Global cooling initiated the Middle-Late Mississippian biodiversity crisis

During the Mississippian period, metazoan reefs and other marine faunas gradually recovered from the Late Devonian mass extinctions and reached a peak in the late Visean (~334–332 Ma). Faunal diversity started to decline from the latest Visean (~332–330 Ma) through Serpukhovian (~330–323 Ma), with significant genera/species losses and ecosystem reconstruction. This Middle-Late Mississippian biodiversity crisis (M-LMBC) was thought to have been caused by global cooling associated with the late Paleozoic Ice Age (LPIA), but existing sedimentological and temperature proxy data suggest that the global cooling event—that marks the onset of the main glaciation phase of LPIA—happened either ~4 Myr before or ~ 1–5 Myr after the initial biodiversity decline at ~332 Ma. Here, we report oxygen isotope data of diagenetically screened, well-preserved brachiopod calcite (δ¹⁸O_calcite) from late Visean-Serpukhovian (or Middle-Late Mississippian; ~334–323 Ma) strata in South China where biodiversity data are well documented. The δ¹⁸O_calcite data reveal a ~ 2.0‰ positive shift from −4.6 ± 0.2‰ to −2.7 ± 0.5‰ with an estimated ~4.7–5.5 °C drop in sea surface temperature (SST) during ~332.5–331.5 Ma in the late Visean. This cooling event coincides with fast decline of metazoan reef abundance, followed by decrease of benthic faunal diversity. The δ¹⁸O_calcite data, in combination with calibrated sedimentological and biodiversity data, demonstrate the coupling between late Visean (~332 Ma) onset of the main glaciation phase of the LPIA and initiation of the M-LMBC.