Welcome to the ²³⁴Th Conference Home Page

Future Applications of ²³⁴Th in Aquatic Ecosystems

(FATE)

The FATE conference was held from August 16-19^th, 2004 at the Woods Hole Oceanographic Institution.  Over 40 national and international scientists participated in discussions on key issues ranging from sample collection to future collaborative expeditions.  Results from the meeting will soon be distributed to the wider oceanographic community via an EOS article and five seminal papers on:  New methodologies and techniques for ²³⁴Th analysis, Estimating carbon export using C/²³⁴Th ratios, Modeling ²³⁴Th export using 1D to 3D models, ²³⁴Th speciation in seawater, and Future applications.

Why have a meeting?

One of the many questions facing oceanographers today involves understanding the 'carbon budget' in a comprehensive and quantitative sense. This entails describing the suite of fluxes of carbon and associated nutrients and trace metals from the surface ocean to depth. The removal or "export" of carbon from the euphotic zone, is at least partly replenished by drawdown of atmospheric CO₂ (Falkowski et al. 2000). Thus, knowledge of export production and its variability is important for assessing the role of the world's oceans in sequestering atmospheric CO₂. Nonetheless, one of the most elusive parameters of the carbon budget remains the spatial and temporal magnitude of particle export (Doney 1999). "Sinking particle flux" within the carbon system has raised the stakes considerably in terms of data sampling and comparison, and each major research program from pre-Vertex to post JGOFS has struggled to find new ways to determine this important parameter.

There are two methods that are most often used to specifically measure particle export from the upper ocean: sediment traps and ²³⁴Th:²³⁸U disequilibrium. Sediment traps are the most commonly used technique in oceanographic research for the collection and quantification of settling particle fluxes. In spite of their wide use, there are concerns about their ability to quantitatively collect unbiased samples of settling particles (Gardner 1996). For example, several studies have found that traps deployed at the base of the photic zone are subject to current velocities that may be quite high (Butman 1986; Gust and Kozerski 2000). Furthermore, there are issues associated with contamination from "swimmers" and solubilization of both inorganic and organic matter within the traps that may contribute to additional uncertainties in flux data (Forbes et al. 1992; Kähler and Bauerfeind 2001; Michaels et al. 1990; Noji et al. 1999).

Although a powerful tool, there are still a number of questions regarding the interpretation of ²³⁴Th disequilibrium. As a result, the ²³⁴Th community has inherited many of the same disputes of the sediment trap community: How best to estimate sinking particle flux? There are now questions regarding ²³⁴Th speciation, reactivity, sample collection and analysis, and modeling (Benitez-Nelson et al. 2001a; Benitez-Nelson et al. 2001b; Buesseler et al. 1995; Buesseler et al. 2001; Buesseler and Charette 2000; Guo et al. 2002; Kim et al. 1999; Moran et al. 2003; Quay 1997; Quigley et al. 2001; Quigley et al. 2002). These issues introduce uncertainty and debate regarding the appropriateness of using ²³⁴Th as an in-situ tracer for the export of particulate organic carbon (POC) and associated biogenic and other particle reactive elements. Understanding these issues are paramount if ²³⁴Th is to be successfully used as a proxy for particle cycling and flux by the oceanographic community. Thus, it is time for the ²³⁴Th community to come together to help resolve these questions and to coordinate a specific plan that would help answer the above questions in a more timely and efficient manner.

The purpose of the workshop was to bring together a number of international experts in the collection and application of ²³⁴Th in aquatic ecosystems with diverse opinions and backgrounds to discuss and define current ²³⁴Th issues and to devise a coherent strategy as to how to resolve them.

This meeting was sponsored by the Chemical Oceanography Program of the National Science Foundation and the Scientific Committee for Oceanic Research.

Last Updated August 2004 by C. Benitez-Nelson