Browsing by Subject "iodine"
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Item Speciation and transport of anthropogenic 129Iodine and natural 127Iodine in surface and subsurface environments(Texas A&M University, 2005-02-17) Schwehr, Kathleen AnnIodine is a biophilic element with one natural long-lived isotope, 129I (t1/2= 15.6 million years), and one stable isotope, 127I. The inventory of 129I in surface environments has been overwhelmed by anthropogenic releases over the past 50 years. The objective of this study is to utilize the elevated concentration and biophilic nature of 129I and the isotopic ratio of iodine (129I/127I) as a tracer of water mass movement and organic matter. Additionally, the significantly elevated values of 129I/127I could provide a geochronometer, similar to the way 14C is used, particularly for terrestrial organic matter that is less than 50 years old. A series of laboratory experiments and field investigations were carried out to characterize the dominant chemical forms of dissolved iodine, i.e., iodide (I-), iodate (IO 3-), and organic iodine (DOI) in natural waters. Sensitive methods were developed for the analysis of nanomolar quantities of 127I species in a variety of environmental systems using high performance liquid chromatography (HPLC) and an organic iodine decomposition technique, dehydrohalogenation. The potential use of 129I/127I as a hydrological tracer was evaluated through measurements of 129I and 127I, which were carried out in wells in the artificially recharged ground water basin of Orange County, California. Literature values of aquifer ages based on 3H/3He and δ18O tracer data, as well as time-series data of chloride and Santa Ana River flow rates over the past decade were compared to values for 129I and 127I. The iodine isotopes demonstrated a conservative behavior in these aquifers, suggesting that the observed variations of these isotopes reflect past river flow conditions during the time of recharge. The feasibility of using 129I/127I ratios to trace terrestrial organic matter across an estuary was tested. A novel analytical technique to determine 129I/127I ratios in DOI was developed for this investigation. The results of a Galveston Bay transect clearly show that 129I/127I ratios in DOI can remain elevated up to salinity of about 15, but that 129I/127I values of inorganic iodine species do not show any trend with change in salinity gradient due to fast isotopic and chemical equilibration in the estuarine waters.Item Validating Annual Growth Bands of Deep-Sea Black Corals and Calculating Ocean Reservoir Ages from the Gulf of Mexico and Southeastern United States(2014-08-13) Mohon, Leslye MDeep?sea black corals have been found to be long-lived and grow in a tree like fashion depositing rings in their skeleton that have been suggested to be annual growth bands. Iodine was used in this study to develop a novel dating method to measure the life spans and growth rates of these black coral, Leiopathes sp. The visual growth band count dating method was conducted on three of the GOM specimens and resulted in life spans ranging from 490 ?50 to 1315 ?130 years with growth rates ranging from 11 ?3 to 16 ?2 ?m yr-1. The iodine dating method resulted in life spans of 630 ?65 to 1240 ?125 years and growth rates ranging from 10 ?1 to 19 ?3 ?m yr-1. The life spans and growth rates that resulted from the counting of iodine peak generally matched the radiocarbon results, which yielded life spans of 620 ?40 to 2040 ?40 Cal yr. BP (before present 1950). The new iodine dating method in conjunction with radiocarbon and visual ring counts from SEM images validated the annual growth bands in the deep-sea black coral Leiopathes sp. from the GOM and SEUS. Using the independent (iodine) age models in conjunction with the radiocarbon records, ocean reservoir age records can be developed for the last ~500 to 1000 years. These findings provide a rare continuous record through time of highly variable reservoir ages suggestive of changing ocean dynamics in association with climatic events in the late Holocene. The preferred explanation for the variability found in these reservoir ages is that the changes in the reservoir ages reflect changes in the strength of the Yucatan current. This study is the first to validate that the rings deposited in the skeleton of deep-sea black corals, Leiopathes sp., are annual growth bands and that peaks in iodine counts associated with the growth band can be used as an independent dating method if good quality thin sections are made before analyses are conducted.