Cosmogenic Isotope Lab

My graduate studies have focused on the use of cosmogenic ¹²⁹I to characterize the source and migration of volatiles in arc volcanic systems. Because nearly 70% of the earth's iodine is found in marine sediments, it is likely that subducted sediments carry a portion of that iodine to the mantle and that it reemerges along with other volatiles in volcanic systems. Cosmogenic ¹²⁹I is particularly suited for determining the age of fluids and volatiles in active tectonic processes because its long half-life (15.7 Ma) permits the determination of iodine ages as old as 80 million years.

In order to collect samples with very little surface contamination and a high enough concentration of iodine to carry out the isotopic analysis of ¹²⁹I, we have relied heavily on the help of local electric utility companies in Central America where electricity is produced commercially from geothermal wells. These include ICE in Costa Rica, ENEL in Nicaragua, and CEL in El Salvador. The wells which we sampled generally had depths between 500 and 2000 meters with temperatures between 200 and 300^oC. Other sources included fumaroles, mudpots, hotsprings, and crater lakes.

In addition to iodine studies, we have also carried out analyses of geothermal samples at the Rochester Rare Gas Facility, both for major gas composition and the isotopic composition of the noble gases. These analyses help to further characterize potential sources of volatiles in geothermal systems. Major ion composition is determined in the Cosmogenic Isotope Laboratory with a Dionex BioLC ion chromatograph, and total bromine and iodine concentrations are carried out in the Rochester ICP-MS Laboratory. Samples are extracted in the Cosmogenic Isotope Laboratory and sent to PRIME Laboratory for ¹²⁹I analysis.

We are also presently involved in a variety of other projects related to migration of brines in association with hydrocarbons. These include a variety of geological environments including coal gas deposits of the Fruitland Formation, Colorado; offshore methane hydrate deposits of Blake Ridge (ODP 997); and methane cold-seeps in fore-arc regions of New Zealand and Japan. Another ongoing project has been the determination of global distribution of anthropogenic ¹²⁹I from human nuclear activities.

Ongoing interests include:

Migration of brines in active and paleogeothermal systems.
Use of ¹²⁹I as a tool in determining the source, migration and stability of methane hydrates.
Dewatering of the subducted slab in fore-arc regions, and it's influence on mass transport and global cycles.
Biotransport and bioavailability of iodine in tropical environments. Causes of iodine deficiency syndrome in developing countries.
The influence of geological events on the global iodine cycle. The relationship between the iodine cycle and the carbon and nitrogen cycles.

Sampling at the Otopotehetehe methane seeps, New Zealand