Did climate changes trigger the Late Devonian Kellwasser Crisis? Evidence from a high-resolution conodont δ18OPO4 record from South China

The impact of climate change on biodiversity has been the focus of studies on the Phanerozoic biotic crises. However, it is still controversial whether climate change has caused the Frasnian-Famennian (F-F) biotic crisis since there is no unequivocal view on the global climate change during this critical period. In order to reconstruct palaeotemperatures during the F-F transition in South China (eastern Palaeotethys), a high-resolution oxygen isotope (δ18OPO4) record was obtained based on 104 measurements of conodont apatite from the Yangdi section. The oxygen isotope record based on mono-generic samples reveals an increase in δ18OPO4 by 0.7‰ in the Lower Kellwasser horizon (LKH) and 1.4‰ in the Upper Kellwasser horizon (UKH), translating into low-latitude surface water cooling of ∼3 °C and ∼6 °C, respectively. These two δ18OPO4 shifts agree well with the time-equivalent δ18OPO4 records from the western Palaeotethys, suggesting that two climate cooling pulses in conjunction with the deposition of the Kellwasser horizons are a global signal during the F-F transition. The positive shift of δ18OPO4 coincides with positive excursion in carbon isotope of carbonates (δ13Ccarb) in the UKH, indicating that enhanced burial of organic carbon resulted in a drop in atmospheric pCO2 and thus global climate cooling. Cooling started immediately before the Upper Kellwasser biotic crisis, with the lowest temperature documented at the top of the UKH. Climate cooling during the deposition of the LKH is observed in conjunction with the sharp decline in metazoan reefs. The coincidence of cooling and the Kellwasser biotic crisis suggests that global cooling played a major role in the collapse of ecosystems.