Revisiting 45 years of 234Th data: a comprehensive global oceanic database

The ²³⁴Th-²³⁸U radioactive pair has been extensively used to evaluate the efficiency with which photosyntetically fixed carbon is exported from surface ocean by means of the biological pump since the 90`s. The seminal work of Buesseler et al. (1992)* proposed that particulate organic carbon (POC) flux could be calculated from ²³⁴Th distributions if the ratio of POC to ²³⁴Th measured on sinking particles (POC:²³⁴Th) at the desired depth was known. Since then, a huge amount of ²³⁴Th depth profiles have been collected using a variety of sampling instruments and strategies that have changed along years.

We present here a global oceanic database of ²³⁴Th measurements that compiles results from innumerable researchers and laboratories over a period exceeding 40 years. The compilation is made of 200 published datasets and 10 unpublished ones with sampling from approximately 5000 locations spanning all the oceans for total ²³⁴Th profiles, dissolved and particulate ²³⁴Th concentrations, and POC:234Th ratios (both from pumps and sediment traps) for two sizes classes (1-53 um and < 53 um) when available. Appropriate metadata have been included, including geographic location, date, and sample depth, among others. When available, we include water temperature, salinity, ²³⁸U data and particulate organic nitrogen data. Data originator information (including total and particulate ²³⁴Th methodology) are also included along with valuable information for future data analysis such as bloom stage and steady/non-steady state conditions at the sampling moment.

This undertaking is a treasure of data to better understand and quantify how the contemporary oceanic carbon uptake functions and how it will change in future. We provide here an introduction to the dataset along with some key graphics and an overview of its future use. Open access will be given to the compilation for a collective use, encouraging authors to collaborate on its expansion by including new ²³⁴Th datasets from here on.

*Buesseler, K., M. Bacon, K. Cochran, H. Livingston (1992). Carbon and nitrogen export during the JGOFS North-Atlantic bloom experiment estimated from Th-234u-238 disequilibria. Deep-Sea Research Part a-Oceanographic Research Papers, 39(7-8), 1115–1137.