Societal responses to cold-season rainfall variability: a speleothem perspective on Byzantine and Hittite climate interactions in Late Holocene Türkiye and southeast Europe

Understanding past hydroclimate dynamics of the Eastern Mediterranean is crucial for predicting future climate impacts. However, the ‘Marmara Transition Zone’ in northwest Türkiye, a region of significant societal transformation, lacks high-resolution pre-industrial climate records. Continuous paleoclimate reconstructions are critical to reveal the nature and pattern of Late Holocene hydroclimatic changes and extremes, and to study their impacts on societies. Here, we present a precisely dated and sub-decadal resolution speleothem record from Uzuntarla cave, located near to Istanbul (historically Byzantium and Constantinople), that shows sensitivity to cold-season rainfall amount and seasonality for the Late Holocene. Prior to 2005 CE, stalagmite U-1 reveals two periods of high multidecadal variability of cold-seasonal rainfall in ∼1900-400 BCE and ∼690–1900 CE, separated by a relatively stable phase. This variability aligns with the rise and fall of Byzantine agrarian productivity between ∼350 and 1250 CE, while the most pronounced aridification anomaly in ∼1210-1170 BCE coincides with the collapse of the Hittite Empire (c. ∼1200 BCE), partly linked to regional famine and drought. Our findings indicate that the transition from the Late Bronze Age to the Iron Age in the Marmara Transition Zone was marked by a pronounced shift in the regional climate regime. Namely, that a previously warmer and more stable 'Mediterranean-style' climate shifted toward cooler conditions characterised by increased rainfall variability, and a greater influence of moisture sourced from the Black Sea. Therefore, we suggest that cold-seasonal rains played a critical role in shaping human-climate interactions, power dynamics, and social stability in the Eastern Mediterranean during the Late Holocene. This record offers valuable context for understanding how hydroclimate variability influenced past societies, highlighting the importance of climate as a driver in historical societal resilience and collapse. • Detailed is a new paleoclimate record for northwest Türkiye near Istanbul. • Stalagmite U-1 is sensitive to shifts in moisture source, amount and seasonality. • Moisture availability tracks key Byzantine socioeconomic shifts (∼350–1250 CE). • The largest aridity signal coincides with the Hittite Empire's collapse (∼1200 BCE). • Explored is climates role as an influence towards societal resilience or collapse.