Sierks, Maria; Paradis, Sarah; Roca-Martí, Montserrat; Puigcorbé, Viena; Puig, Pere (2025): Global database of sedimentary excess thorium-234 (Th-234) in and near submarine canyons [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.987505

This global compilation was generated to explore the application of thorium-234 (234Th) as a tracer for recent sedimentation in submarine canyons. Submarine canyons are located along the continental margins, including the shelf regions, which are disproportionally relevant for the carbon cycle and other essential biogeochemical processes. These geomorphological features can act as funnels for particles and represent a strong connection between land and the open ocean. The continental margins encompass dynamic environments, granting the necessity to use tracers capable of quantifying short-term events. 234Th is a particle reactive radionuclide that gets scavenged onto particles in the water column and, due to its short half-life of 24.1 days, it allows estimating the magnitude of recently deposited sediment on the seabed over the previous ~4 months. Excess 234Th (234Thxs) with respect to 234Th in secular equilibrium with its parent nuclide uranium-238 can be used to calculate excess 234Th inventories as a proxy of recent sediment deposition (Aller and Cochran, 1976). Moreover, the vertical profile of 234Thxs in surface sediment also serves for estimation of mixing rates when sedimentation rates are sufficiently low. This has advantages over the classic and extensively used lead-210 dating method with a decadal integration period (Arias-Ortiz et al., 2018), since the relatively short time scale of 234Th can match the occurrence of recent short deposition events, thus revealing the impacts of potential recent riverine runoff, trawling-derived deposition or phytoplankton blooms, among others.

To compile these data we conducted a search across Google Scholar (last accessed: 03-Sep-2025 ) for periods encompassing 1979-2025, and obtained 123 search results using the terms: (Excess 234Th OR Excess 234 Th OR Excess Th-234 OR Excess Thorium-234) AND (submarine canyon OR canyon OR off-shelf) AND (sediment core OR sediment samples OR core OR gamma spectrometry OR gamma spectroscopy OR gamma counting OR radiochemical analysis OR radioisotopic). After thorough inspection of the publications, those reporting sedimentary 234Th data in canyon environments were selected, resulting in a compilation of data from a total of 26 publications from 20 different canyons. Data on 234Thxs parameters, sampling methodology, and contextual information of sediment cores obtained in submarine canyon environments were carefully extracted using the information given in the main text, tables, figures, and supplementary files. Latitude, longitude and sampling dates were assigned to the midpoint or the sampling month when not explicitly stated. Gamma spectrometry was applied as the counting method, with one exception measured by beta counting. Empty cells represent missing data. In 12 studies, data was also provided from the shelf, slope or abyssal plain near the canyon. The compilation includes surface 234Thxs activities, 234Thxs penetration depths, 234Thxs inventories and mixing rates (Db) from canyon studies with coring sites inside canyons, spanning a depth range from 120 to 4280 m and, additionally, near those canyons. In canyons, the most frequently provided parameter is the surface 234Thxs activity (19 of 26 studies) ranging from 20 to 4040 Bq kg-1with a mean value of 520 Bq kg-1. 10 of 26 studies reported 234Thxs inventories, showing high variability with a range of values between 10 and 50700 Bq m-2 and a mean value of 2860 Bq m-2. 10 of 26 studies reported (or provide enough data for extraction of) 234Thxs penetration depths (mean of 2 cm, ranging from 0.4 to 24 cm). The least frequently reported 234Thxs parameter is mixing rate (6 of 26 studies) yet encompassing a large range of values from 0.2 to 68.7 cm2 y-1 with a mean of 6.9 cm2 y-1.This database provides an overview of the variability of recent sediment deposition patterns as well as other sedimentary parameters derived from 234Th measurements across canyons distributed globally. Advancing the characterization of short-term sedimentary signatures using 234Th is promising and relevant in canyon environments, which represent a crucial link in the land-ocean interface.