A 12.7–5.7 ka multi-proxy stalagmite record from Cueva Fantasma (Atapuerca, N Spain): inland Iberian hydroclimate variability with combustion-derived laminae during the 8.2 ka interval.

We present a multi-proxy record of a speleothem from Cueva Fantasma (Atapuerca, N Spain) spanning 12.7–5.7 ka that documents inland Iberian hydroclimate variability and a local expression of the 8.2 ka event.  U–Th chronology indicates continuous deposition with accelerated accretion (higher drip rates) between ~8.5 and 7.7 ka. From base to top, three morphological stratigraphic parts were defined: (i) transparent columnar calcite with low detrital input; (ii) a laminated interval of black, organic-rich calcite laminae with high detrital input; and (iii) an upper part reflecting post 8.2 ka event stabilization characterized by moderate growth, marked absence of black laminae, and lower detrital imprint. Fluorescence and oil-immersion petrography highlight that black carbon occurs as films and clustered particulates that follow the growth-lamina geometry, with films preferentially recorded or preserved along micro-columns. SEM–EDX identifies combustion-derived particulates comprising soot-like carbon films and ash-rich detritus within the calcite crystals and/or detritus matrix. Trace-element profiles exhibit co-enrichment especially in Mn and Th across 8.5–7.7 ka, consistent with enhanced soil flushing and drip-system reorganization. High-resolution δ¹⁸O and δ¹³C data indicate wetter, vegetation-active conditions prior to ~8.5 ka, a hydrological pulse during ~8.5–7.7 ka expressed by increased variability and δ¹³C–δ¹⁸O co-variability, and moderation thereafter. Thus, the 8.2 ka interval is captured not by a hiatus but by a facies and geochemical shift under wetter, more seasonal/flashy recharge, characterized by black laminae containing soot-like films and ash-rich detritus, Mn–Th peaks, and slightly accelerated growth. The combustion-derived particulates, soot-like films and ash-rich micrite/detritus, occur as closely spaced clusters which supports multiple discrete in-cave fire episodes. This interpretation is distinct from external wildfire fallout and is based on the tight lamina-scale coupling, and coeval hydrological proxies. This record provides the first speleothem evidence from Atapuerca of the 8.2 ka climatic anomaly embedded within regional Holocene hydroclimate variability, alongside independent evidence for repeated in-cave combustion during that interval.