Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, Japan.
State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.
Heliyon. 2016 Aug 8;2(8):e00137. doi: 10.1016/j.heliyon.2016.e00137. eCollection 2016 Aug.
The largest mass extinction of biota in the Earth's history occurred during the Permian-Triassic transition and included two extinctions, one each at the latest Permian (first phase) and earliest Triassic (second phase). High seawater temperature in the surface water accompanied by euxinic deep-intermediate water, intrusion of the euxinic water to the surface water, a decrease in pH, and hypercapnia have been proposed as direct causes of the marine crisis. For the first-phase extinction, we here add a causal mechanism beginning from massive soil and rock erosion and leading to algal blooms, release of toxic components, asphyxiation, and oxygen-depleted nearshore bottom water that created environmental stress for nearshore marine animals. For the second-phase extinction, we show that a soil and rock erosion/algal bloom event did not occur, but culmination of anoxia-euxinia in intermediate waters did occur, spanning the second-phase extinction. We investigated sedimentary organic molecules, and the results indicated a peak of a massive soil erosion proxy followed by peaks of marine productivity proxy. Anoxic proxies of surface sediments and water occurred in the shallow nearshore sea at the eastern and western margins of the Paleotethys at the first-phase extinction horizon, but not at the second-phase extinction horizon. Our reconstruction of ocean redox structure at low latitudes indicates that a gradual increase in temperature spanning the two extinctions could have induced a gradual change from a well-mixed oxic to a stratified euxinic ocean beginning immediately prior to the first-phase extinction, followed by culmination of anoxia in nearshore surface waters and of anoxia and euxinia in the shallow-intermediate waters at the second-phase extinction over a period of approximately one million years or more. Enhanced global warming, ocean acidification, and hypercapnia could have caused the second-phase extinction approximately 60 kyr after the first-phase extinction. The causes of the first-phase extinction were not only those environmental stresses but also environmental stresses caused by the soil and rock erosion/algal bloom event.
在地球历史上最大的生物灭绝事件发生在二叠纪-三叠纪过渡期，包括两次灭绝，一次是在最晚的二叠纪（第一阶段），一次是在最早的三叠纪（第二阶段）。海水温度升高，表层水伴有缺氧的中深层水，缺氧水侵入表层水，pH 值下降，以及二氧化碳过饱和被认为是海洋危机的直接原因。对于第一阶段的灭绝，我们在这里添加了一个因果机制，从大规模的土壤和岩石侵蚀开始，导致藻类大量繁殖，释放有毒成分，窒息和缺氧的近岸底层水，为近岸海洋动物创造了环境压力。对于第二阶段的灭绝，我们表明，土壤和岩石侵蚀/藻类大量繁殖事件并未发生，但中间水的缺氧-富营养化确实发生了，贯穿了第二阶段的灭绝。我们研究了沉积有机分子，结果表明大量土壤侵蚀指标达到峰值，随后是海洋生产力指标达到峰值。缺氧指标在浅近海海底的东部和西部边缘的古特提斯洋的第一阶段灭绝层出现，但在第二阶段灭绝层没有出现。我们对低纬度海洋氧化还原结构的重建表明，跨越两次灭绝的温度逐渐升高可能导致从混合良好的含氧海洋逐渐转变为分层的缺氧海洋，这一变化始于第一阶段灭绝之前，随后在第一阶段灭绝之后约一百万年或更长时间内，近岸表层水的缺氧和浅中层水的缺氧和富营养化达到顶峰。增强的全球变暖、海洋酸化和二氧化碳过饱和可能导致第二阶段灭绝大约在第一阶段灭绝后 60 千年前发生。第一阶段灭绝的原因不仅是这些环境压力，还有土壤和岩石侵蚀/藻类大量繁殖事件引起的环境压力。
