Water Circulation and Marine Environment in the Antarctic Traced by Speciation of 129I and 127I

Abstract

Emissions of anthropogenic 129I from human nuclear activities are now detected in the surface water of the Antarctic seas. Surface seawater samples from the Drake Passage, Bellingshausen, Amundsen, and Ross Seas were analyzed for total 129I and 127I, as well as for iodide and iodate of these two isotopes. The variability of 127I and 129I concentrations and their species (127I−/127IO3 −, 129I−/129IO3 −) suggest limited environmental impact where ((1.15–3.15) × 106 atoms/L for 129I concentration and (0.61–1.98) × 10−11 for 129I/127I atomic ratios are the lowest ones compared to the other oceans. The iodine distribution patterns provide useful information on surface water transport and mixing that are vital for better understanding of the Southern Oceans effects on the global climate change. The results indicate multiple spatial interactions between the Antarctic Circumpolar Current (ACC) and Antarctic Peninsula Coastal Current (APCC). These interactions happen in restricted circulation pathways that may partly relate to glacial melting and icebergs transport. Biological activity during the warm season should be one of the key factors controlling the reduction of iodate in the coastal water in the Antarctic.

Spatial and vertical distribution of 129I and 127I in the East China Sea: Inventory, source and transportation

“…The spatial distribution pattern of 129 I is the opposite of that of 127 I, i.e., 129 I is higher in the Changjiang Estuary but relatively lower in the offshore seawater. The measured 129 I concentrations in the surface seawater in this study are comparable to the reported values in surface water of the North Pacific (20°N-45°N) ((0.59-3.7) × 10 7 atoms L -1 ) (Guilderson et al, 2014), Japan Sea ((0.28-5.8) × 10 7 atoms L -1 ) (Cooper et al, 2001), and southern Indian Ocean ((0.60-0.80) × 10 7 atoms L -1 ) (Povinec et al, 2011), but higher than that in Antarctic region ((0.11-0.31) × 10 7 atoms L -1 ) (Xing et al, 2017), lower than that in the Bering Sea ((1.8-131) × 10 7 atoms L -1 ) (Cooper et al, 2001) and North Atlantic (31°N-50°N) ((4.0-127) × 10 7 atoms L -1 ) , and much lower than that in the Baltic Sea ((0.25-17) × 10 10 atoms L -1 ) (Yi et al, 2011), North Sea ((0.26-38) × 10 10 atoms L -1 ) (Hou et al, 2007), Celtic Sea ((0.03-1.2) × 10 10 atoms L -1 ) (He et al, 2014) and Irish Sea ((6.2-47) × 10 10 atoms L -1 ) (Schnabel et al, 2007), where there they were heavily contaminated by the discharge from the reprocessing plants at La Hague (France) and Sellafield (UK).…”

“…Iodine-127 ( 127 I) is a stable isotope, and 129 I/ 127 I atomic ratios (described as ratios in the following text) largely vary depending on the source of iodine in the marine environment. These ratios range from 3×10 -12 to 2×10 -6 , which are higher than the prenuclear level (1.5×10 -12 ) (Fehn et al, 2000;Xing et al, 2017). So, 129 I/ 127 I ratio is very useful for identifying the source of 129 I and for water mass movements in marine environments.…”

“…Considering its long half-life and relatively low beta-energy (with a maximum beta-emitted energy of 154 keV), 129 I is not very radiologically harmful in common situation. Instead, 129 I is widely utilized as a tracer for the biogeochemical cycle of iodine, the movement and exchange of water masses, and the interactions between atmosphere and seawater in marine environments (Hou et al, 2007;Zhang and Hou, 2013;Xing et al, 2017). Due to its high solubility (Kd: 5-30 L kg -1 , Takata et al, 2013) and long residence time in the ocean (~300 kyrs) compared to the turnover time of ocean water (~1000 kyrs, Broecker and Peng, 1982), it can be utilized to trace the cycling of dissoluble organic carbon and phytoplankton blooming associated with reductive conditions (Schwehr et al, 2005;Hou and Hou, 2012;Liu D. et al, 2016).…”

Microbiome interactions and their ecological implications at the Salton Sea

“…Multiple sample types (e.g., dust, water, playa) should be collected, at a variety of time points, from a replicated set of diverse locations within and around the Sea. As sample collection procedures will differ between media types (soil cores, dust collection, water samples), technological advances, such as the use of drones, water skimmers or seawater samplers (Xing et al 2017), could be advantageous. Other valuable approaches may use semi-permanent passive samplers (Aciego et al 2017;Frie et al 2019), portable sampling platforms (Docherty et al 2018) or active samplers, which collect all airborne cells and spores using filters from a known air volume (Frie et al 2017).…”

Determination of 129I in environmental solid samples using pyrolysis separation and accelerator mass spectrometry measurement

“…We have proposed a separation method of carrier free 129 I using AgI-AgCl precipitation [17], which has been successfully used for determination of 129 I in seawater and precipitation from the Antarctic [28,29]. In the analysis of environmental solid samples, such as rock sample, small amount of chloride (0.5 mg) can be added to the trap solution, the formed AgI-AgCl co-precipitate is then separated by centrifuge after addition of sufficient amount of AgNO3.…”