Quantifying Quaternary climate variability in the Southern Caucasus using gastropod shell isotope transfer functions and climatic niche modeling

Subfossil gastropod assemblages preserved in geological deposits provide valuable archives to reconstruct past environmental and climatic conditions. We present new results from loess-palaeosol sequences in the Armenian Highlands that document multiple glacial-interglacial transitions over the past ~400 ka. The primary aim of this study is to generate quantitative palaeoclimate data suitable as reference data for the calibration of Earth system models. Our approach combines stable oxygen isotope analysis (δ¹⁸O) of gastropod shells with ecological interpretation of species assemblages. The latter is based on mutual climatic range analysis, complemented by probability density function-based climatic niche modelling using modern species distribution data as reference. The composition of gastropod assemblages showed distinct variations across the sequences, indicating shifts in ecosystem characteristics and associated climatic conditions. We identified a significant relationship between specific ecological groups of gastropods and δ¹⁸O_shell values. Predominantly xerophilous assemblages linked to stadial phases showed more negative δ¹⁸O_shell signals, whereas mesophilous assemblages linked to interstadial and interglacial phases corresponded to more positive values. δ¹⁸O_shell signals reflect the isotopic composition of ingested precipitation, which in the studied region is closely linked to temperature. Transfer function-based reconstructions indicate a mean growing season temperature difference of ~4.9°C between stadial and interglacial phases. Furthermore, predictor analyses and climatic range modelling suggest, that species compositions strongly correspond to mean annual precipitation amounts. Reconstructed mean annual precipitation estimates range from ~510 mm during glacial phases to ~770 mm during interglacials. These results provide new proxy-based quantitative climate data for stadial and interglacial conditions in the Caucasus region and demonstrate the potential of gastropod shell assemblages as robust proxies for palaeoclimate reconstruction.