Lake-level fluctuations from Lake Iznik seismic stratigraphy (NW Turkey): Implications for past climate.

Understanding past water-level changes are essential to human development. Changes in lake levels can result in the displacement of populations due to rising water levels, or be a limiting factor in the case of irrigation for agriculture or in terms of water resources. Lake-level fluctuations can be the consequence of outlet modification, human activity, or on a longer time scale, of climatic change or tectonic activity.

In Turkey, several studies showed that the water level of numerous lakes significantly changed since the Last Glacial Maximum (LGM). Here, we present the history of Lake Iznik (83 m above sea level) which is the fifth-largest lake in Turkey. Based on high-resolution seismic profiles, sediment cores and bathymetry, we document new insights into its lake-level variations since the late Pleistocene. An important transgressional phase with a highstand (> 50 m above the modern lake level) of uncertain age is documented during the late Pleistocene, preceding the LGM (> 40 ka BP). Before this highstand, the lake level was substantially lower by at least ~ 60 m. The stepwise transgression that led to this highstand is associated with the formation of a series of up to 13 buried paleoshorelines. This phase of high lake level is followed by a sedimentation pattern marked by strong lateral differences in sediment accumulation in the northern part of the lake. These pronounced lateral differences are partly caused by lacustrine contourite drifts due to strong currents, or by prograding delta clinoforms. The younger phases (< 18 ka BP) are characterized by different regressional/transgressional cycles with a major lowstand at ~ 50 m below the present-day lake level during the early Holocene, probably related to a dryer climate. Today, the lake level continues to fluctuate as shown by one of the most important archaeological discoveries of this decade. During a 2014 aerial photo survey, the fourth to fifth century CE St. Neophytos Basilica was discovered underwater in Lake Iznik, 20 m from the shore at an average depth of 2 m (e.g. Şahin & R. Fairchild, 2018). However, it is more difficult to distinguish anthropogenic from climatic influences in recent times.

Reference: Şahin, M., & Fairchild, M. R. (2018). Nicea's underwater basilica. Biblical Archaeology Review, 44(6), 30–37.