Pure and Applied Geophysics

Tkach, Alina; Tkach, Nikolai

doi: 10.1007/s00024-025-03670-wpmid: N/A

This study compares the previously published high-resolution bulk carbonates oxygen isotope composition with the new ostracod δ18O data obtained from the same GS19 core in the Central Caspian basin. The study reveals a notable contrast between the two isotopic records, confirming the previously proposed hypothesis that the bulk carbonate record of the core was significantly affected by the terrigenous discharge from the catchment area, resulting in a dilution of the paleoclimatic signal. The isotopic composition of ostracod shells has been demonstrated to be an accurate and valuable proxy for climate change. It appears that the ostracods examined may also be highly sensitive to the influx of river water, whereas the ostracod isotope composition reflects long-term hydroclimatic trends. By integrating the δ18O data with environmental and sedimentological data from the Caspian Sea region, three stages of the evolution of the Central Caspian Sea have been identified within the time interval recorded in the sedimentary sequence of the studied core. The initial stage was identified as corresponding to the end of the transition from the Late Glacial period to the Holocene. The second stage is associated with the Mangyshlak lowstand. It is proposed that the Central Caspian Sea responded to an increase in heat supply and aridity during the early Holocene. The high degree of isotopic enrichment of both Caspian Sea waters and ostracod valves is reflective of the highly arid environment and higher water salinity. The final and third stage is associated with the Neocaspian transgression, which exhibits complex internal dynamics.