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

Elena Ceballos-Romero1, Ken Buesseler2, Cristina García-Prieto3 and Maria Villa-Alfageme1, (1)Universidad de Sevilla, Applied Physics II, Sevilla, Spain, (2)Woods Hole Oceanographic Institution, Department of Marine Chemistry & Geochemistry, Woods Hole, United States, (3)University of Sevilla (USE), Department of Applied Physics II, Sevilla, Spain
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 The compilation is made of 200 published datasets and 10 unpublished ones with sampling from approximately 5000 locations spanning all the oceans for total 234Th profiles, dissolved and particulate 234Th concentrations, and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.