A new hydrological climatic proxy in arid lake sediments: Iodine‑uranium concentrations

Hydrological variation in the past ∼2 kyr is important for understanding the impact and driving forces of climate changes in the present and future, especially in arid areas. Sediment is one of the most useful archives in such a time period, and selection and validation of qualified hydrological proxies is the key point for reconstruction of hydrology in the past centuries. However, such research still faces a challenge due to limited knowledge of physiochemical implications of the traditional proxies in the specific lake, and difficulties to discriminate dry-wet from warm-cold signals. Here, a sediment core collected from Keluke Lake, Qaidam Basin, Northwest China was analyzed for iodine and uranium concentrations, to explore their potential as a new hydrological proxy in the arid regions for reconstructing the dry-wet changes during the past ∼2200 years. A significant correlation between iodine and uranium concentrations (r = 0.62, P < 0.01) was observed in the sediment core, and four peak events of synchronously varied iodine and uranium concentrations occurred in the studied sediment core. This indicates similar physiochemical behaviors of the two elements from the catchment to the sediments via lake water. During drier periods, as vegetation degradation and soil organic substance content decreased, water-soluble iodine and uranium were intensively leached, and fine particle associated iodine and uranium were seriously eroded from catchment soils. Meanwhile, the suspended matter concentrations and organic substance content in lake water increased as well, which facilitated more iodine and uranium to be deposited and recorded in the sediment as peak events. The four dry events coincide with the reported climatic changes in other lake sediments, ice core and aeolian sediments, and also correspond with the society evolution in this area, including the establishment of Tuyuhun Kingdom (313–663 CE), Tubo Empire (618–842 CE), Mongolian tribes (1495–1591 CE, and the Han population immigration driven by a severe drought disaster in 1876–1879.