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

Anthropogenic radioisotopes produced by fission of uranium or plutonium are characteristic markers of the Anthropocene (Zalasiewicz et al., 2015). Among these, ¹²⁹I occupies a special niche because unlike other fission products, it continues to be released to the environment as a by-product of nuclear fuel reprocessing, and the amount of ¹²⁹I in the environment continues to grow. These releases are permitted because ¹²⁹I is a relatively benign isotope with a very long half-life (15.7 × 10⁶ year), low specific activity, and relatively low-energy decay products (Edwards, 1962). The first large-scale releases of anthropogenic ¹²⁹I into the environment occurred in the late 1950s and early 1960s from aboveground nuclear weapons testing. These produced an estimated 90 ± 45 kg of ¹²⁹I compared to a prenuclear marine inventory of about 130 kg (Snyder et al., 2010) produced naturally from fission of ²³⁸U and by interactions between cosmic rays and Xe in the atmosphere (Edwards, 1962; Fabryka-Martin et al., 1985). Aboveground nuclear weapons testing produced peak oceanic ¹²⁹I/¹²⁷I concentrations preserved in banded corals (Biddulph et al., 2006; Bautista et al., 2016; Chang et al., 2016; Sakaguchi et al., 2018) and in marine sediments (Fan et al., 2016; Zhao et al., 2019). In the ensuing years, after the era of atmospheric weapons testing, these marine archives also document a second, and much larger, anthropogenic source of ¹²⁹I.

This second source comes primarily from nuclear fuel reprocessing plants that recover economic isotopes from spent nuclear fuel rods. On a global scale, the two most significant ¹²⁹I sources to date are the Sellafield (England) and La Hague (France) commercial nuclear fuel reprocessing plants (Raisbeck and Yiou, 1999; Reithmeier et al., 2006; Hou et al., 2009; Hu et al., 2010b). The amount of ¹²⁹I in the world’s oceans was recently estimated to have reached 7,310 kg (Chen et al., 2016). This estimate implies that as much as 98% of the ¹²⁹I in the oceans is anthropogenic and that approximately only 1% of that anthropogenic ¹²⁹I came from atmospheric nuclear weapons testing. Hence, the amount of ¹²⁹I in the oceans has increased by about a factor of 60 from a prenuclear value of 130 kg, to 7,310 kg. According to the International Atomic Energy Agency (IAEA), from the onset of nuclear power production in 1954 to 2013, approximately 370,000 metric tons of heavy metal (t HM) in spent fuel has been consumed, and about one-third of that (120,300 t HM) has been reprocessed (IAEA, 2018). Most of the remaining spent fuel is stored at the 236 nuclear power stations where it was produced, and the ¹²⁹I it contains has not yet been released to the environment (Hou et al., 2009; Hu et al., 2010b).

The increase in the amount of ¹²⁹I in the oceans over the past 70 years makes clear that the rate of iodine removal by natural sinks is slower than the rate of its release by reprocessing plants. Anthropogenic marine ¹²⁹I measurements from around the world also show that neither the shallow ocean nor the deep ocean is in equilibrium with ¹²⁹I (Snyder et al., 2010). As a small subset of this global picture, we examined how seawater ¹²⁹I values change with time in the vicinity of Taiwan in 2018 and 2019, with an emphasis on seasonal variations seen in time-series data collected regularly from several sites around the island.

Iodine is a very mobile element in nature that forms few minerals; its geochemistry is dominated by oceanic and atmospheric transport and storage (Fuge and Johnson, 1986). Iodine in seawater occurs as dissolved iodide, iodate, organic iodine, and particulate iodine (Wong, 1991; Santschi and Schwer, 2004). The concentration of dissolved iodine in seawater is about 60 µg L⁻¹, and although iodine is a very mobile element, ¹²⁹I can be used as a semiconservative −tracer in seawater to determine current pathways, transit times, and water mass mixing. A number of tracer studies of this type have been conducted in the North Atlantic Ocean and the Arctic Ocean, downstream from the release sites at Sellafield and La Hague (Raisbeck and Yiou, 1999; Alfimov et al., 2004; Smith et al., 2005), and in recent years, such studies have been refined by combining ¹²⁹I with other anthropogenic isotopes (i.e., ¹³⁷Cs, ⁹⁹Tc, and ²³⁶U) to better discriminate between point sources and to determine more accurate transit times (Smith et al., 1998, 2011; Yiou et al., 2002; Christl et al., 2015; Casacuberta et al., 2018).

Tracer studies rely on time-series data to determine pathways, rates, and deposition of anthropogenic isotopes. Marine ¹²⁹I time series can be derived from seawater (Chang et al., 2019), seaweed (Raisbeck and Yiou, 1999; Yiou et al., 2002), corals (Biddulph et al., 2006; Bautista et al., 2016; Chang et al., 2016; Sakaguchi et al., 2018), sediments (Fan et al., 2016; Zhao et al., 2019), or models (Alfimov et al., 2006; Smith et al., 2011). Seaweed and corals allow for time series with sub-annual to annual resolution. The time resolution of seawater samples is limited only by the rate at which samples are collected, which can be tailored to meet specific goals. Here, we chose bimonthly (every 2 weeks) resolution in order to document seasonal ¹²⁹I variations. This seasonal variability complements ¹²⁹I/¹²⁷I time-series studies from corals, with annual resolution.

Open ocean sites in the South China Sea (SCS) were sampled in 2018, and coastal time-series sample collection began in 2018 or 2019 depending on the site. Three sites were investigated: (1) Yehliu Geopark (25.205N, 121.692E), (2) Kaohsiung (22.624N, 120.263E), and (3) Zhuwei Fishing Village (25.121N, 121.252E; Figure 1). None of these sites is located near a major river. The Zhuwei Fishing Village and Yehliu Geopark sites are only 45 km apart, but their seawater sources are very different. The Zhuwei site faces the northern end of the Taiwan Strait where it connects to the East China Sea (ECS), while the Yehliu site faces the Pacific Ocean. The Kaohsiung site, on the campus of National Sun Yat-Sen University (Figure S1), also faces the Taiwan Strait but on the southwest coast of Taiwan (Figure 1). Open ocean sites were sampled during a cruise of the R/V Legend (LGD-T11) from July 4 to 12, 2018. These included a number of surface sites (5-m depth) and a vertical profile from the South East Asia Time-series Study (SEATS) site (Figure 1).

Figure 2 shows the surface ocean currents that affect the coastal sites selected for this study. The most dominant current affecting Taiwan is the Kuroshio Current, a western boundary current of the North Pacific Ocean, which flows from south to north along the east coast of the Philippines and then along the east coast of Taiwan. The Kuroshio Current has a mean geostrophic volume transport of approximately 15 Sv (1 Sverdrup = 10⁶ m³ s⁻¹) as it passes the northern tip of Luzon Island, with maximum transport in spring and minimum transport in fall (Qiu, 2019). When the Kuroshio Current passes this point, a portion of its waters enters the SCS through the Luzon Strait (Chu and Li, 2000; Hu et al., 2000). This portion is known as the Kuroshio intrusion. The Kuroshio intrusion can follow several pathways after it diverts westward from the main stream of the Kuroshio Current: (1) along the shelf break and to the southwest, (2) northward through the Penghu Channel (the Kuroshio Loop Current extension), or (3) toward the northeast, where it rejoins the main Kuroshio stream (Hu et al., 2000, 2010a; Qiu et al., 2011). Nan et al. (2011) defined a Kuroshio SCS index (KSI) based on geostrophic vorticity to quantify analogous intrusion pathways as a leaking path, looping path, or leaping path. Although the Kuroshio intrusion can follow any of these paths at any time, the leaking and looping paths are most probable in autumn, winter, and spring, and the leaping path is most probable in summer (Nan et al., 2015). This seasonality is associated with the Southeast Asian monsoon. Regardless of the path, the Kuroshio intrusion contributes to the seasonal flow of water through the Taiwan Strait and is responsible for its northward flow year-round. Estimates of the westward volume transport of Kuroshio water through the Luzon Strait range from approximately 3 Sv to >10 Sv (Nan et al., 2015), while the northward volume transport through the Taiwan Strait is approximately 2.3 Sv in summer and approximately 0.8 Sv in winter (Hu et al., 2010a).

The method we describe below extracts dissolved iodine from seawater; in this study, “total iodine” and “total ¹²⁹I/¹²⁷I” are operationally defined as the iodine extracted using our technique. As noted above, dissolved iodine in seawater occurs in three forms: inorganic iodide (I⁻), inorganic iodate (⁠$IO3−$⁠), and organic iodine. Our method extracts iodide, iodate, and organic species where iodine is loosely bound, such as methyl iodide. Many sensitive methods have been devised to extract and quantify individual dissolved inorganic ¹²⁹I species (Hou et al., 1997) and dissolved organic species (Schwehr and Santschi, 2003; Zhang et al., 2010). These provide valuable tools to understand ¹²⁹I pathways and their kinetics. However, in this study, we are concerned only with the bulk anthropogenic ¹²⁹I carried in the seawater. Exchange between various species within a parcel of water will not change the total amount of anthropogenic iodine within it.

We also do not consider stable (¹²⁷I) iodine concentrations because stable iodine is very uniform in the surface ocean (Fuge and Johnson, 1986; Wong, 1991; Chance et al., 2014). In one large study, for example, surface waters from a vast area of the Pacific (>20°N, 137–163°E) were shown to vary by less than 3% (Tsunogai and Henmi, 1971). This level of variation falls within the errors of our ¹²⁹I/¹²⁷I measurements and cannot explain variations larger than a few percentage.

Surface water from open ocean sites was obtained during a cruise of the R/V Legend (LGD-T11) from July 4 to 12, 2018 (Figure 1). Samples for an ¹²⁹I/¹²⁷I depth profile were collected at the SEATS site (18.120°N, 116.052°E) on July 8, 2018. The depth profile samples were collected with Teflon-lined 12-L Go-Flo bottles mounted on a conductivity-temperature-depth/Rosette frame, which also measured fluorescence (Chlorophyll a) with depth. Upon recovery of the Go-Flo bottles, each open ocean sample was filtered through a 0.22-µm Polycap filter cartridge into a 1-L low-density polyethylene bottle. Surface water samples at 5-m depth were collected from a Teflon pipe in the wet lab on deck using a diaphragm pump. All the water samples were kept under 4°C before shipment to the laboratory. Two liters of seawater were collected from each coastal site (Figure S1) at 2-week intervals using 1-L high-density polyethylene bottles.

Coastal seawater samples were filtered in the laboratory with 0.22-µm nylon membrane filters. Iodine was extracted from the filtered seawater in 1-L batches using the following steps (Chang et al., 2019): (1) the sample was placed in a 1-L separatory funnel, (2) it was acidified to pH < 2 using phosphoric acid (H₃PO₄), (3) 2.5 mL of 0.48 M sodium bisulfite (NaHSO₃) was added and allowed to react overnight, (4) 5.4 mL of 1.0 M sodium nitrite (NaNO₂) was added to the sample, and (5) I₂ was extracted using chloroform in a separatory funnel as an immiscible solvent. Steps 4 and 5 were repeated 3 times to assure complete removal of the iodine produced using 0.4 mL of NaNO₂ in each successive extraction. The chloroform was decanted into 20-mL vials with about 10 mg of silver powder, which reacted with the I₂ to form AgI. The chloroform was allowed to evaporate, and the AgI was rinsed repeatedly and dried. No carrier was added to the sample. The reactions that occur during each step of the extraction are given in the Supplemental Material (Text S1) along with a photograph of the chloroform extraction step (Figure S2).

The accelerator mass spectrometric measurements were performed at the Micro Analysis Laboratory, Tandem Accelerator (MALT) facility, University Museum, University of Tokyo, using established measurement protocols (Matsuzaki et al., 2015). AgI samples were mixed with Nb powder and pressed into aluminum target holders for accelerator mass spectrometric analyses. The measurements were conducted at a terminal voltage of 3.48 MV, and particles in the 5+ charge state were selected. ¹²⁹I/¹²⁷I values were calculated relative to the S-Purdue 2 standard with a nominal ¹²⁹I/¹²⁷I ratio of 6.54 × 10⁻¹¹. The machine blank for ¹²⁹I/¹²⁷I at the MALT facility is below 1.5 × 10⁻¹⁴. Uncertainties were calculated based on counting statistics (Burr et al., 2007) using the number of counts observed in the samples and standards. Machine instabilities were also taken into account.

Chlorophyll a was measured using a fluorescence meter mounted as an auxiliary detector on an SBE 9 plus conductivity-temperature-depth profiling recorder (Seabird Scientific) with a detection resolution of 1 datum/s. The fluorescence technique followed standard protocols for the method (Roesler et al., 2017). The instrument was calibrated at the Taiwan Ocean Research Institute immediately prior to the cruise. Chlorophyll a values and their uncertainties are given in Table S1 based on about 500 measurements at each depth interval.

We report three types of ¹²⁹I/¹²⁷I results: (1) open ocean surface water (5-m depth; Table 1), (2) a vertical profile from the SEATS site (Table 2), and (3) surface seawater time-series results from the coastal sites (Table 3). All of the measured values are given in the tables along with site details, collection dates, and number of ¹²⁹I particles detected. The Kaohsiung time-series results were reported previously in the Proceedings of the 8th East Asia AMS Symposium (Burr et al., 2020) and are included here to facilitate comparison.

The SCS is the largest marginal sea in Southeast Asia with water depths of more than 5,000 m and a very broad continental shelf along its western border. As the basin is largely restricted and the climate is monsoonal, the surface circulation in the SCS is driven by the monsoon, with a seasonal reversal of surface current directions (Wyrtki, 1961). The mean circulation of the upper layer (0–200 m) of the SCS is cyclonic in winter and anticyclonic in summer (Hu et al., 2000). Circulation is also dependent on the Kuroshio intrusion as discussed above. Most of the seawater that replenishes the SCS ultimately comes from the Kuroshio Current, with a net westward flow through the Luzon Strait (Hu et al., 2010a; Nan et al., 2015). In addition to seasonal variations, both the Kuroshio intrusion and Kuroshio Current exhibit significant interannual variability in terms of pathways and volume transport, and the Kuroshio intrusion causes the formation of mesoscale eddies that promote vertical mixing, especially in winter (Caruso et al., 2006; Hu et al., 2010a; Nan et al., 2015; Qiu, 2019). As shown below, ¹²⁹I/¹²⁷I is very sensitive to vertical mixing.

The locations of the open ocean sites sampled for this study are shown in Figure 1. Taiwan Strait sites (TS a and TS b) receive water from the Kuroshio Loop Current extension in the Penghu Channel (Figure 2). The Dongsha Island site (DS) and Northern South China Sea site (NSCS) are situated in the path of the SCS Warm Current (Figure 2). The Luzon Strait sites (LZ a and LZ b) are located in the Luzon Strait, where water from the Kuroshio intrusion enters the SCS. Despite their hydrographic differences, the ¹²⁹I/¹²⁷I values at these surface water sites were statistically indistinguishable as shown in Figure S3. That is, all individual measured values overlap with the weighted mean for the group: ¹²⁹I/¹²⁷I = 49.1 ± 2.4 × 10⁻¹² (2σ external variance) during the sample collection period from July 4 to 12, 2018. This average gives us a reference value for the northern SCS, upstream from the Taiwan Strait, to compare with our coastal sites further north, at Kaohsiung and Zhuwei Fishing Village. Our SCS surface ocean results are typical of the open ocean in the region and overlap with southeastern ECS values in the range of 20–60 × 10⁻¹² reported elsewhere (Liu et al., 2016; Wang et al., 2019). They also overlap with surface water values measured at the SEATS site, discussed next.

The SEATS site is located in a deep basin, south of the open ocean sites (Figure 1). Results were obtained from 14 samples at progressive depths from 10 to 3,700 m (approximately 100 m above the seafloor) on July 8, 2018. ¹²⁹I/¹²⁷I values ranged from deep water values of approximately 1.2 × 10⁻¹² to surface water values of approximately 50.8 × 10⁻¹² (Table 2 and Figure 3). The deep water values are typical prenuclear marine values and agree with those reported by Yi et al. (2018) from a nearby site (Figure 3) and from several deep water sites off the northeast coast of Japan (Suzuki et al., 2010, 2018). Our SEATS profile shows that surface water ¹²⁹I/¹²⁷I values in 2019 were enriched by a factor of about 50 above SCS deep waters. Hence, ¹²⁹I is a very sensitive upwelling indicator. The ¹²⁹I/¹²⁷I depth profile we observed is typical of marine depth profiles, with most of the ¹²⁹I contained in the surface layer of the ocean. The profile observed by Yi et al. (2018), measured from a nearby site 4 years prior to our sampling, is very different with respect to depth in the water column. However, the overall shape of the two profiles is similar, and they have overlapping surface and deep water values. The interannual variability of mesoscale eddies associated with the Kuroshio intrusion north of the site could contribute to the vertical mixing observed in 2014. As these are the only two ¹²⁹I/¹²⁷I depth profiles currently available, conjecturing further would be premature.

An interesting feature in our record is an increase in ¹²⁹I/¹²⁷I (from 1.2 to approximately 6 × 10⁻¹²) near the seafloor at 3,500 m depth. This increase suggests remobilization of particulate iodine associated with sinking organic matter or particulate iodine. Based on the work of Brewer et al. (1980), Wong (1991) estimated that about 4% of the particulate iodine in surface ocean waters can settle to the deep ocean, and as much as 95% of that iodine can be dissolved at the water–sediment interface, providing a potential pathway to explain our observed deep water ¹²⁹I signal (Figure 3). An inflection point is also observed in our ¹²⁹I/¹²⁷I profile between 65 and 200 m depth (Figure 3). Iodine is a biophilic element known to be scavenged by marine organisms, especially seaweed (Fuge and Johnson, 1986; Hou et al., 1997; Santschi and Schwer, 2004). Our measured peak Chlorophyll a concentrations (approximately 77 m depth) coincide with the ¹²⁹I/¹²⁷I inflection seen in our profile (Figure 3).

Measured ¹²⁹I/¹²⁷I time series from Yehliu Geopark, Kaohsiung (Burr et al., 2020), and Zhuwei Fishing Village are given in Table 3. The 1σ precision of the measurements was <5% and improved as the study progressed with refinements to the sample processing protocol that included larger sample volumes (up to 2 L) and longer reaction times (overnight) after the addition of sulfite. With reference to the surface ocean currents summarized in Figure 2, we can follow the marine pathways of iodine in the vicinity of Taiwan. The most straightforward of these pathways involves the Yehliu site, which is dominated by the Kuroshio Current as it passes the northern tip of Taiwan. Over the entire observation period (March–November 2019), the Yehliu data are very consistent, with no seasonal trend. At two standard deviations, the average value varies by less than 4%, with a weighted average of ¹²⁹I/¹²⁷I = 48.61 ± 1.90 × 10⁻¹² (2σ external variance). These low values reflect the large volume of water carried by the Kuroshio Current, which passes no significant anthropogenic ¹²⁹I source in its path and is apt to inherit low-¹²⁹I upwelled waters from its parent current, the North Equatorial Current, and from mesoscale eddies (Qiu, 2019).

Kaohsiung has a direct connection with the Kuroshio Current by way of the Kuroshio Loop extension that flows northward through the Penghu Channel along the southwestern coast of Taiwan (Figure 2). This region is the only part of the west coast of Taiwan where surface currents flow northward year-round, every year (Qiu et al., 2011). Upstream from Kaohsiung is an area where seasonal cold core eddies form, driven by the Kuroshio intrusion (Li et al., 1998). Cold core eddies induce vertical mixing and can dilute surface water ¹²⁹I. This effect is what we observed during the summer of 2019 at Kaohsiung, where surface water ¹²⁹I/¹²⁷I dropped from 48.07 ± 4.10 × 10⁻¹² on June 9 to 38.5 ± 4.2 × 10⁻¹² (2σ) on July 22 during the summer monsoon. This minimum is well below our SCS surface water average value, 49.1 ± 2.4 × 10⁻¹², and is the lowest value among seven consecutive measurements that define a smooth minimum over a 3-month period (Figure 4). On a longer time scale, our Kaohsiung time-series data are consistent with ¹²⁹I/¹²⁷I measurements from the same site, which ranged from approximately 36 to 53 × 10⁻¹² between 2011 and 2015 (Chang et al., 2019).

At Zhuwei Fishing Village, we recorded the highest ¹²⁹I/¹²⁷I values of any site, as much as 2.4 times the average for Yehliu, which is only 45 km away (Figure 5). Clearly, this high level of ¹²⁹I did not come from the direction of Yehliu because of the low values there, as well as the southern ECS in general (Liu et al., 2016). However, Liu et al. (2016) identified high ¹²⁹I/¹²⁷I values (up to approximately 200 × 10⁻¹²) in the Yangtze River Estuary and in coastal waters that extend to the south. The China coastal current flows toward the south, off the coast of Mainland China, and carries water into the Taiwan Strait. During the winter and spring, transient cross-strait surface flow can develop (Liao et al., 2018), shown as the dashed current trajectory in Figure 2. Hence, we have a known source and known pathway that can explain the two abrupt ¹²⁹I/¹²⁷I peaks at Zhuwei that we observed, and the relatively higher spring and summer values as mixtures of water from the China Coastal Current and surface seawater from the south. Although Zhuwei is located at the narrowest stretch of the Taiwan Strait (130 km), surface water need not flow directly across to arrive there. Water can cross at any point to the north or south, because although coastal waters along the northwest coast of Taiwan generally flow northward, they have also been observed to flow to the south at times (Qiu et al., 2011). Our ¹²⁹I results demonstrate that ¹²⁹I can serve as a useful indicator of this cross-strait flow, which was strongest in the spring and summer of 2019 at Zhuwei Fishing Village.

In this study, we have documented surface seawater ¹²⁹I/¹²⁷I from a large area in the SCS and found uniform values that reflect well-mixed waters. We documented a vertical ¹²⁹I/¹²⁷I profile to 3,700 m depth from the SCS SEATS site that shows prenuclear values in deep waters, a typical diffusive curve, and an ¹²⁹I/¹²⁷I enrichment of approximately 50 times in surface waters compared to deep waters. We followed the path of anthropogenic ¹²⁹I in ocean currents from the SCS to the east and west coasts of Taiwan. At Yehliu, all of the water comes from the Kuroshio Current and with no distinct seasonal effects. At Kaohsiung, we observed a summertime ¹²⁹I minimum likely associated with seasonal cold core eddies induced by the Kuroshio intrusion. At Zhuwei Fishing Village, we observed high spring and summer ¹²⁹I/¹²⁷I values with sporadic short-lived ¹²⁹I/¹²⁷I peaks that record transient periods of cross-strait flow with water likely coming from the China Coastal Current. To our knowledge, these data are the first continuous coastal ¹²⁹I/¹²⁷I time series published for Asian waters and the first to show abrupt changes in surface water ¹²⁹I/¹²⁷I in the coastal waters of Taiwan. In addition to revealing such local changes, studies of this type, and of anthropogenic isotopes in general, are useful for quantifying and understanding human impacts that define the Anthropocene.

A complete list of ¹²⁹I/¹²⁷I results cited in this study is included in the main body of the manuscript (Tables 1–3). Chlorophyll a data measured at the SEATS site are given in Table S1 of the Supplemental Material.

The supplemental files for this article can be found as follows:

Figure S1. Coastal sampling sites. Photographs of the three coastal sites studied in this article: (a) National Sun Yat-Sen University, Kaohsiung, (b) Yehliu Geopark, and (c) Zhuwei Fishing Village.

Figure S2. Extraction of iodine from seawater. Immiscible chloroform at the base of a separatory funnel with artificial seawater above. The purple color is from dissolved iodine from 20-µL methyl iodide dissolved in 1 L of artificial seawater.

Figure S3. Plot of ¹²⁹I/¹²⁷I values from open ocean sites in the South China Sea. The dashed line is the weighted average of these values, and the shaded error represents the 2σ uncertainty of the weighted average (49.1 ± 2.4 × 10⁻¹²). All samples overlap with the average within errors.

Table S1. Chlorophyll a results.

Text S1. Docx.

Sincere thanks to Chin-Wen Yang, at National Sun Yat-Sen University, who assisted with sample collection at Kaohsiung. We also thank the anonymous reviewers of our article who offered constructive criticisms that led to significant improvements in the final version. Many thanks to Professor Lin Li-Hung (NTU) and his many students for their assistance in the laboratory and technical advice. We are very grateful to the technical team and crew of the R/V Legend for their skillful support during the LGD-T11 cruise. We would also like to recognize the bus drivers of the number 1068 and 953 buses who provided reliable transportation and support.

We are grateful to the Taiwan Ministry of Science and Technology (MOST 107-2116-M-002-001-MY3) for funding, and funds cofinanced by the European Union and the State of Hungary in support of AJTJ, through the European Regional Development Fund project (GINOP-2.3.2-15-2016-00009 “ICER”).

The authors have no competing interests to declare.

Substantial contributions to conception and design: GB, HM, BSW, CCC, CHL.

Acquisition of data: GB, HM, BSW, HT, TY, SLW.

Analysis and interpretation of data: GB, HK, TLY.

Drafting the article or revising it critically for important intellectual content: GB, HM, BSW, AJTJ.

Final approval of the version to be published: GB, AJTJ.

How to cite this article: Burr, George S, Matsuzaki, H, Wang, B-S, Kusuno, H, Tokuyama, H, Yamagata, T, Yu, T-L, Wang, S-L, Chang, C-C, Jull, AJT, Lo, C-H. 2020. Anthropogenic ¹²⁹I in the South China Sea and coastal waters around Taiwan. Elem Sci Anth 8: 1..

Domain Editor-in-Chief: Jody W. Deming, School of Oceanography, University of Washington, Seattle, WA, USA

Associate Editor: Yusuke Yokoyama, Atmosphere and Ocean Research Institute, The University of Tokyo, Tokyo, Japan

Knowledge Domain: Ocean Science

Part of an Elementa Special Feature: Pan-Pacific Anthropocene