SCAVENGING AND TRACKING OF RADIOISOTOPE PARTICLES IN ENVIRONMENTS (S.T.R.I.P.E.): A PILOT STUDY

Scientific advancements in isotope geochemistry and sedimentary geochronology have allowed for high-resolution sampling of radioisotope activities in marine sediments. Given the recent advances in deep sea mining, the ability to understand the nature of radioisotope scavenging on resuspended sediments could provide essential insights into the impacts it may have on benthic environments. Sediment plumes from collector vehicles used in deep sea mining often spread their footprint over the seafloor and sensitive indicators such as radioisotopes are critical to their further investigation. This pilot study attempts to replicate the natural process of radioactive isotope scavenging of resuspended sediments in a laboratory setting. Radioisotopes, such as ²¹⁰Pb and ²³⁴Th, are valuable tools for evaluating human and natural impacts recorded in the sediment record. Radioisotopes adsorb to sediment particles and remain until they are deposited on the ocean floor and begin to decay. The known decay rate of ²³⁴Th and ²¹⁰Pb allows for the calculation of a date of deposition and also for the determination of the spatial extent of the resuspended sediment in the surface sediments.

A tank replicating the deep sea sedimentary environment was constructed for this study and filled with 4.5kg of sediment. This sediment was known to have been deposited over 100 years ago, thereby no longer showing any excess radioisotope activity. Roughly 100 liters of seawater flowed through the tank at one liter per minute as the sediments were resuspended every twenty minutes for thirty-second intervals. Gamma spectrometric analysis of post-experiment samples revealed that ²³⁴Th adsorbed to the resuspended sediment during the experiment and supported the constant rate of supply age model. Results from the radioisotope ²¹⁰Pb, however, were inconclusive and require further testing.

This pilot study only scratches the surface of the questions about the implications of resuspended radioisotope adsorption in deep sea settings. Radioisotope scavenging has high utility for determination of the spatial extent of ambient sediment plumes caused by deep sea mining. Further research into methods of artificial resuspension and adsorption are critical to fully understanding this process.