Climate Control of Iodine Isotopic Composition Evidenced by Argentine Entisols Records

The long half-life of 129I makes it useful for dating marine sediments aged 2-90 Ma. However, the lack of initial value dating hinders its application for dating terrestrial sediments. A large scatter of 129I/127I in prenuclear terrestrial samples has been reported; however, the key influencing factors remain unclear. This study presented iodine isotope data from three Argentine Entisol profiles and developed an iodine-source model to determine the influence of the source on iodine isotopic composition. The temporal patterns demonstrated clear climate modulations in natural terrestrial iodine isotopes over the last similar to 15 Kyr. The model identified rock weathering as a major source of iodine in continental sediments. Higher 129I/127I ratios at mid-high latitudes arise from weak geomagnetic shielding of cosmic rays and thus a high production rate, implying limited meridional diffusion of atmospheric iodine. These findings reveal that environmental factors are significant for constraining the initial value of terrestrial 129I. In terrestrial sediments, the absence of a specific initial value poses a challenge for 129I dating. Through examination of three profiles of Argentine Entisols, this study investigated how changes in the environment over the past 15 Kyr affected iodine isotopic composition. The climate modulations of iodine isotopes were indicated by comparing them with climatic proxies. A simple multi-source model of iodine suggested that "old" iodine from catchment rock weathering was a major iodine provider, and decreased 129I/127I with the enhanced South American Summer Monsoon and South Westerly Wind indicated a low-129I iodine input. The deviant 129I/127I of the most southern site was hypothesized to be caused by a greater cosmogenic 129I production rate at high latitudes than at mid-low latitudes. Natural 129I/127I was for the first time found to co-vary with the summer monsoon and westerlies in South America Rock weathering contributes more iodine to terrestrial sediments than oceanic emissions High 129I/127I values at mid-high latitudes imply low geomagnetic shielding and limited meridional diffusion of atmospheric iodine