70-Year Anthropogenic Uranium Imprints of Nuclear Activities in Baltic Sea Sediments

Abstract

Strongly strati ed water structure and densely populated catchment make the Baltic Sea one of the most polluted seas. Understanding its circulation pattern and time scale is essential to predict the dynamics of hypoxia, eutrophication, and pollutants. Anthropogenic 236 U and 233 U have been demonstrated as excellent transient tracers in oceanic studies, but unclear input history and inadequate long-term monitoring records limit their application in the Baltic Sea. From two dated Baltic sediment cores, we obtained high-resolution records of anthropogenic uranium imprints originated from three major human nuclear activities throughout the Atomic Era. Using the novel 233 U/ 236 U signature, we distinguished and quanti ed 236 U inputs from global fallout (43.3%-50.5%), Chernobyl accident (< 0.9%), and discharges of civil nuclear industry (48.6%-56.7%) to the Baltic Sea. We estimated the total release of 233 U (7-15kg) from the atmospheric nuclear weapons testing, and pinpointed 233 U peak signal in the mid-to-late 1950s as a potential time marker for the onset of the Anthropocene Epoch. This work also provides fundamental 236 U data for Chernobyl accident and early discharges from civil nuclear facilities, prompting worldwide 233 U-236 U tracer studies. We anticipate our data to be a broader application in model-observation interdisciplinary research on water circulation and pollutant dynamics in the Baltic Sea.

Developing Accelerator Mass Spectrometry Capabilities for Anthropogenic Radionuclide Analysis to Extend the Set of Oceanographic Tracers

“…The novel data on the 233 U/ 236 U depth profile in an ocean water column presented in Figure 2E presents a weighted mean of (1.04 ± 0.18) × 10 −2 which is slightly lower (more than 1 σ) than the value for global nuclear weapons (1.40 ± 0.15) × 10 −2 fallout published only recently in Hain et al (2020) for the first time. As discussed in this initial publication on anthropogenic 233 U and recently supported by data from Baltic Sea sediments (Lin et al, 2021), tropospheric fallout from smaller 233 U fuelled fission devices might have led to a locally more varying 233 U distribution. Being located west of the relevant Nevada test site, the Pacific Ocean might have received relatively small input from these smaller weapons but large amounts of 236 U have been released at the Pacific Proving Grounds, which could be a possible explanation for the lower 233 U/ 236 U ratios in the presented water column.…”

Understanding Source Terms of Anthropogenic Uranium in the Arctic Ocean – First 236u and 233u Dataset in Barents Sea Sediments

“…Associated with higher particle load and sedimentation rate, a higher areal cumulative inventory of 236 U compared to this work was reported in a sediment core from the Philippine Sea ((2.79 ± 0.20) × 10 12 atom/m 2 ). Up to date, the highest sedimentary 236 U inventory in the range of (3.16-3.53) × 10 13 atom/m 2 was reported for the Baltic Sea (Lin et al, 2021), which was related to the significant input of 236 U from the two European reprocessing plants.…”

“…The integrated 233 U/ 236 U atomic ratio for global fallout signal in the ocean was estimated to be (1.40 ± 0.15) × 10 −2 after the termination of atmospheric nuclear weapons testing in the 1980s (Hain et al, 2020), whereas sources associated with the civil nuclear industry were at the level of 1 × 10 −7 -1 × 10 −6 (HELCOM MORS Discharge database, n.d.; Naegeli, 2004). It should be noted that due to different source inputs between 233 U and 236 U from the atmospheric weapons testing, 233 U/ 236 U atomic ratios higher than the integrated value of (1.40 ± 0.15) × 10 −2 have been reported for global fallout during 1950s-1970s in regional natural archives (Hain et al, 2020;Lin et al, 2021;Qiao et al, 2022).…”

“…The primary sources of anthropogenic 236 U include global fallout (about 900-1400 kg) of atmospheric nuclear weapons testing (Sakaguchi et al, 2009;Steier et al, 2008;Winkler et al, 2012) and discharges (about 250 kg) from the two European nuclear fuel reprocessing plants at Sellafield (SF) and La Hague (LH) (Castrillejo et al, 2020). In addition, releases from nuclear accidents (e.g., Chernobyl accident) (Lin et al, 2021) and local sources (e.g., Studsvik research facility) (Qiao et al, 2021) made minor contributions.…”

“…Very recently, advances in the accelerator mass spectrometry (AMS) technique open up the possibility to determine another anthropogenic uranium isotope 233 U (t ½ = 1.59 × 10 5 y) at environmental levels (Hain et al, 2020). This enables the application of 233 U-236 U pair to identify the origin of 236 U (Hain et al, 2020;Lin et al, 2021;Lin et al, 2022b;Qiao et al, 2022;Qiao et al, 2021;Qiao et al, 2020), because the 233 U/ 236 U ratios, only replying to the burn-up history of the nuclear fuel, are not altered by the biogeochemical processes along the transport pathways.…”