A review of present techniques and methodological advances in analyzing 234Th in aquatic systems

The short-lived thorium isotope Th-234 (half-life 24.1 days) has been used as a tracer for a variety of transport processes in aquatic systems. Its use as a tracer of oceanic export via sinking particles has stimulated a rapidly increasing number of studies that require analyses of Th-234 in both marine and freshwater systems. The original Th-234 method is labor intensive. Thus, there has been a quest for simpler techniques that require smaller sample volumes. Here, we review current methodologies in the collection and analysis of Th-234 from the water column, discuss their individual strengths and weaknesses, and provide an outlook on possible further improvements and future challenges. Also included in this review are recommendations on calibration procedures and the production of standard reference materials as well as a flow chart designed to help researchers find the most appropriate Th-234 analytical technique for a specific aquatic regime and known sampling constraints. (c) 2005 Elsevier B.V. All rights reserved.