period of peak fallout (1965) is seldom seen in the sediment record south of the equator (Chaboche et al 2022 ). Nevertheless, we prefer to accept the dates ranging between 1954 and 1956 that had been obtained by Leslie and Hancock ( 2008 ) as well as Hancock et al ( 2011 ) since our work and those cited were carried out in Australia and on Australian sediments.…”

Section: Methodsmentioning

confidence: 99%

The effect of the introduction of livestock on the erosion of alpine soils: a comparison of five dating techniques applied to sediments of the Australian alpine Blue Lake

et al. 2023

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Abstract210Pb and 137Cs dating of bulk sediments obtained from the alpine Blue Lake, located in the Snowy Mountains of southeastern Australia, was applied here to date recent lacustrine sediments. In addition, the presence of Pinus pollen (a taxon introduced in Australia about 150 years ago) down to a sediment depth of 56 cm in the core is used to obtain a chronology for the upper part of the core. Accelerated Mass Spectrometry radiocarbon dates obtained from organic muds from the same core do not agree with the chronology constructed using the three other dating techniques. In addition, optically stimulated luminescence (OSL) dating of single quartz grains, from sediment-core samples collected from the same lake, was applied to date recent lacustrine sediments. The optical age of 185 ± 20 years for a sample at 60–62 cm depth, and 470 ± 50 years at 116–118 cm depth are well over 1000 years younger than the ages inferred from radiocarbon dates. We therefore infer that the ‘old’ radiocarbon ages result from carbon stored for considerable time within the catchment prior to its transport and deposition on the lake floor. As plant decomposition occurs at much slower rates in high altitude environments, these results bring into question the veracity of previously published radiocarbon dates from Blue Lake and alpine lake sediments in general. The deposition ages inferred from the 210Pb-137Cs and OSL dating, and the first appearance of Pinus pollen, indicate that for the 100-year period after European settlement (from the mid 1800s to early 1900s) the sediment-accumulation rate increased by a factor of about 2, from 0.19 ± 0.01 cm yr−1 to 0.35 ± 0.02 cm yr−1. In the 1900s the accumulation rate increased further to 0.60 cm yr−1. The accumulation rate was particularly rapid in the 20-year period from 1940–1960, reaching a rate 18 times higher than the pre-European rate in the mid-1950s. The increase in sedimentation rate is attributed to changes in land use resulting from European activities in the lake catchment, primarily through sheep and cattle grazing in the Blue Lake catchment.

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“…Plutonium isotopes reveal that the signature of artificial radioactivity in cryoconite is consistent with a mix of fallout originating from the global stratospheric reservoir and weapons-grade plutonium (Figure 6a). The reference 240 Pu/ 239 Pu ratio for global fallout is 0.18, 61 while Flade Isblink cryoconite exhibits a mean value of 0.15 with a standard deviation of 0.02. Such values point to an excess of 239 Pu, the primary fissile fuel used in nuclear and thermonuclear weapons.…”

Section: Comparison Between Cryoconite and Localmentioning

confidence: 96%

Accumulation of Environmental Radioactivity on the Surface of a High Arctic Ice Cap (Flade Isblink, NE Greenland)

Beard,

Baccolo,

Clason

et al. 2024

Environ. Sci. Technol.

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Under climatic warming, glaciers are becoming a secondary source of atmospheric contaminants originally released into the environment decades ago. This phenomenon has been well-documented for glaciers near emission sources. However, less is known about polar ice sheets and ice caps. Radionuclides are one of the contaminants that can be remobilised through ice melting and accumulate in cryoconite material on the surface of glaciers. To understand the cycling of radionuclides in polar glacial contexts, we evaluate the radioactivity of cryoconite samples from Flade Isblink, a High Arctic ice cap in northeast Greenland. The measured radioactivity is among the highest reported across the High Arctic and the highest from Greenland. The high variability observed among the samples is explained by considering the different macroscopic features of single cryoconite deposits. The radioactivity source is compatible with the stratospheric reservoir established during atmospheric nuclear tests and with weapons-grade fissile fuel, likely originating from Novaya Zemlya proving grounds. This study shows that the ability of cryoconite to accumulate radioactivity in remote areas is undisputed, highlighting the need for a deeper understanding of the remobilisation of radioactive species in polar glacial contexts.

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240Pu/239Pu signatures allow refining the chronology of radionuclide fallout in South America

Cited by 9 publications

References 35 publications

Inexorable land degradation due to agriculture expansion in South American Pampa

Inexorable land degradation due to agriculture expansion in South American Pampa

The effect of the introduction of livestock on the erosion of alpine soils: a comparison of five dating techniques applied to sediments of the Australian alpine Blue Lake

Accumulation of Environmental Radioactivity on the Surface of a High Arctic Ice Cap (Flade Isblink, NE Greenland)

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