Mercury isotope evidence for recurrent photic-zone euxinia triggered by enhanced terrestrial nutrient inputs during the Late Devonian mass extinction
Mercury isotope evidence for recurrent photic-zone euxinia triggered by enhanced terrestrial nutrient inputs during the Late Devonian mass extinction
复制标题
DOI：
10.1016/j.epsl.2023.118175
复制
发表时间：
2023-07
影响因子：
5.3
通讯作者：
Wang Zheng;G. Gilleaudeau;T. Algeo;Yaqiu Zhao;Yi Song;Yuanming Zhang;S. Sahoo;A. Anbar;S. Carmichael;S. Xie;Cong-Qiang Liu;Jiubin Chen
中科院分区：
文献类型：
--
作者：
Wang Zheng;G. Gilleaudeau;T. Algeo;Yaqiu Zhao;Yi Song;Yuanming Zhang;S. Sahoo;A. Anbar;S. Carmichael;S. Xie;Cong-Qiang Liu;Jiubin Chen
在晚泥盆世期间，以富含有机物的黑色页岩的全球广泛沉积为标志的广泛的海洋缺氧是弗拉斯阶-法门阶（FFB，13.72亿年前）和泥盆纪-石炭纪边界（DCB，13.59亿年前）的大规模缺氧的主要因素，尽管这些脱氧事件的触发因素仍在争论中。在这里，我们采用一种新的古氧化还原代理，汞同位素，研究晚泥盆世海洋氧化还原变化及其原因。我们没有发现在北美的汞富集无论是FFB或DCB，从而反对全球规模的火山活动作为晚泥盆世环境和生物危机的触发器的假设。FFB和DCB之间的质量无关分馏（Δ 199 Hg）和质量相关分馏（δ 202 Hg）均发生逐渐负移，表明与陆地有机质相关的汞输入逐渐增加。此外，Δ 199 Hg（降至-0.19 ‰）沿着δ 202 Hg同时发生的多次突然负偏移正好发生在FFB上方和DCB上，这为在北美陆表海陆地输入增加之前经常出现的透光带真彩（PZE）提供了强有力的证据。我们认为，陆地输入的营养物质的增加，可能是通过扩张的维管陆地植物，刺激海洋初级生产力，并最终PZE，这可能是一个关键的杀死机制晚泥盆世大规模灭绝。
Widespread oceanic anoxia marked by globally extensive deposition of organic-rich black shale during the Late Devonian was a major factor in the mass extinctions at the Frasnian-Famennian (FFB,∼ 372 million years ago) and Devonian-Carboniferous boundaries (DCB,∼ 359 million years ago), although the triggers for these deoxygenation events are still under debate. Here, we apply a novel paleoredox proxy, Hg isotopes, to investigate Late Devonian ocean redox variation and its causes. We found no Hg enrichments in North America across either the FFB or DCB, thus arguing against the hypothesis of global-scale volcanism as the trigger for Late Devonian environmental and biotic crises. Gradual negative shifts of both mass-independent fractionation (Δ 199 Hg) and mass-dependent fractionation (δ 202 Hg) occurred between the FFB and DCB, suggesting a progressive increase of Hg inputs associated with terrestrial organic matter. Moreover, multiple abrupt negative excursions of Δ 199 Hg (down to− 0.19‰) along with concurrent positive shifts of δ 202 Hg occurred just above the FFB and across the DCB, providing strong evidence for recurrent photic-zone euxinia (PZE) that was preceded by increasing terrestrial inputs in the epicontinental seas of North America. We suggest that the increase of terrestrial inputs of nutrients, probably via expansion of vascular land plants, stimulated marine primary productivity and eventually PZE, which may have been a key kill mechanism for the Late Devonian mass extinction.