Combined Use of Short-Lived Radionuclides (²³⁴Th and ²¹⁰Po) as Tracers of Sinking Particles in the Ocean

Radionuclides can provide key information on the temporal dimension of environmental processes, given their well-known rates of radioactive decay and production. Naturally occurring radionuclides, such as Th-234 and Po-210, have been used as powerful particle tracers in the marine environment to study particle cycling and vertical export. Since their application to quantify the magnitude of particulate organic carbon (POC) export in the 1990s, Th-234 and, to a lesser extent, Po-210 have been widely used to characterize the magnitude of the biological carbon pump (BCP). Combining both radionuclides, with their different half-lives, biogeochemical behaviors, and input sources to the ocean, can help to better constrain POC export and capture BCP dynamics that would be missed by a single tracer. Here, we review the studies that have simultaneously used Th-234 and Po-210 as tracers of POC export, emphasizing what can be learned from their joint application, and provide recommendations and future directions.