A seasonally resolved late Holocene paleoclimate record from Sofular Cave, Northern Türkiye.

Understanding how climate change manifests across the Mediterranean basin is critical for predicting the impacts of future climate change. The Black Sea region (BSR) is one of the most vulnerable areas of the Mediterranean climate change hotspot, owing to its high sensitivity to both local and global-scale climate feedbacks¹. However, few paleoclimate records exist with sufficient resolution, and length, to fully assess significance of these feedbacks on timescales exceeding the window of instrumental observation². Here, we present a ~230-year-long, seasonally-resolved stable isotope record record of effective moisture and temperature variability from stalagmite So-11, which grew in Sofular Cave (Northern Türkiye) between 1779 and 2008 CE. The sample contains 229 continuous, well-developed laminae couplets with a mean wavelength of ~0.95 mm a^-1, suggesting that each dark-to-light couplet corresponds to one calendar year. This assumption is supported by two U-Th ages, which show good agreement with the layer-counted chronology generated using the date of collection (2008 CE) as an upper anchor point. Minima in δ¹³C closely track the dense, dark, compact calcite layers, and are typically followed by a distinct δ¹³C peak in conjunction with formation of white, porous calcite layers. We interpret these oscillations as seasonal changes in effective moisture, with the lowest δ¹³C values corresponding to high drip rates, lower CO₂ degassing, and weaker fractionation during winter months – reflecting the high responsivity of the Sofular Cave system to transient changes in local precipitation^3,4. Marked changes in the geochemistry of So-11 also coincide with the Little Ice Age (1850 to 1870 CE), and the progressive increase in global atmospheric CO₂ in response to increased fossil fuel combustion during the 20th and 21st centuries⁵. Our results underscore how high-resolution, speleothem-based paleoclimate reconstructions can provide important context not only for constraint of global circulation model (GCM) simulations, but also closer examination of human-climate-environment interactions during the Late Holocene. 

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¹Giorgi, F. (2006) Geophysical Research Letters 33(8):  L08707
²Burstyn, Y. et al. (2019) Quaternary 2:16
³Göktürk et al. (2011) Quaternary Science Reviews 30: 2433-2445
⁴Rudzka, D. et al. (2011) Geochimica et. Cosmochimica Acta 75 : 4321–4339
⁵Bauska, T. K. et al. (2015) Nature Geoscience 8: 383–387