Evolution of lagoon formation and desiccation along the southeast Caspian coast: A historical and modern perspective

ABSTRACT The southeastern Caspian coast, a climate transition zone from subtropical to arid conditions and host to several Ramsar wetlands, is highly sensitive to Caspian sea‐level (CSL) fluctuations and climate change. This study investigates the environmental evolution and resilience of the Gomishan Lagoon by integrating paleoenvironmental archives, instrumental observations, re‐analysis data sets, satellite imagery, and future climate projections. The objectives are to decipher the past CSL changes on lagoon development and to evaluate the capacity of this coastal system for self‐restoration under past CSL fluctuations, assess whether this capacity persists under the current phase of rapid CSL decline, and infer its likely future trajectory. Results indicate that CSL variability over the past century comprised complete rise–fall cycles, with the present decline initiating a renewed phase of lagoon desiccation. A ~2.5 m CSL fall since 1996, coupled with rising air temperatures, has accelerated desiccation of the Gomishan Lagoon. By 2023, the extent of desiccation exceeded that observed in 1978 despite comparable CSL, reflecting enhanced sediment infilling. Sedimentary successions preserve evidence of historical lowstands, including desiccation phases during the Sasanian period of late Antiquity (ca. 400–450 AD), the Medieval Period (~1000 AD), and around 1600 AD, accompanied by progressive seaward displacement of the lagoon during regressive phases. Relict beach ridges and back‐barrier depressions further indicate repeated lagoon formation along the southeastern Caspian coast throughout the Holocene. During highstand periods, lagoon capacity in organic material burial and carbon accumulation increased threefold compared to the lowstand periods. Although projected warming is expected to intensify stress on existing wetlands, the combined geomorphological and sedimentological record suggests that, under natural conditions, new lagoons are likely to form seaward, highlighting the multidcadal adaptability of this coastal system under changing climate and sea‐level conditions.