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Overview


Ken Buesseler making espresso.

Café Thorium is not really a cafe although we have been known to serve espresso and latte throughout the worlds major ocean basins. In fact, we are a serious scientific research team in the Department of Marine Chemistry and Geochemistry at the Woods Hole Oceanographic Institution. Thorium is just one of many radioactive elements we measure. We analyze marine samples for both natural and artificial radionuclides. Examples of naturally occurring radionuclides include those isotopes produced in the decay chains of the long-lived uranium and thorium isotopes (such as thorium-234, lead-210, radium-226), and cosmogenically produced radionuclides such as beryllium-7 and phosphorus-32. The artificial radionuclides we study, such as cesium-137, strontium-90 and plutonium-239,240, were released during atmospheric nuclear weapons testing in the early 1960's or more recently, by the Chernobyl nuclear reactor accident in 1986.

By knowing their source term, geochemistry, and radioactive decay properties, we use radionuclides as in situ tracers of a wide variety of chemical, biological and physical processes. This page was designed with the both serious and not-so-serious science types in mind, so bear with us and let us know what you like, think you like, and just don't care about or understand and we'll try and make the next version more surfer friendly. Sit back with a cup of Java and browse away The people who pay for his work include: The National Science Foundation; the Office of Naval Research; the National Oceanic and Atmospheric Administration; the Department of Energy; the US Environmental Protection Agency; the Woods Hole Oceanographic Institution and the list goes on (you too can have YOUR NAME HERE!- click here to find out how!).

Upper Ocean Export derived from 234Th: Introduction and Overview


Thorium-234 (half-life = 24.1 days) was first measured in the oceans in the late 1960's by Bhat et al. when it was shown that 234Th concentrations, or activities, were lower near the continental margins and higher offshore. Thorium-234 is produced in the oceans via the decay of its long-lived and highly soluble "parent", 238U. The activities of these two radionculides reach secular equilibrium (i.e. are identical) at relatively shallow depths of 100-200m. Since 234Th chemistry dictates that it is highly particle-reactive, and hence sticks to all particle surfaces, the loss of 234Th from surface waters is a direct indication of the removal rate of material on sinking particles from the upper ocean. The link between biological processes in the upper ocean and the extent of 234Th removal was first clearly demonstrated in a series of papers by Coale and Bruland in the mid-80's, who proposed that a relationship existed between 234Th removal rates and primary and new production in the open ocean.

Though we have been working with radionuclides for a much longer time, the Cafe Thorium had its origin with the US Joint Global Ocean Flux Program (JGOFS). In 1988 we took part in the North Atlantic Bloom Experiment (NABE) in collaboration with Drs. Bacon and Livingston at WHOI and Cochran at the State Univ. of New York, Stony Brook. During this study a clear relationship was found between the onset of the spring phytoplankton bloom, the subsequent drawdown of nutrients and CO2, and the net removal of 234Th (Buesseler et al., 1992 in CV). From the 234Th data one could reliably estimate 234Th particle fluxes (essentially from the difference between 234Th production and decay rates). Furthermore, and fundamentally more interesting and new to biogeochemical studies, is that by measuring the ratio of particulate organic carbon (or PON) to 234Th on sinking particles, we showed that it is possible to empirically determine the export fluxes of POC and associated elements.

After the North Atlantic, the Cafe Thorium jumped into high gear, and we have now collected samples over much of the world's oceans on cruises totaling over one year at sea! For more information and specific results from these studies, and for updates on work in progress, explore the links on the side panel of this website.

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