Chronology of Pu isotopes and 236U in an Arctic ice core

The 239Pu nuclear fallout as recorded in an Antarctic ice core drilled at Dome C (East Antarctica)

Starting from 1952 C.E. more than 540 atmospheric nuclear weapons tests (NWT) were conducted in different locations of the Earth. This lead to the injection of about 2.8 t of ²³⁹Pu in the environment, roughly corresponding to a total ²³⁹Pu radioactivity of 6.5 PBq. A semiquantitative ICP-MS method was used to measure this isotope in an ice core drilled in Dome C (East Antarctica). The age scale for the ice core studied in this work was built by searching for well-known volcanic signatures and synchronising these sulfate spikes with established ice core chronologies. The reconstructed plutonium deposition history was compared with previously published NWT records, pointing out an overall agreement. The geographical location of the tests was found to be an important parameter strongly affecting the concentration of ²³⁹Pu on the Antarctic ice sheet. Despite the low yield of the tests conducted in the 1970s, we highlight their important role in the deposition of radioactivity in Antarctica due to the relative closeness of the testing sites.

Historical changes of 236U/238U and 235U/238U isotopic ratios in Tokyo Bay from the 1960s to the 2000s

We examine the historical changes of 236U/238U and 235U/238U in a sediment core collected in Tokyo Bay and elucidate the anthropogenic sources of uranium in the 1960s-2000s. Uranium-236 was detected in samples deposited in the 1960s-2000s, and the 236U/238U ratio of the sediment core shows peak values in the 1970s. The 235U/238U isotopic ratios in samples deposited in the early 1960s are almost identical to that of natural uranium, implying that the 236U might have originated from global fallout. A decrease in 235U/238U was observed in the late 1960s-2000s, suggesting that depleted uranium from nuclear fuel reprocessing increased the 236U/238U ratios in the sediment. The 236U/238U values in sediments from the 1980s-2000s were lower than those in the 1970s but considerably higher than those in the 1960s, suggesting that the main source of depleted uranium still remains around Tokyo Bay. Our results demonstrated that the depleted uranium released in the 1970s should be considered as an important end-member when using uranium isotopic ratios as environmental tracers in closed aquatic environments around industrial cities.

Retrospective determination of fallout radionuclides and 236U/238U, 233U/236U and 240Pu/239Pu atom ratios on air filters from Vienna and Salzburg, Austria

137Cs and 241Pu (via 241Am) concentrations were measured γ-spectrometrically on air filters from the early 1960s (mainly from 1964-66) from Vienna, Austria, and an alpine station in Salzburg, Austria. Accelerator mass spectrometry (AMS) was used to determine 240Pu/239Pu, 236U/238U and 233U/236U atom ratios as well as 236U, 239Pu and 240Pu atom concentrations. The maximum 236U/238U atom ratio of these unique undisturbed global fallout samples was (1.19 ± 0.31) × 10-5 in spring 1964. The 233U/236U atom ratios were found within (0.15-0.49) × 10-2 and indicate that the weapons tests of the early 1960s can be excluded as 233U source. The 236U/239Pu atom ratios were calculated in the range of 0.22-0.48.

A review of anthropogenic radionuclide 236U: Environmental application and analytical advances

²³⁶U is an anthropogenic radionuclide that is produced from nuclear reactions of ²³⁵U(n, γ) and ²³⁸U(n, 3n). It has gained extensive attention in the field of environment, geology, nuclear emergency, and nuclear forensics. Due to the unique physical and chemical character and the distinct fingerprint character from different sources, ²³⁶U has been successfully applied in the environmental tracer, nuclear material source appointment, and environmental assessment. Until now, few reviews were published about the database, application, and the latest analytical technology development of ²³⁶U. In this review, the ²³⁶U concentration and ²³⁶U/²³⁸U isotope ratio were summarized, and the data were classified into four categories, including soil and seawater samples affected by global fallout and nuclear incidents. Furthermore, the development of environmental application and pretreatment methods were also summarized. The advanced pretreatment technology using alkali fusion and flow injection was especially discussed to introduce the development of a rapid analytical method. Finally, the research challenge and direction of ²³⁶U were proposed for further research, such as the tracer application combining ²³⁶U with other radionuclides in the terrestrial environment and the precise analysis of minor isotopes in ultra-trace uranium samples. We hope this review will help scholars to have a deep research on the analysis and application of ²³⁶U.

Retrospective determination of U and Pu isotopes and atom ratios in lung samples from Vienna, Austria

Uranium and plutonium isotope concentrations as well as ²³⁶U/²³⁸U and ²⁴⁰Pu/²³⁹Pu atom ratios were measured by AMS in human lung samples from the early 1960s. The ²³⁶U concentrations as well as the ²³⁶U/²³⁸U atom ratios show a maximum in 1964, ²³⁹Pu and ²⁴⁰Pu concentrations are increasing continually from 1962 to 1965. ²³⁶U/²³⁸U atom ratios are lower by two orders of magnitude compared to corresponding aerosol data from Vienna, probably due to older ²³⁸U deposited in the lungs, enhanced ²³⁸U concentrations in the city air, and activity partition within different particle sizes. The ²³⁶U/²³⁹Pu atom ratios in lung samples are also lower than expected from the aerosol data, while ²⁴⁰Pu/²³⁹Pu atom ratios lie well within the range typical for nuclear bomb fallout.

Unveiling the extreme environmental radioactivity of cryoconite from a Norwegian glacier

This study is a first survey of the occurrence of artificial (¹³⁷Cs, ²⁴¹Am, ²⁰⁷Bi, Pu isotopes) and natural (²¹⁰Pb, ²²⁸Ac, ²¹⁴Bi, ⁴⁰K) radionuclides in Norwegian cryoconite. Cryoconite samples were collected before (12 samples) and after (5 samples) a rainfall event, after which 7 cryoconite holes dissapeared. The concentrations of radionuclides in cryoconite samples from the Blåisen Glacier are compared with data from the Arctic and Alpine glaciers. Cryoconite samples from the studied glacier had extremely high activity concentrations of ¹³⁷Cs, ²⁴¹Am, ²⁰⁷Bi and ^239+240Pu (up to 25,000 Bq/kg, 58 Bq/kg, 13 Bq/kg and 131 Bq/kg, respectively) and also high concentrations of organic matter (OM), comparing to other Scandinavian and Arctic glaciers, reaching up to ~40% of total mass. The outstandingly high concentrations of ¹³⁷Cs, ²⁴¹Am, Pu isotopes, and ²⁰⁷Bi on the Blåisen Glacier are primarily related to bioaccumulation of radionuclides in organic-rich cryoconite and might be enhanced by additional transfers of contamination from the tundra by lemmings during their population peaks. The presumed influence of intense rainfall on radionuclide concentrations in the cryoconite was not confirmed.

Deciphering anthropogenic uranium sources in the equatorial northwest Pacific margin

This work reports the first high-resolution deposition records of anthropogenic uranium (²³⁶U and ²³³U) in a sediment core taken at the continental slope of the Philippine Sea off Mindanao Island in the equatorial northwest Pacific Ocean. Two notable peaks were observed in both profiles of ²³⁶U and ²³³U concentrations, with a narrower peak in 1951-1957 corresponding to close-in Pacific Proving Grounds (PPG) signal, and a broader peak in 1960s-1980s corresponding to the global fallout from nuclear weapons testing. ²³⁶U and ²³³U areal cumulative inventories in the studied sediment core are (2.79 ± 0.20) ∙ 10¹² atom ∙ m^-2 and (3.12 ± 0.41) ∙ 10¹⁰ atom ∙ m^-2, respectively, about 20-30% of reported ²³³U and ²³⁶U inventories from the direct global fallout deposition. The overall ²³³U/²³⁶U atomic ratios obtained in this work vary within (0.3-3.5) ∙ 10^-2, with an integrated ²³³U/²³⁶U atomic ratio of (1.12 ± 0.17) ∙ 10^-2. The contribution from global fallout and close-in PPG fallout to ²³⁶U in the sediment core is estimated to be about 69% and 31%, respectively. We believe the main driving process for anthropogenic uranium deposition in the Philippine sediment is continuous scavenging of dissolved ²³⁶U from the surface seawater by sinking particles.

Isotopic signatures of plutonium and uranium at Bikar atoll, northern Marshall Islands

We present plutonium (Pu) and uranium (U) isotopic fingerprints (or signatures) in environmental samples collected at Bikar Atoll. Bikar is the second -most northern atoll of the Republic of the Marshall Islands, and therefore an important reference point to evaluate the extension of the regional fallout from the Pacific Proving Grounds (PPG) in Bikini and Enewetak Atolls. Previous studies have shown that regional fallout from atmospheric nuclear weapon testing (NWT) in Bikini and Enewetak has resulted in elevated levels of fallout radionuclides in this atoll. In order to optimally interpret the isotopic fingerprints, we compare our results with data obtained in eleven certified reference materials, representing different contamination sources. As well as ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, ²³⁸U and ²³⁵U, this study also encompasses less commonly reported radionuclides such as ²⁴²Pu, ²⁴⁴Pu and ²³⁶U. We show the importance of combining numerous fingerprints for improved assessment of the source of a nuclear contamination. In samples from Bikar, Pu and U isotope ratios were found to vary within narrow ranges. Pu and U fingerprints suggest that regional fallout from the Castle Bravo test in March 1954 was the main source of the contamination. This was further confirmed by two different age dating approaches that estimated 1954 as the year of the contamination. We demonstrate that use of an exponential function to approximate the yield of heavy radionuclides in thermonuclear explosions with increasing mass is a valid approach for estimating the age of a contamination. We show that, if sufficient radionuclide activity concentration measurement results with low uncertainties are available, this method is robust.

First dataset of 236U and 233U around the Greenland coast: A 5-year snapshot (2012-2016)

We report the first combined dataset of ²³⁶U and ²³³U in the Greenland marine environment during the period of 2012-2016. Results are discussed in terms of time evolution and spatial distribution of ²³⁶U concentration, and atomic ratios of ²³⁶U/²³⁸U and ²³³U/²³⁶U. ²³⁶U concentrations along the Greenland coast are distributed within a relatively narrow range of (0.7-12.9) × 10⁷ atom/L, corresponding to ²³⁶U/²³⁸U atomic ratios of (1.1-15.5) × 10^-9. The ²³³U/²³⁶U atomic ratios obtained vary from 0.12 × 10^-2 to 1.16 × 10^-2, with the majority distributed in the range of (0.2-0.7) × 10^-2. We applied ²³³U/²³⁶U and ²³⁶U/²³⁸U atomic ratios in a binary mixing model to identify possible ²³⁶U source terms. The results indicate that anthropogenic ²³⁶U and ²³³U in Greenland surface seawater originated from the direct global fallout (DGF) and the Sellafield and La Hague reprocessing plants (RP) is diluted by a third endmember, mostly likely natural ocean water (NOW), containing marginal ²³⁶U and ²³³U. A preliminary estimation of the source terms of ²³⁶U using ²³³U/²³⁶U atomic ratios indicate that, for both eastern and western Greenland seawater, contributions from global fallout (GF) constitute about 30% of ²³⁶U. The dominating source for ²³⁶U, i.e. 70 %, is associated to reactor ²³⁶U including discharges from RP and local reactor input in the Arctic Ocean.

The 240Pu/239Pu atom ratio in Chinese soils

The ²⁴⁰Pu/²³⁹Pu atom ratio is a very effective tool for the identification of the origin of plutonium (Pu) in the soil environment. We examine a dataset of ²⁴⁰Pu/²³⁹Pu atom ratios determined from surface and core soils at 240 sites across China. The data were compiled from 18 separate literature sources from the last 20 years. For the first time the spatial distribution (3 latitude bands and 7 natural regions) of the weighted average ²⁴⁰Pu/²³⁹Pu atom ratios in Chinese soils is investigated. An area to the West of Xining City, shows a weighted average ²⁴⁰Pu/²³⁹Pu atom ratio of 0.167 ± 0.002, lower than that of average global fallout, which likely arises from the addition of local fallout radionuclides from the Chinese nuclear weapon tests at Lop Nor between 1964 and 1980. The Yumen and Jiuquan areas of Northwest China in particular show evidence of very low ratio material from the Chinese nuclear weapon tests. Excluding the impacted area around the test site the weighted average ²⁴⁰Pu/²³⁹Pu ratio of 0.182 ± 0.002 suggests that global fallout is the main source of Pu in most Chinese soils.

Plutonium fallout reconstructed from an Antarctic Plateau snowpack using inductively coupled plasma sector field mass spectrometry

Anthropogenic plutonium (Pu) in the environment is a result of atmospheric nuclear testing during the second half of the 20th century. In this work, we analyzed a 4-meter deep Antarctic Plateau snowpack characterized by a low snow accumulation rate and negligible snow impurities. These sample conditions enabled us to measure the snowpack Pu fallout by applying inductively coupled plasma sector field mass spectrometry to a few mL of snow melt without purification or preconcentration. Pu concentrations in the reconstructed Pu fallout record for the period after 1956 CE increased and decreased in agreement with past atmospheric nuclear testing. Two peaks and two dips associable with historical events were observed, and the highest peak in 1964(±1) CE approximately coincided with the maximum concentration of non-sea-salt sulfate caused by the Mt. Agung eruption in 1963 CE. Enhanced Pu fallout in the 1970s was attributed the geographical proximity of the Southern Hemispheric nuclear test sites. Our results suggest that by improving the instrumental sensitivity and precision, the potential of the Antarctic ice sheet as an archive of Pu fallout can be further explored and utilized for understanding atmospheric dispersion and for dating ice cores.

First report on global fallout 236U and uranium atom ratios in soils from Hunan Province, China

More nuclear power plants continue to be built in China. Due to its long half-life, radiotoxicity and potential application as an environmental tracer, ²³⁶U is one of the most important artificial radionuclides deserving more study since activity data are important for risk assessment. However, the ultra-trace activity of ²³⁶U and its dilution by natural uranium isotopes make it difficult to distinguish its sources and there are only limited global fallout ²³⁶U data for present in Chinese environmental samples. In order to understand the background levels for uranium isotopes, especially ²³⁶U, and clarify their sources, inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) was applied to analyze uranium isotopes in 48 soil samples from Hunan Province, China. The ²³⁴U, ²³⁵U, ²³⁸U and ²³⁶U concentrations were measured as 9.91-33.7, 0.312-1.43, 6.63-28.7 Bq kg^-1 and (1.61-21.3) × 10⁷ atoms g^-1, while, the ²³⁶U/²³⁸U, ²³⁴U/²³⁸U and ²³⁵U/²³⁸U atom ratios were (0.470-4.91) × 10^-8, (5.10-9.31) × 10^-5, and (7.11-7.82) × 10^-3, respectively. The uranium isotopic fractionation may be due to irrigation of the agricultural lands where the samples were collected. Considering the facts that neither previous nuclear tests nor nuclear accidents had occurred in Hunan Province and the present ²³⁶U/²³⁸U atom ratios were included in the range of global fallout values in other areas, it may be concluded that ²³⁶U in soils from Hunan Province is mainly from global fallout. To the best of the authors' knowledge, the presence of global fallout ²³⁶U in soil samples from China has been confirmed for the first time, and these values may be useful as background data for risk assessment in the future.

Natural and artificial radionuclides in a marine core. First results of 236U in North Atlantic Ocean sediments

There are very few data available of ²³⁶U in marine sediment cores. In this study we present the results from the first oceanic depth profile of ²³⁶U in a sediment core sampled in the North Atlantic Ocean, at the PAP site (4500 m depth, Porcupine Abyssal Plain (PAP) site, 49°0' N, 16°30' W). Additionally, the sediment core was radiologically characterized through the measurement of anthropogenic ¹³⁷Cs, ²³⁹Pu, ²⁴⁰Pu, ¹²⁹I and ¹⁴C and natural ²¹⁰Pb, ⁴⁰K and ²²⁶Ra. The measured ²³⁶U concentrations decrease from about 90·10⁶ at g^-1 at the seafloor down to 0.5·10⁶ at g^-1 at 6 cm depth. They are several orders of magnitude lower than the reported values for soils from the Northern Hemisphere solely influenced by global fallout (i.e. from 2700·10⁶ to 7500·10⁶ at g^-1). ²³⁶U/²³⁸U atom ratios measured are at least three orders of magnitude above the estimated level for the naturally occurring dissolved uranium. The obtained inventories are 1·10¹² at m^-2 for ²³⁶U, 80 Bq m^-2 for ¹³⁷Cs, 45 Bq m^-2 for ^239+240Pu and 2.6·10¹² at m^-2 for ¹²⁹I. Atomic ratios for ²³⁶U/²³⁹Pu, ¹³⁷Cs/²³⁶U and ¹²⁹I/²³⁶U, obtained from the inventories are 0.036, 0.11 and 2.5 respectively. Concentration profiles show mobilization probably due to bioturbation from the abundant detritivore holothurian species living at the PAP site sea-floor. The range of ²³⁶U, ¹³⁷Cs, ^239+240Pu and ¹²⁹I values, inventories and ratios of these anthropogenic radionuclides are more similar to the values due to fall-out than values from a contribution from the Nuclear Fuel Reprocessing Plants dispersed to the south-west of the North Atlantic Ocean. However, signs of an additional source are detected and might be associated to the nuclear wastes dumped on the Eastern North Atlantic Ocean.

Nuclear weapons produced 236U, 239Pu and 240Pu archived in a Porites Lutea coral from Enewetak Atoll

A slice from a Porites Lutea coral core collected inside the Enewetak Atoll lagoon, within 15 km of all major nuclear tests conducted at the atoll, was analysed for ²³⁶U, ²³⁹Pu and ²⁴⁰Pu over the time interval 1952-1964 using a higher time resolution than previously reported for a parallel slice from the same core. In addition two sediment samples from the Koa and Oak craters were analysed. The strong peaks in the concentrations of ²³⁶U and ²³⁹Pu in the testing years are confirmed to be considerably wider than the flushing time of the lagoon. This is likely due to the growth mechanism of the coral. Following the last test in 1958 atom concentrations of both ²³⁶U and ²³⁹Pu decreased from their peak values by more than 95% and showed a seasonal signal thereafter. Between 1959 and 1964 the weighted average of the ²⁴⁰Pu/²³⁹Pu atom ratio is 0.124 ± 0.008 which is similar to that in the lagoon sediments (0.129 ± 0.006) but quite distinct from the global fallout value of ∼0.18. This, and the high ^239,240Pu and ²³⁶U concentrations in the sediments, provides clear evidence that the post-testing signal in the coral is dominated by remobilisation of the isotopes from the lagoon sediments rather than from global fallout.

Variations in Pu isotopic composition in soils from the Spitsbergen (Norway): Three potential pollution sources of the Arctic region

Although the polar regions have not been industrialised, numerous contaminants originating from human activity are detectable in the Arctic environment. This study reports evidence of ²⁴⁰Pu/²³⁹Pu atomic ratios in the tundra and initial soils from different parts of west and central Spitsbergen and recognizes possible environmental inputs of non-global fallout Pu. The average atomic ratio of ²⁴⁰Pu/²³⁹Pu equal to 0.179 (ranging between 0.129 and 0.201) in tundra soils are comparable to the characteristic ratio for global fallout (0.180). However, the ²⁴⁰Pu/²³⁹Pu atomic ratios in the initial soils from proglacial zone of glaciers change within wide range between 0.1281 and 0.234 with the mean value of 0.169. By combining alpha and mass spectrometry, the three-sources model was used to identify the Pu sources in initial soils. Our study indicated that the main source of Pu is nuclear tests and that a second source with lower Pu ratio may come from weapons grade Pu (unexploded weapons grade Pu ie. material from bomb which didn't undergo nuclear explosions for example for security tests). Additionally, we found samples with high ²³⁸Pu/^239+240Pu activity ratios and with typical global fallout ²⁴⁰Pu/²³⁹Pu atomic ratios, which are associated with separate sources of pure ²³⁸Pu from the SNAP-9A satellite burn up in the atmosphere.

Anthropogenic 236U in Danish Seawater: Global Fallout versus Reprocessing Discharge

This work focuses on the occurrence of ²³⁶U in seawater along Danish coasts, which is the sole water-exchange region between the North Sea-Atlantic Ocean and the Baltic Sea. Seawater collected in 2013 and 2014 were analyzed for ²³⁶U (as well as ²³⁸U and ¹³⁷Cs). Our results indicate that ²³⁶U concentrations in Danish seawater are distributed within a relatively narrow range of (3.6-8.2) × 10⁷ atom/L and, to a certain extent, independent of salinity. ²³⁶U/²³⁸U atomic ratios in Danish seawater are more than 4 times higher than the estimated global fallout value of 1× 10^-9. The levels of ²³⁶U/²³⁸U atomic ratios obtained are comparable to those reported for the open North Sea and much higher than several other open oceans worldwide. This indicates that besides the global fallout input, the discharges from the two major European nuclear reprocessing plants are dominating sources of ²³⁶U in Danish seawater. However, unexpectedly high ²³⁶U/²³⁸U ratios as well as high ²³⁶U concentrations were observed at low-salinity locations of the Baltic Sea. While this feature might be interpreted as a clue for another significant ²³⁶U input in the Baltic Sea, it may also be caused by the complexity of water currents or slow turnover rate.

Radioactively contaminated areas: Bioindicator species and biomarkers of effect in an early warning scheme for a preliminary risk assessment

Concerns about the impacts on public health and on the natural environment have been raised regarding the full range of operational activities related to uranium mining and the rest of the nuclear fuel cycle (including nuclear accidents), nuclear tests and depleted uranium from military ammunitions. However, the environmental impacts of such activities, as well as their ecotoxicological/toxicological profile, are still poorly studied. Herein, it is discussed if organisms can be used as bioindicators of human health effects, posed by lifetime exposure to radioactively contaminated areas. To do so, information was gathered from several studies performed on vertebrates, invertebrate species and humans, living in these contaminated areas. The retrieved information was compared, to determine which are the most used bioindicators and biomarkers and also the similarities between human and non-human biota responses. The data evaluated are used to support the proposal for an early warning scheme, based on bioindicator species and on the most sensitive and commonly shared biomarkers, to perform a screening evaluation of radioactively contaminated sites. This scheme could be used to support decision-making for a deeper evaluation of risks to human health, making it possible to screen a large number of areas, without disturbing and alarming local populations.

Accumulation of atmospheric radionuclides and heavy metals in cryoconite holes on an Arctic glacier

Surface of glaciers is covered by mineral and organic dust, together with microorganisms forming cryoconite granules. Despite fact that glaciers and ice sheets constitute significance part of land surface, reservoir of freshwater, and sites of high biological production, the knowledge on the cryoconite granules still remain unsatisfactory. This study presents information on radionuclide and heavy metal contents in cryoconites. Cryoconites collected from the Hans Glacier in SW Spitsbergen reveal high activity concentrations of anthropogenic ((238,239,240)Pu, (137)Cs, (90)Sr) and natural ((210)Pb) radionuclides. The (238)Pu/(239+240)Pu activity ratios in these cryoconites significantly exceed the mean global fallout ratio (0.025). The (238)Pu/(239+240)Pu ranged from 0.064 to 0.118. The (239+240)Pu/(137)Cs varied from 0.011 ± 0.003 to 0.030 ± 0.007. Such activity ratios as observed in these cryoconites were significantly higher than the values characterizing global fallout, pointing to possible contributions of these radionuclides from other sources. Heavy metals (Pb, Cd, Cu, Zn, Fe, and Mn) in cryoconites exceed both UCC concentrations and local rocks' concentrations, particularly for cadmium. The concentration ratios of stable lead isotopes ((206)Pb/(207)Pb, (208)Pb/(206)Pb) were determined to discriminate between the natural and anthropogenic sources of Pb in cryoconites and to confirm the strong anthropogenic contribution to heavy metal deposition in the Arctic. In investigated cryoconite holes, two groups of invertebrates, both extremophiles, Tardigrada and Rotifera were detected. Our study indicate that cryoconites are aggregates of mineral and organic substances on surfaces of glaciers are able to accumulate large amounts of airborne pollutants bound to extracellular polymeric substances secreted by microorganisms.

A Method for Continuous (239)Pu Determinations in Arctic and Antarctic Ice Cores

Atmospheric nuclear weapons testing (NWT) resulted in the injection of plutonium (Pu) into the atmosphere and subsequent global deposition. We present a new method for continuous semiquantitative measurement of (239)Pu in ice cores, which was used to develop annual records of fallout from NWT in ten ice cores from Greenland and Antarctica. The (239)Pu was measured directly using an inductively coupled plasma-sector field mass spectrometer, thereby reducing analysis time and increasing depth-resolution with respect to previous methods. To validate this method, we compared our one year averaged results to published (239)Pu records and other records of NWT. The (239)Pu profiles from the Arctic ice cores reflected global trends in NWT and were in agreement with discrete Pu profiles from lower latitude ice cores. The (239)Pu measurements in the Antarctic ice cores tracked low latitude NWT, consistent with previously published discrete records from Antarctica. Advantages of the continuous (239)Pu measurement method are (1) reduced sample preparation and analysis time; (2) no requirement for additional ice samples for NWT fallout determinations; (3) measurements are exactly coregistered with all other chemical, elemental, isotopic, and gas measurements from the continuous analytical system; and (4) the long half-life means the (239)Pu record is stable through time.