Progress on I-129 analysis and its application in environmental and geological researches

Iodine-129 is a naturally generated isotope, but anthropogenic releases are the dominated source of I-129 in the present environment. Among many measurement techniques, neutron activation analysis (NM) and accelerator mass spectrometry (AMS) are only methods used for measurement of I-129 in environmental level. Based on its source terms, chemical properties and environmental behaviors, I-129 can be applied for geological dating in a range of 2-80 Ma, investigation of formation and migration of hydrocarbon, circulation of ocean water, atmospheric process of iodine, as well as reconstruction of dispersion and migration of short-lived radioisotopes of iodine released from nuclear accidents. This article aims to summarize and critically compare the analytical techniques used for I-129 measurement and chemical methods for separation of iodine from various sample matrices, purification from the interferences, as well as preparation of suitable target for AMS measurement. The major applications in environmental and geological researches are reviewed, which mainly focus on the new progress and potential development in the future. The application of I-129 in the investigation of radioactive contamination from the Fukushima accident is discussed.</p

Analysis of low-level I-129 in brine using accelerator mass spectrometry

An improved solvent extraction procedure for iodine separation from brine samples has been applied at Xi&#39;an Accelerator Mass Spectrometry (AMS) center. Oil in the brine sample has to be removed to avoid appearance of the third phase during solvent extraction and to improve the chemical yield of iodine. The small amount of oil remained in the water phase was first removed by phase separation through settling down sufficiently based on their immiscibility, and then by filtration through a cellulose filter, on which oil was absorbed and removed. After oil removed, extraction recovery of iodine could achieve more than 90 %. The sodium bisulfite as an effective reductant should be added before acidification to avoid loss of iodine by formation of I-2 in sample via reaction of iodate and iodide at pH 1-2, and then pH was adjusted to 1-2 to reduce the iodate to iodide followed by oxidation of iodide to I-2 and solvent extraction to separate all inorganic iodine. As a pre-nuclear era sample, I-129/I-127 ratio in brine is normally more than two orders of magnitude lower than that in present surface environmental samples, so prevention of cross-contamination and memory effect in apparatus during processing procedure are very critical for obtaining reliable results, and monitoring the procedure blank is very important for analytical quality of I-129. The I-129/I-127 isotopic ratio in the brine samples and procedure blank of iodine reagents were measured to be (1.9-2.7) x 10(-13) and 2.08 x 10(-13), respectively, 3-4 orders of magnitudes lower than that in environmental samples in Xi&#39;an, and the result of procedure blank is in the same level as the previous experiments in past 3 years, indicating contamination is not observed in our method.</p

Variation of the winter monsoon in South China Sea over the past 183 years: Evidence from oxygen isotopes in coral

Oxygen isotope (&delta;18O) data in winter months in living coral Porites lutea collected from the Xisha Islands, South China Sea is significantly correlated to the measured winter monsoon velocity (WMV) with a correlation coefficient of 0.63. Based on 40-year (1961&ndash;2000) instrumental data, a transfer function between the WMV and the winter &delta;18O is established: WMV = 2.819 &delta;18O + 19.615 (N = 40, p &lt; 0.0001). Based on the calculated WMV from &delta;18O over the past 183 years, the sequence of winter monsoon velocity (WMV) from year 1818 to 2000 in the South China Sea is re-constructed. The sequence can be divided into three stages: the first stage shows a decreasing trend of 0.009 m/s&middot;yr from 1818 to 1954, the second stage indicates an increasing trend of 0.011 m/s&middot;yr from 1955 to 1976, and the last stage shows a decreasing trend of 0.026 m/s&middot;yr from 1977 to 2000. The maximum reduction in winter monsoon velocity over the last 24 years (1977&ndash;2000) is approximately 20% of the average over the last 183 years (1918&ndash;2000). The variation of wind velocity shows two complete cycles over the past 183 years. In particular, the strongest and weakest winter monsoon velocities in the last two centuries occurred in the 1830s and 1940s, respectively. The variation in winter monsoon velocity in the 20th century is closely linked to the surface temperature of the South China Sea, as well as air temperature over continental China. In addition, the winter monsoon was weak during two warm periods, i.e. the 1940s and 1980s. Statistical analysis of the winter monsoon velocity anomaly as well as the El Ni&ntilde;o (warm event) and La Ni&ntilde;a (cold event) phenomena indicates that 70% of El Ni&ntilde;o events correspond to the weakness of the winter monsoon.</p

14C CHRONOSTRATIGRAPHY FOR QINGHAI LAKE IN CHINA

Radiocarbon accelerator mass spectrometry (AMS) techniques were used to date total organic carbon and plant seeds in the 1Fs core sequence (36&deg;48&prime;N, 100&deg;08&prime;E) from Qinghai Lake, China. This core was drilled ~18 m into Qinghai Lake sediments as part of an international cooperative research project, &ldquo;Scientifc Drilling at Qinghai Lake in the Northeastern Tibetan Plateau: High-Resolution Paleoenvironmental Records of Eastern Asia Linked to Global Change,&rdquo; which began in 2004. Based on the differences in lithology and total organic content (TOC) in core 1Fs, the core was divided into 3 sections for age-modeling purposes: the upper ~499 cm lacustrine silty clay to clay; the middle unit of silty clay with silt layers from 499&ndash;901 cm; and the lower 901&ndash;1861 cm silty clay, loess-like silt, and fne sand layers. Three different approaches are applied to the reservoir age problem. First, a simple linear regression gives an offset of 1342 yr. If the core is divided into three sections, linear regressions can be applied separately for the three segments, which results in an age estimate for the average hardwater effect of ~135 yr BP for the surface section up to 499 cm. If extrapolated for deeper sections, these results imply a higher reservoir offset for those two sections, which may be as much as 1143 and 2523 yr, but this assumes that there are no discontinuities in the core. A third approach using a wiggle-matching approach gave an offset of 196 yr. This study concludes that the reservoir age of Qinghai Lake is complex, but these new data add to our understanding of the 14C chronology of Qinghai Lake for the last 32 ka.</p

Peatland development and climate changes in the Dajiuhu basin,central China, over the last 14,100 years

Peatlands are one of the optimal archives for paleoclimate research and their records contain a detailed history of climatic and environmental variations during their formation. Here we collected a peat profile from the Dajiuhu basin in central China and analyzed several geochemical proxies, such as Total Organic Carbon (TOC), Total Nitrogen (TN), Titanium (Ti) and Aluminum (Al), to investigate the history of peat development. The results show that the peat growth was initiated after around 12.8 cal ka BP at the sampling site and the TOC and TN contents kept stable during the Holocene except during the periods of 10.5&ndash;9.0 cal ka BP and recent 1.5 cal ka BP. However, compared with other TOC records in the Dajiuhu basin, the history of peat development varied greatly in different sampling sites, indicating that the peat development in the Dajiuhu basin probably responds to both climate changes and local geological and hydrological conditions. Investigations of the interactions between climate change and peat development record in this study suggest that peat development presented significant responses to the large and rapid decreases in East Asian Summer Monsoon intensity, such as the 9.2 ka monsoon weakening event. However, the obvious long-term decreasing trend of monsoon precipitation during the mid-late Holocene did not lead to the degradation of the Dajiuhu peat, probably resulting from relatively stable temperature. In addition, the sharp decrease of TOC and TN values in the surface 15 cm of Dajiuhu peat was probably attributed to increased human activity.</p

Determination of Low Level 129I in Soil Samples Using Coprecipitation Separation of Carrier Free Iodine and Accelerator Mass Spectrometry Measurement

The accurate determination of ultra low level (129)I in sample is critical and essential for the application of natural (129)I in geological dating and environmental tracer studies. In this work, iodine was first separated from soil by combustion at high temperature; the released iodine was collected in an alkali trap solution. AgI-AgCl coprecipitaiton was used to separate carrier free iodine from the trap solution and to prepare target. (129)I in the target was then measured using a 3. 0 MV accelerator mass spectrometer. The recovery of iodine during the combustion is higher than 95%. An iodine recovery of about 75%-85% was obtained in the coprecipitation and the total recovery of iodine is above 70%. The developed method has been successfully used to determine (129)I in soil sample with low iodine content. A (129)I/(127)I atomic ratio as low as 10(-11) in the deep soil has been determined. The determination of (129)I/(127)I was ratio down to 10(-12) in solid samples.</p

A climate threshold at the eastern edgeof the Tibetan plateau

Proxy records of summer monsoon moisture at Lake Qinghai on the northeastern Tibetan Plateau reveal a late Quaternary climate history that is subtly different from that of speleothems from southern and eastern China. Total organic carbon and authigenic carbonate in two independently analyzed and dated cores indicate (1) relative stability and aridity during the glacial interval, (2) small variations during the B&oslash;lling-Aller&oslash;d and the Younger Dryas intervals, (3) comparatively abrupt change at the late Pleistocene/Holocene transition, and (4) relatively high variability during a wet early Holocene. Taken together, the data suggest that a climate threshold exists for penetration of Asian monsoon rainfall onto the Tibetan Plateau, a threshold that was crossed at the beginning of the Holocene. Conceptually, the threshold simply may be related to the topographic barrier that the eastern margin of the Tibetan Plateau presents to the landward penetration of the monsoon, or it may be related to nonlinearities in the climate system itself, such as sudden shifts in the configuration of the Westerly jet stream. Different mechanisms for producing a threshold are not mutually exclusive and may have combined to affect the dynamics of the Asian monsoon. In any case, the threshold is related to the presence of the Tibetan Plateau, which has a profound influence on the Asia monsoon system.</p

Reconstructing surface ocean circulation with 129I time series recordsfrom corals

The long-lived radionuclide 129I (half-life: 15.7&nbsp;&times;&nbsp;106&nbsp;yr) is well-known as a useful environmental tracer. At present, the global 129I in surface water is about 1&ndash;2 orders of magnitude higher than pre-1960 levels. Since the 1990s, anthropogenic 129I produced from industrial nuclear fuels reprocessing plants has been the primary source of 129I in marine surface waters of the Atlantic and around the globe. Here we present four coral 129I time series records from: 1) Con Dao and 2) Xisha Islands, the South China Sea, 3) Rabaul, Papua New Guinea and 4) Guam. The Con Dao coral 129I record features a sudden increase in 129I in 1959. The Xisha coral shows similar peak values for 129I as the Con Dao coral, punctuated by distinct low values, likely due to the upwelling in the central South China Sea. The Rabaul coral features much more gradual 129I increases in the 1970s, similar to a published record from the Solomon Islands. The Guam coral 129I record contains the largest measured values for any site, with two large peaks, in 1955 and 1959. Nuclear weapons testing was the primary 129I source in the Western Pacific in the latter part of the 20th Century, notably from testing in the Marshall Islands. The Guam 1955 peak and Con Dao 1959 increases are likely from the 1954 Castle Bravo test, and the Operation Hardtack I test is the most likely source of the 1959 peak observed at Guam. Radiogenic iodine found in coral was carried primarily through surface ocean currents. The coral 129I time series data provide a broad picture of the surface distribution and depth penetration of 129I in the Pacific Ocean over the past 60 years.</p

Global Monsoon Dynamicsand Climate Change

This article provides a comprehensive review of the global monsoon that encompasses findings from studies of both modern monsoons and paleomonsoons. We introduce a definition for the global monsoon that incorporates its three-dimensional distribution and ultimate causes, emphasizing the direct drive of seasonal pressure system changes on monsoon circulation and depicting the intensity in terms of both circulation and precipitation. We explore the global monsoon climate changes across a wide range of timescales from tectonic to intraseasonal. Common features of the global monsoon are global homogeneity, regional diversity, seasonality, quasi-periodicity, irregularity, instability, and asynchroneity. We emphasize the importance of solar insolation, Earth orbital parameters, underlying surface properties, and land-air-sea interactions for global monsoon dynamics. We discuss the primary driving force of monsoon variability on each timescale and the relationships among dynamics on multiple timescales. Natural processes and anthropogenic impacts are of great significance to the understanding of future global monsoon behavior.</p