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Carbon and sulfur cycling during the mid-Ludfordian anomaly and the linkage with the late Silurian Lau/Kozlowskii Bioevent
Palaeogeography, Palaeoclimatology, Palaeoecology ( IF 3 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.palaeo.2020.110152
Jiří Frýda , Oliver Lehnert , Barbora Frýdová , Juraj Farkaš , Michal Kubajko

Abstract The Ludfordian (late Silurian) records one of the largest perturbations in the Phanerozoic marine carbon cycling, the mid-Ludfordian positive δ13Ccarb excursion (MLCIEcarb), which occurred in the aftermath of the Lau/Kozlowskii Bioevent (LKB). There are still controversies regarding origin of the MLCIE and its possible causal link(s) with respect to the preceding LKB. Surprisingly, the isotope fractionation of carbon between inorganic and organic carbon pools during the MLCIE was not investigated in detail. To constrain better this parameter of marine C cycle, its linkage to the LKB, and local sulfur cycle, we analysed high-resolution δ13Ccarb, δ13Corg, and δ34Spy records in the Prague Basin (peri-Gondwana) representing one of the most complete records of the MLCIEcarb in the world. Evaluation of these high-resolution δ13Corg and δ13Ccarb records reveals their tight coupling, which in turn indicates the photosynthetic origin of the MLCIEorg via links to primary production and changing rates of organic carbon burial. On the other hand, our data also reveal a short-term decoupling of the δ13Corg and δ13Ccarb records preceding the MLCIE which may have been related to a purported increase in atmospheric pCO2 levels or anoxic event. The peak of the Δ13C anomaly exactly coincides with the LKB and, therefore, for the first time suggests a tight link between the change in marine carbon cycling and the bioevent. Subsequent rapid drop of the Δ13C values (and by inference also atmospheric pCO2) fits well with a rapid cooling and globally documented regression reported for this time interval. Finally, the documented strong coupling of δ13Ccarb and δ34Spy records during the MLCIE points to an intensive microbial sulfate reduction which should increase carbonate alkalinity input, thus contributing to formation of authigenic carbonates and an increase in δ13C values of DIC (and anticipated seawater carbonate saturation). The coupling of δ13Corg and δ34Spy values suggests a global enhancement of organic carbon and pyrite burial likely driven by an expansion of euxinic (anoxic and sulfidic water column) conditions in the oceans. Present study of C and S isotope variations during the MLCIE reveals for the first time a tight link among carbon and sulfur cycling, global cooling, and reorganization of faunal communities and fits well with purported seawater carbonate hypersaturation at the onset and during MLCIE.

中文翻译:

Ludfordian 中期异常期间的碳和硫循环以及与晚志留纪 Lau/Kozlowskii 生物事件的联系

摘要 Ludfordian(晚志留纪)记录了显生宙海洋碳循环中最大的扰动之一,即中 Ludfordian δ13Ccarb 正偏移(MLCIEcarb),它发生在 Lau/Kozlowskii 生物事件(LKB)之后。关于 MLCIE 的起源及其与前面的 LKB 可能的因果关系仍然存在争议。令人惊讶的是,没有详细研究 MLCIE 期间无机和有机碳库之间碳的同位素分馏。为了更好地限制海洋碳循环的这个参数、它与 LKB 的联系以及当地的硫循环,我们分析了布拉格盆地(冈瓦纳半岛周边)的高分辨率 δ13Ccarb、δ13Corg 和 δ34Spy 记录,代表了最完整的记录之一。世界上的 MLCIEcarb。对这些高分辨率 δ13Corg 和 δ13Ccarb 记录的评估揭示了它们的紧密耦合,这反过来又通过与初级生产和有机碳埋藏变化率的联系表明了 MLCIEorg 的光合作用起源。另一方面,我们的数据还揭示了 MLCIE 之前 δ13Corg 和 δ13Ccarb 记录的短期脱钩,这可能与大气 pCO2 水平或缺氧事件的据称增加有关。Δ13C 异常的峰值与 LKB 完全一致,因此首次表明海洋碳循环的变化与生物事件之间存在紧密联系。随后 Δ13C 值的快速下降(推断也是大气 pCO2)与该时间间隔报告的快速冷却和全球记录的回归非常吻合。最后,MLCIE 期间 δ13Ccarb 和 δ34Spy 记录的强烈耦合表明微生物硫酸盐的强烈还原,这应该会增加碳酸盐碱度输入,从而有助于形成自生碳酸盐和 DIC δ13C 值的增加(和预期的海水碳酸盐饱和度)。δ13​​Corg 和 δ34Spy 值的耦合表明有机碳和黄铁矿埋藏的全球增强可能是由海洋中的富氧(缺氧和硫化水柱)条件的扩张驱动的。目前对 MLCIE 期间 C 和 S 同位素变化的研究首次揭示了碳和硫循环、全球冷却和动物群落重组之间的紧密联系,并且与 MLCIE 开始和期间所声称的海水碳酸盐超饱和状态非常吻合。
更新日期:2021-02-01
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