Zinc isotope perspective on global carbon cycling during the onset of the late Paleozoic icehouse
Yutian Zhong, Jitao Chen, Sheng‐Ao Liu, Chengshuai Yuan, Biao Gao, Terry T. Isson, Thomas J. Algeo, Qingyi Sheng, Bo Chen, Genming Luo, Xiangdong Wang, Wenkun Qie
Abstract
Abstract The onset of the late Paleozoic icehouse coincided with a large global carbon-cycle perturbation (represented by the mid-Tournaisian carbon isotope excursion [TICE]), although the underlying cause of this isotopic event remains uncertain. Zinc (Zn), an essential micronutrient for plankton, has an isotopic composition (δ66Zn) in seawater that is sensitive to subtle fluctuations in marine carbon (C) cycling. Here, we investigated C cycling during the TICE using paired carbonate δ66Zn-δ13C and organic δ13C records from two widely spaced sections in South China. These records reveal coupling between δ66Zn and δ13C over an ~4 m.y. interval in the form of two positive excursions (Peaks I and II) separated by a negative shift (interpeak). Peak I is attributed to enhanced marine primary productivity (MPP), which was stimulated by increased micronutrient supply linked to enhanced silicate weathering and/or upwelling. The interpeak may record oxidation of remobilized organic matter from continental shelves exposed by glacio-eustatic sea-level fall, which, in turn, promoted MPP again and resulted in Peak II. Thus, the TICE records complex climate–carbon cycle feedbacks that may have led to large-scale organic carbon burial and driven stepwise cooling, marking the onset of a sustained late Paleozoic icehouse climate.