Anthropogenic 129I Research Articles

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.

Anthropogenic iodine-129 tracks iodine cycling in the Arctic

Global warming has accelerated the iodine cycle in the Arctic Ocean, amplifying its significance in the global iodine cycle. However, some intricacies of the iodine cycle in the Arctic marine environment remain unclear. In this study, we present concentrations of stable- and radio-iodine (127I and 129I) in total iodine, iodide (I–), and iodate (IO3–) in seawater from the Beaufort, Chukchi, and Bering Seas. Results show a wide range of 129I/127I ratios of total iodine (3.2 × 10–12–9.3 × 10–9), indicating that the total 129I/127I ratio is a valuable fingerprint for identifying water masses and comprehending mixing processes. Iodine loss in surface seawater was quantitatively assessed using 129I, revealing that Arctic rivers substantially contribute to the emission of iodine into the atmosphere from the Arctic and subarctic seas. Our redox simulation in the Arctic intermediate layer shows the concentrations and 129I/127I ratios of I– and IO3– during its migration and provides the first evidence of an IO3– reduction process masked by the I– oxidation in the intermediate Arctic Ocean. Oxidation and reduction processes in the intermediate Arctic Ocean were characterized by extremely slow rates, at 0.95–2.41 and 0.26 ± 0.13 nM/year, respectively. Our findings demonstrate the effectiveness of anthropogenic 129I in tracking iodine cycling in the Arctic marine environment.

Reconstructing atmospheric 129I deposition over 170 years with the varved sediment in the Sihailongwan Maar Lake, northeast China

Long-term deposition of atmospheric radioactive iodine-129 (129I) is important for assessing the impact of human nuclear activities (HNAs), but still not well understood in East Asia. In this study, we quantitatively reconstructed the deposition history of airborne 129I using varved sediment from Sihailongwan Maar Lake (SHLW) in northeast China. Our results revealed significant increases in 129I concentrations and 129I/127I atomic ratios since the 1950s, indicating the influence of HNAs on the environment and marking the onset of the Anthropocene. The variation of 129I in the investigated site can be primarily attributed to the global fallout of ANWT as well as nuclear fuel reprocessing in Europe, Russia and the USA. Notably, neither the Chernobyl nor the Fukushima nuclear accidents have had any discernable impact on the SHLW Lake. Over the past 170 years (1846–2021), the reconstructed fluxes indicate a rapid increase in 129I deposition from the early 1950s until the 1970s followed by dramatic changes thereafter. The measured 129I fluxes range between (1.26–349) × 109 atoms m−2 yr−1 in the SHLW Lake, which are consistent with similar latitude zones across East Asia, but differ significantly from those observed in high-elevation glaciers within the Northern Hemisphere due to prevailing atmospheric circulation patterns. The total 129I inventory was calculated to be 11.9 × 1012 atoms m−2, with natural and anthropogenic 129I accounting for 2.86 % and 97.1 %, respectively, suggesting an overwhelming artificial contribution. The reconstructed fluxes and inventory of atmospheric 129I deposition quantitatively distinguish the natural and artificial contributions, and provide a novel insight into the historical environmental impact of HNAs in East Asia and the characteristics of the Anthropocene.

Sources of highly regional 129I in soils in northeast China

The transport and deposition pathways of anthropogenic radionuclides at the global scale, particularly volatile 129I, remain somewhat elusive due to a dearth of comprehensive investigations. To gain a better understanding of the transport dynamics and deposition mechanism of anthropogenic 129I in the terrestrial environment, one hundred surface soil samples collected from northeast China were analyzed for 129I and 127I concentrations in this study. Our findings reveal that 129I/127I atomic ratios in the mid-eastern Inner Mongolia (MIM) were approximately an order of magnitude higher than the rest of the investigated area. This is, besides the global fallout and the long-range transport of 129I released from the European nuclear reprocessing plants via westerly winds, possibly attributed to the dust with high 129I levels from the East Asian arid regions. In addition to the significant dust-induced 129I input, the unique meteorological conditions and topographical features in the MIM synergistically contribute to the pronounced accumulation and deposition of 129I in this region. This study will provide novel insights into the transport and deposition mechanism of anthropogenic radionuclides, which is significant for the assessment of anthropogenic nuclear activities on the environment in the future.

Reconstruction of the Sources and Their Contributions to 129I in Northern Xinjiang, China.

Anthropogenic 129I, as a long-lived fission product and volatile radionuclide, can be used to investigate dispersion of air masses and the deposition of atmospheric pollution. Surface soil and soil core samples were collected from Northern Xinjiang and analyzed for 127I and 129I. The results show that 129I/127I atomic ratios in surface soil are inhomogeneous with a range of (2.07-106) × 10-9, and the maximum values in each soil core occurred at surface-subsurface layers (0-15 cm) at undisturbed sites. The dominant source of 129I in Northern Xinjiang is European nuclear fuel reprocessing plant (NFRP) releases, accounting for at least 70% of the total inventory; less than 20% of 129I originates from the global fallout of atmospheric nuclear weapons tests; less than 10% comes from the regional deposition of nuclear weapons tests at the Semipalatinsk site; and the regional deposition from the nuclear weapons tests at the Lop Nor site is insignificant. The European NFRP-derived 129I was transported to Northern Xinjiang via long-distance atmospheric dispersion with the westerlies through Northern Eurasia. The distribution of 129I in the surface soil in Northern Xinjiang is mainly controlled by topography, wind fields, land utilization, and vegetation coverage.

Spatial variation and species transformation of 129I and 127I in the Central Arctic Ocean

The spatial distributions of anthropogenic 129I and natural 127I in iodide (I−) and iodate (IO3−) of anthropogenic 129I and natural 127I were investigated in the upper central Arctic Ocean. The results show that the molecular ratios of reductive iodide (I−) to oxidative iodate (IO3−) ranged from 0.228 to 0.560 for 127I and 0.383 to 0.827 for 129I in the Polar Mixed Layer (PML). Greater 127I− concentrations and markedly higher I−/IO3− ratios for both 129I and 127I were found in the PML over the Lomonosov and Alpha Ridges. This suggests that the in-situ formation of I− occurs as a result of enhanced reductive environments at these locations due to bacterial-mediated decomposition of dissolved organic matter (DOM) that likely originates from the inflow of river water into the central Arctic Ocean. Ratios of 129I−/129IO3− and 127I−/127IO3− decrease gradually along the main transport pathway of the Atlantic water, revealing that I− is gradually oxidized back to IO3− at a slow net rate within the Atlantic Water Layer. Our study provides insights into the marine geochemical cycling of iodine and raises the potential for iodine species, notably of 129I, to be used as indicators of changes in the redox condition of surface water in the Arctic Ocean, which may occur due to the predicted impacts of climate change.

Iodine cycling in the subarctic Pacific Ocean: Insights from 129I

As the largest iodine reservoir on the Earth’s surface, the ocean plays a vital role in global iodine cycling. Here, we present results on concentrations of stable- and radio-iodine (127I and 129I) of total iodine (TI), iodide (I–), and iodate (IO3–) in seawater samples collected in the top 800 m of the subarctic Pacific Ocean. The speciation distributions of both 127I and 129I showed large variations in depth and geographical location. The T127I concentrations ranged from 321 to 484 nM, were lower at the surface, and increased with depth. In all depth profiles of T129I, the maximum concentrations occurred in the subsurface layer, below which, the T129I concentrations decreased with depth and ranged from 0.2 to 2.1 × 107 atoms/L. Besides, the 129I/127I atom ratios in iodide were significantly higher than those in iodate. It can be inferred from existing research that anthropogenic 129I from atmospheric deposition is the overwhelming source of 129I in the subarctic Pacific Ocean. On this basis, we successfully simulated the 129I vertical dispersion using a one-dimensional vertical diffusion model. The unbalanced distribution of 129I among different iodine species provided useful information for demonstrating the inevitability of the oxidation process of iodide in nature, although whether this oxidation occurred in the ocean remains to be further explored, and the indispensable contribution of iodate to the iodine removal processes in the upper ocean. Our study suggests that anthropogenic 129I can be used as an effective intrinsic tracer for the study of iodine cycling.

Anthropogenic 129I in seawaters along the north-central part of the English Channel: Levels and tracer applications

Anthropogenic 129I in seawaters along the north-central part of the English Channel: Levels and tracer applications

Water mass composition in Fram Strait determined from the combination of 129I and 236U: Changes between 2016, 2018, and 2019

Changes in the provenance and composition of waters exported from the Arctic Ocean have the potential to impact large-scale ocean circulation processes in the sub-polar North Atlantic. The main conveyor of waters from the Arctic Ocean to lower latitudes is the East Greenland Current (EGC), flowing southward through Fram Strait. It is therefore crucial to determine and monitor the composition of the EGC, a mixture of polar waters of different origins. Here we present a pilot study on the potential of the long-lived anthropogenic radionuclides 129I and 236U as tracers of the EGC water mass composition, based on a time series of 236U and 129I concentrations measured across Fram Strait in the years 2016, 2018, and 2019. The overall spatial distribution of 236U and 129I was similar among the three sampling years, but a decrease in concentration was observed in the upper water column of the EGC. The observed changes could only partly be attributed to the transient nature of the radionuclide signals, but instead pointed to changes in the EGC water mass composition. To investigate these changes, 236U and 129I were first combined in a mixing model featuring the endmembers expected in the upper EGC. We distinguished between Pacific Water (PAC), Atlantic Water advected from the Arctic Ocean (ATL), and Atlantic Water recirculating in Fram Strait (RAC). In 236U-129I tracer space, PAC and RAC showed similar tracer signatures, but were well distinguished from ATL. From 2016 to 2018/19, a decrease in the ATL fraction was evident for the upper EGC. Secondly, the respective combination of 236U and 129I with salinity showed differences in absolute water mass fractions, but similar temporal trends. Both suggested an increase in PAC of about 20% for the uppermost layer of the EGC (samples with potential densities below 26.5) and an increase in RAC of about 10−20 % for denser samples. 129I and 236U, in combination with salinity, were shown to be suitable tracers to investigate water mass composition in Fram Strait, with the advantage that they can distinguish Atlantic Water advected from the Arctic Ocean from that recirculating in Fram Strait.

Distribution of Anthropogenic 129I in the Western South China Sea and Its Application for Tracing the Sources and Movement of Pollution.

Anthropogenic 129I has been dispersed all over the world and could be utilized as an oceanographic tracer based on its conservative nature in the ocean. The first datasets of 129I and 127I were obtained by analysis of seawater of 36 water columns collected in the western South China Sea during August-September 2018. The measured 129I concentrations decreased with depth from (0.93-1.61) × 107 atoms/L in the upper 200 m to (0.04-0.14) × 107 atoms/L at 1500 m, indicating a clear anthropogenic source in the upper layer, mainly originated from the global fallout. The riverine input of the deposited 129I on the catchment area of the Mekong River is an important source besides the direct deposition in the seas. The water mass with high 129I from the Mekong River water moves to the east at 11°N by the North Nansha Current in the surface layer (2-25 m). The exponentially decreasing 129I level with depth indicates that the vertical dispersion of 129I from the upper to the lower layer was mainly through slow diffusion, and the deep water at more than 1500 m was not significantly contaminated by the upper layer water at least in the past 70 years.

Ultra-Sensitive Determination of Particulate, Gaseous Inorganic and Organic Iodine-129 and Iodine-127 in Ambient Air.

Atmospheric iodine cycling is of significance in climate change and environmental and health impacts. To better explore speciation transformation of atmospheric stable and radioactive iodine, an ultra-sensitive analytical method was established for determination of 129I and 127I in particulate, gaseous inorganic, and gaseous organic species, which was conducted with a self-designed cascade sampling apparatus, followed by their separation with a pyrolysis system and accelerator mass spectrometry and ICP-MS measurements. Combustion protocols for three sampling matrices and NaOH concentration for iodine trapping were optimized to achieve a safe analytical procedure with a high chemical yield of iodine. Based on the lowest concentrations of 129I and 127I, a suitable activated carbon product for adsorption of gaseous organic iodine was carefully selected. The detection limits of the three species were 0.30-2.21 ng m-3 for 127I and 0.05-0.22 × 105 atoms m-3 for 129I. This newly established method was successfully applied to analyze the levels and species of 129I and 127I in ambinet air from Xi'an, China, from May to August, 2020. Gaseous organic iodine was found to be the dominant species of 127I and 129I, accounting for about half of total iodine, and gaseous inorganic iodine and particulate iodine accounted for one-quarter each during the whole sampling period. Speciation variation of 129I and 127I indicates that speciation transformation apparently occurred at the turn of spring and summer, mainly between particulate and gaseous organic iodine. This study has implications on delicate tracing of the atmospheric behavior of iodine with long-lived anthropogenic 129I.

Recycling and persistence of iodine 127 and 129 in forested environments: A modelling approach

Differences in the source and behaviour of 129I compared to 127I isotopes have been described for a variety of surface environments, but little is known about the cycling rates of each isotope in terrestrial ecosystems. We developed a compartment model of the iodine cycle in a forest ecosystem, with a labile and non-labile pool to simplify the complex fate of iodine in the forest floor and soil. Simulations were performed using atmospheric 127I and 129I inputs for sites differing in climate, vegetation, and soil. In general, considering dry deposition in addition to wet deposition improved model simulations. Model results support the view that soil is the sink for atmospheric iodine deposited in forest ecosystems, while tree vegetation has little influence on long-term iodine budgets. Modelling also showed that iodine cycling reaches equilibrium after a period of about 5000 years, mainly due to a gradual incorporation of iodine into the bulk stabilised soil organic matter. At steady state, this pool of non-labile iodine in soil can retain about 20% of total deposition with a mean residence time of 900 years, while the labile iodine pool is renewed after 90 years. The proportions of modern anthropogenic 129I in each modelled pool reflect those of stable 127I at least several decades after input to the forest; this result explains why isotopic disequilibrium is common in field data analysis. Volatilisation plays a central role in regulating iodine storage in soil and, therefore, its residence time, while drainage is a minor export pathway, except at some calcareous sites. Dynamic modelling has been particularly helpful for gaining insight into the long-term response of iodine partitioning to continuous, single or even varying deposition. Our modelling study suggested that better estimates of dry deposition of atmospheric iodine, weathering of parent rock, and volatilisation of the deposited iodine from soil and vegetation will be required for reliable predictions of iodine cycling in specific forests, because these processes remain insufficiently explored.

Migration of iodine-129 and iodine-127 in soils

Abstract To draw the balance of anthropogenic 129I input into European soils, the concentrations of 129I and 127I in seven soils from Lower Saxony were analyzed down to a depth of 250 cm. In comparison with pre-nuclear soils and Ukrainian soils, we detected a significant anthropogenic input of 129I. Considering the different time periods for the input of 129I and 127I it was possible to assess the dynamics of sorption processes which dominate migration and accumulation. Anthropogenic 129I was successfully used as a tracer for a clarification of the migration processes of trace elements in soils.

Occurrence, evolution and degradation of heavy haze events in Beijing traced by iodine-127 and iodine-129 in aerosols

Heavy haze events have become a serious environment and health problem in China and many developing countries, especially in big cities, like Beijing. However, the factors and processes triggered the formation of secondary particles from the gaseous pollutants are still not clear, and the processes driving evolution and degradation of heavy haze events are not well understood. Iodine isotopes (127I and 129I) as tracers were analyzed in time series aerosol samples collected from Beijing. It was observed that the 127I concentrations in aerosols peaked during the heavy haze events. The conversion of gaseous iodine to particular iodine oxides through photochemical reactions provides primary nuclei in nucleation and formation of secondary air particles, which was strengthened as the external iodine input from the fossil fuel burning in the south/southeast industrial cities and consequentially induced heavy haze events. Anthropogenic 129I concentrations peaked during clean air conditions and showed high levels in spring and later autumn compared to that in summer. 129I originated from the direct air discharges and re-emissions from contaminated seawaters by the European nuclear fuel reprocessing plants was transported to Beijing by the interaction of Westerlies and East Asian winter monsoon. Three types of mechanisms were found in the formation and evolution of heavy haze events in Beijing by the variation of 127I and 129I, i.e., iodine oxides intermediated secondary air particles, dust storm and mixed mode by both secondary air particles and dust storm induced processes.

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.

Records of iodine isotopes (129I, 127I) in the Barkol peat bog from northwest China and their sources, transport and preservation

The research on geochemical behaviors of iodine is significant for deep understanding of the source and distribution of iodine on the earth. However, as one of the most important sources, the ocean emissions and relative transport pathways of iodine, as well as the preservation after deposition are still not well known, especially in the arid areas of central Asia. A peat sediment core collected nearby Barkol Lake from northwest China was analyzed for iodine isotopes (127I and 129I). The observed high 127I concentration in the top 2 cm indicated a significant accumulation of iodine in the surface oxic conditions due to the continuous sources of incompletely decomposed organic matter. Dissociation of iodine into pore waters occurred once the anoxic conditions established beneath the surface by a serial reduction reaction during the degradation of organic matter. The temporal variation of anthropogenic 129I in the peat sediment recorded its sources and transport pathways. Besides the global fallout 129I during late 1950s and early 1960s, the significantly increased air releases from the European nuclear fuel reprocessing plants during 1975–1997 and the increased marine discharges since 1990s contributed the major portion of 129I in the peat core. The major transport pathway of 129I from the Europe was through Westerlies following the re-emission of the marine discharged 129I to the atmosphere, indicating a clearly ocean emitted iodine in the concerned central Asia.

Circulation timescales of Atlantic Water in the Arctic Ocean determined from anthropogenic radionuclides

Abstract. The inflow of Atlantic Water to the Arctic Ocean is a crucial determinant for the future trajectory of this ocean basin with regard to warming, loss of sea ice, and ocean acidification. Yet many details of the fate and circulation of these waters within the Arctic remain unclear. Here, we use the two long-lived anthropogenic radionuclides 129I and 236U together with two age models to constrain the pathways and circulation times of Atlantic Water in the surface (10–35 m depth) and in the mid-depth Atlantic layer (250–800 m depth). We thereby benefit from the unique time-dependent tagging of Atlantic Water by these two isotopes. In the surface layer, a binary mixing model yields tracer ages of Atlantic Water between 9–16 years in the Amundsen Basin, 12–17 years in the Fram Strait (East Greenland Current), and up to 20 years in the Canada Basin, reflecting the pathways of Atlantic Water through the Arctic and their exiting through the Fram Strait. In the mid-depth Atlantic layer (250–800 m), the transit time distribution (TTD) model yields mean ages in the central Arctic ranging between 15 and 55 years, while the mode ages representing the most probable ages of the TTD range between 3 and 30 years. The estimated mean ages are overall in good agreement with previous studies using artificial radionuclides or ventilation tracers. Although we find the overall flow to be dominated by advection, the shift in the mode age towards a younger age compared to the mean age also reflects the presence of a substantial amount of lateral mixing. For applications interested in how fast signals are transported into the Arctic's interior, the mode age appears to be a suitable measure. The short mode ages obtained in this study suggest that changes in the properties of Atlantic Water will quickly spread through the Arctic Ocean and can lead to relatively rapid changes throughout the upper water column in future years.

Anthropogenic 129I in the South China Sea and coastal waters around Taiwan

In this article, we present a study of seawater 129I/127I time-series data from several coastal sites in Taiwan, including Yehliu Geopark (north–northeast coast), Kaohsiung (southwest coast), and Zhuwei Fishing Village (northwest coast). The objective of this study was to document how 129I/127I responds to known seasonal variations in the surface ocean currents that carry 129I to each of these sites. The responses were shown to be quite distinct. The Zhuwei site, across Mainland China, had elevated spring and summer 129I/127I values, with abrupt peaks that reflected transient cross-strait currents that carry seawater with elevated 129I to the northwest coast of Taiwan. The Yehliu site, which receives all of its seawater from the Kuroshio Current, had relatively low and uniform 129I/127I values year-round. The Kaohsiung site showed a summertime minimum that likely stems from upwelling upstream induced by oceanic eddies associated with the Kuroshio intrusion. To our knowledge, these are the first continuous coastal 129I/127I time-series data published for Asian waters and the first to show large, abrupt, and regional 129I/127I changes in the surface seawater. We also documented 129I/127I values from multiple surface ocean sites in the South China Sea (SCS), including a vertical profile from the South East Asia Time-Series Station that extends to a depth of 3,700 m. The 129I from both coastal Taiwan and surface waters of the SCS is >98% anthropogenic, primarily released to the environment as a byproduct of nuclear fuel reprocessing.

Circulation of Circumpolar Deep Water and marine environment traced by 127I and 129I speciation in the Amundsen Sea Polynya, Antarctica

The long-lived anthropogenic 129I released from human nuclear activities has been widely employed as an effective oceanographic tracer to investigate circulation of water masses in marine environment. Depth profiles of seawater collected from the Amundsen Sea Polynya, Antarctica were analyzed for total 129I and 127I, as well as their species of iodide and iodate. The measured 129I concentrations ((1.15–3.43) × 106 atoms/L) and 129I/127I atomic ratios ((0.53–1.19) × 10−11) indicate that anthropogenic 129I has not only reached the Antarctic surface marine environment but also the deep water due to a strong vertical mixing of water masses. The Circumpolar Deep Water (CDW) flowed southward along continental shelf towards the ice shelf zone (74.25°S) at a depth of 1025 m and then migrated upward and northward to the polynya and finally to the sea ice zone (71.95°S). The maximum upwelling depth of the CDW was around 200 m in the polynya. The source of 129I− in the polynya is predominantly the intrusion of source waters rather than the in-situ reduction of iodate by phytoplankton, implying a considerably slow reduction process of iodate to iodide in this region.

An investigation of 129I from regional nuclear fuel reprocessing in the terrestrial sediments of Lake Ontario

129I (T1/2 = 15.7 Ma) concentrations were measured in sediments from Lake Ontario, whose drainage basin contains a former nuclear fuel reprocessing facility. Three archived sediment cores had 129I concentrations from approximately 1 × 105 atoms/g in deeper sections to 1 × 109 atoms/g at the surface, elevated above the nuclear weapons testing signal for North America. 129I concentrations and 129I/127I ratios increase upwards and indicate a significant anthropogenic influence, with the vast majority of the 129I in each core being found near the surface. There is also some penetration into deeper sediment layers, with pre-nuclear 129I/127I ratios only reached at depths of 10–13 cm. The data show that Lake Ontario sediments are a repository for anthropogenic 129I from regional nuclear fuel reprocessing. The results point to the mobilization of iodine from anoxic, deeper sediment layers, shedding light on the geochemical behavior of iodine isotopes in Lake Ontario’s sediments.