The most important thorium-234 disequilibrium compilation you ever saw
Elena Ceballos-Romero and her colleagues (2022, see references below) propose a comprehensive global oceanic compilation of Thorium-234 (234Th) measurements that collects results from researchers and laboratories over a period exceeding 50 years. A total of 379 oceanographic expeditions and more than 56, 600 234Th data points compiled from over 5000 locations spanning all the oceans have been gathered in a single open-access, long-term, and dynamic repository. 234Th is a radioactive element naturally present in nature and is one of the most actively used tracers in oceanography it is included as one additional interest for GEOTRACES and is widely measured during GEOTRACES cruises. 234Th data from 17 cruises carried out in the frame of the GEOTRACES programme are included in the compilation. The data are archived on the repository PANGAEA® (Ceballos-Romero et al., 2021, see references below).
The authors also list a number of applications that could derive from this impressive data set, for example, giving an idea of the distribution of the probability of 234Th reaching equilibrium (or not) with its parent at 100 m. This distribution allows extracting i) the number of data points in the compilation that could be used to evaluate processes in the upper ocean such as export flux and export efficiency or ii) scavenging rates of trace metals or particle sinking velocities by using “deficit” ratios, as well as those that could be used to study processes such as particle remineralizations by using the “excess” ratios.
Figure: (a) Map showing the distribution of sampling stations catalogued as (i) unpublished (yellow diamonds), (ii) published exclusively in repositories (dark blue squares), and (iii) published in refereed journals (magenta dots). (b) Histogram of data points of 234Th/238U ratios at 100 ± 10 m of the water column. Ratios have been categorized as (i) “deficit” for those values whose 234Th concentrations are lower than 238U ones within 10% of uncertainty (ratio < 0.9), (ii) “equilibrium” for those values that have similar concentrations of 234Th and 238U (0.9 < ratio < 1.1), and (iii) “excess” for those values in which 234Th concentrations are in excess of 238U ones (i.e., ratios > 1.1). This figure can be interpreted as the distribution of the probability of 234Th reaching equilibrium (or not) with its parent at 100 m.
References:
Ceballos-Romero, E., Buesseler, K. O. and Villa-Alfageme, M. (2022) ‘Revisiting five decades of 234Th data: a comprehensive global oceanic compilation’, Earth System Science Data, 14(6), pp. 2639–2679. Access the paper: 10.5194/essd-14-2639-2022.
Ceballos-Romero, E., Buesseler, K. O., Muñoz-Nevado, C., and Villa-Alfageme, M. (2021) ‘More than 50 years of Th-234 data: a comprehensive global oceanic compilation‘, PANGAEA. DOI: 10.1594/PANGAEA.918125.