AbstractWe conducted an intercomparison of methods for the determination of 234Th in seawater. Samples were collected either from a shore-based 600 m water source, or from standard bottle casts collected in deep waters off Hawaii and in the Southern Ocean. We compared large volume techniques which rely upon Mn cartridges for the collection of dissolved 234Th and its detection via gamma counting (>200 liter samples) with small volume methods that employed either direct beta counting, or beta counting after radiochemical purification (2-20-Liter samples). Unique to this study are the presentation of a novel 2 and 5 liter 234Th methods. This new method is an adaptation of 20-liter methods which are based on a coprecipitation of thorium with Mn oxides and the direct beta counting of the precipitate. These Mn coprecipitation methods were found to be superior to other methods due to ease of sample collection and processing and low overall analytical uncertainties.