Börtlüce Cave: A Natural Archive Linking Earthquakes, Volcanism, Climate Variability, and Human History in Western Türkiye

Börtlüce Cave (Manisa) in western Türkiye has a unique geographical location, which is a transition zone between tropical and polar atmospheric circulation systems, increasing its climate sensibility, and is a tectonically active region generating significant earthquakes, and lastly close to Kula Volcanic Field with remarkably well-exposed young volcanic structures. The cave is surrounded by significant archeological settlements, such as the ancient city of Sardis in Salihli, the capital of the Lydian Kingdom in the Bronze Age, where fossil footprints in volcanic ashes dated back to 4700 years ago (Ulusoy et al., 2019). Potential speleothem records from this cave therefore provide a valuable opportunity to explore paleoenvironmental changes in detail and to better understand how human populations responded to such changes.

Employing state-of-the-art methods, including U-Th dating, stable isotope (δ¹⁸O and δ¹³C), and trace element analyses, enables high-resolution and reliable reconstructions of hydroclimate variability, environmental evolution, and the effects of volcanic activity and earthquake-induced processes on cave environments.

Here we present initial records from two Börtlüce Cave stalagmites, reflecting changes in the stalagmite growth such as abrupt surface steps, growth axis deviations, and growth interruption. First results indicate that the occurrence of pronounced hiatuses in the underlying layers in stalagmites, accompanied by changes in fabric/stratigraphy and growth orientation, are consistent with seismic disturbance recurrences affecting drip hydrology rather than climatic forcing over the mid-late Holocene.

In addition to earthquake-induced changes, the isotope records from both stalagmites display similar isotopic patterns throughout the mid-late Holocene, indicating negligible kinetic fractionation effects in the cave. The δ¹⁸O values range between −7.4 and −4.2‰, while δ¹³C values vary from −9.3 to −3.7‰ along the growth axes of the stalagmites. Between 6 and 4 ka, both δ¹⁸O and δ¹³C values are depleted, reflecting wetter climatic conditions and enhanced soil biological activity.  After ~4 ka and until ~2 ka, isotope values become progressively more enriched in both stalagmites, indicating a transition to drier climatic conditions accompanied by reduced soil activity. Two distinct dry intervals are recorded, corresponding to the 4.2 ka Bond event and a second event at approximately 3.2 ka. These intervals likely represent significant hydroclimatic deteriorations that may have impacted regional human communities. Understanding their responses will provide valuable information for assessing current and future climatic hazards such as droughts.

Ongoing analyses of both stalagmites, together with expanded sampling of additional stalagmites from Börtlüce Cave, aim to produce a comprehensive reconstruction of paleoenvironmental changes related to climate dynamics, volcanic influences, and seismic activity, and to evaluate their combined impacts on the archaeological record.

References

Ulusoy İ., Sarıkaya M.A., Schmitt A. K., Şen E., Danisik M., Gümüş E., 2019. Volcanic eruption eye-witnessed and recorded by prehistoric humans. Quaternary Science Reviews, 212, 187-198.

Acknowledgement

This research was granted by the National Science and Technology Council, Taiwan, ROC (111-2116-M-002-022-MY3;114-2116-M-002-016-MY3), Academia Sinica (AS-TP-113-L04), and National Taiwan University Core Consortiums Project (113L891902). The authors are grateful to Kamil Altıparmak, Ali Karataş, Tuğberk Yetiş, Yiğit Karakuzu, Faruk Bilmez, and Kula Municipality for their assistance during the fieldwork. The authors thank Mehmet Oruç Baykara for his support.