HR: 0800h
AN: OS11B-0506    [Abstracts]
TI: Flow-Through Leaching of Marine Barite: New Insights on its Composition and Diagenesis
AU: * Hsieh, C
EM: chsieh@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States
AU: Torres, M E
EM: mtorres@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States
AU: Ungerer, A
EM: aungerer@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States
AU: Klinkhammer, G P
EM: gklinkhammer@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States
AB: The distribution of stable mineral barite (BaSO4) in marine sediments has long been studied as a proxy for paleoproductivity. It is important to investigate the variation in Sr/Ba ratios of crystal barite, as it has a great influence on barite solubility and its early diagenetic processes. In addition, the role of alternative barium carriers to the sediments (e.g. aluminum silicates and oxyhydroxides) and their contributions to overall barium budget and burial efficiency need to be resolved. The techniques currently used to describe and quantify barium phases are all based on batch leaching techniques that define barium phases operationally, not chemically. Because during batch analyses each phase is characterized by a single-point measurement, variations due to phase heterogeneities cannot be resolved; nor can the results of these experiments be related in any systematic way to what happens in nature. To overcome this problem, we are developing a flow-through method that makes use of automated chromatographic techniques, which allows complete monitoring of the dissolution of barite samples with time-resolved analysis (TRA) as each phase is sequentially leached using different reagents. We have analyzed a barite sample recovered from seeps along the San Clemente escarpment, and show that we can attain complete dissolution of the sample (>85%) in 2 hours, using DTPA at 80°C. Approximately 100 μg of barite are first leached with distilled water (pH 5) for 30 minutes. During this step ~2% of the barite is removed. This highly soluble phase has Sr/Ba ratios that range from 30 to 120 mmol/mol. Acid leaching of the samples with 10 mM HNO3 removes an additional 4~8% of the barite, and this phase has Sr/Ba ratios ranging from 13 to 35 mmol/mol. Higher acid concentration (100 mM HNO3) dissolves up to 40% of the barite. These results are consistent with electron microprobe data that show clear oscillatory zoning of the (Ba,Sr)SO4. Unlike the barite sample, sediment samples collected at the base of the escarpment did not show a Ba release in the water leach. We might speculate that the highly susceptible Sr-rich barium phase present in the barite sample, dissolved during transport from a seep site leaving a barite with a lower Sr/Ba ratio, as found in the sediment samples. Our analytical approach has the potential to further address a variety of outstanding questions on the complex geochemical cycle of barium and its applications to climate change, upper ocean fertility and ocean circulation through time.
DE: 1042 Mineral and crystal chemistry (3620)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1065 Major and trace element geochemistry
DE: 1094 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting