Revisiting five decades of Th-234 data: a comprehensive global oceanic compilation

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ceballos-Romero, E., Buesseler, K. O., & Villa-Alfageme, M. Revisiting five decades of Th-234 data: a comprehensive global oceanic compilation. Earth System Science Data, 14(6), (2022): 2639–2679, https://doi.org/10.5194/essd-14-2639-2022.We present here a global oceanic compilation of 234Th measurements that collects results from researchers and laboratories over a period exceeding 50 years. The origin of the 234Th sampling in the ocean goes back to 1967, when Bhat et al. (1969) initially studied 234Th distribution relative to its parent 238U in the Indian Ocean. However, it was the seminal work of Buesseler et al. (1992) – which proposed an empirical method to estimate export fluxes from 234Th distributions – that drove the extensive use of the 234Th–238U radioactive pair to evaluate the organic carbon export out of the surface ocean by means of the biological carbon pump. Since then, a large number of 234Th depth profiles have been collected using a variety of sampling instruments and strategies that have changed during the past 50 years. The present compilation is made of a total 223 data sets: 214 from studies published in either articles in refereed journals, PhD theses, or repositories, as well as 9 unpublished data sets. The data were compiled from over 5000 locations spanning all the oceans for total 234Th profiles, dissolved and particulate 234Th activity concentrations (in dpm L−1), and POC:234Th ratios (in µmol dpm−1) from both sediment traps and filtration methods. A total of 379 oceanographic expeditions and more than 56 600 234Th data points have been gathered in a single open-access, long-term, and dynamic repository. This paper introduces the dataset along with informative and descriptive graphics. Appropriate metadata have been compiled, including geographic location, date, and sample depth, among others. When available, we also include water temperature, salinity, 238U data (over 18 200 data points), and particulate organic nitrogen data. Data source and method information (including 238U and 234Th) is also detailed along with valuable information for future data analysis such as bloom stage and steady-/non-steady-state conditions at the sampling moment. The data are archived on the PANGAEA repository, with the dataset DOI https://doi.org/10.1594/PANGAEA.918125 (Ceballos-Romero et al., 2021). This provides a valuable resource to better understand and quantify how the contemporary oceanic carbon uptake functions and how it will change in future.This work was partially funded by the V Research Programme from the Universidad de Sevilla (Elena Ceballos-Romero) and EU FEDER-Junta de Andalucía funded project US-1263369 (María Villa-Alfageme). Ken O. Buesseler was supported in part by NSF under GEOTRACES, NASA as part of the EXPORTS program, and WHOI as part of the Ocean Twilight Zone project. María Villa-Alfageme and Ken O. Buesseler are also part of an IAEA Coordinated Research Project “Behaviour and effects of natural and anthropogenic radionuclides in the marine environment and their use as tracers for oceanographic studies