Carbonate Systems Change during Icehouse to Greenhouse Transition

许多人担心，人类活动正在把我们星球的生物圈和生态系统推向一种不可能恢复的状态。虽然没有人能预测下一次状态转变何时发生，地球将以多快的速度进入另一种状态，以及在转变之后等待我们的是什么样的世界，但地质记录为这些问题提供了答案，因为地球不止一次经历了全球规模的状态转变。在这些变化中，没有一个比大约2.52亿年前的二叠纪末大灭绝（LPE）更具破坏性，当时超过92%的生物消失了。然而，在LPE之前，地球系统在4200万年的时间间隔内跨越了一系列不可逆转的阈值，导致了碳酸盐沉积物中记录良好的关键转变。在这些转变中，没有一个比发生在大约2.94亿年前的快速和不可逆转的转变更与现代气候变化辩论相关，这一事件与晚古生代冰河时代（LPIA）的主要阶段结束相吻合。这标志着地球系统最后一次从冰库模式过渡到温室模式，许多人认为，由于大气中化石燃料碳的积累以及随之而来的陆地和海洋碳汇的破坏，我们的星球即将经历这种转变。当时，就像现在一样，大气中二氧化碳的快速积累被视为导致全球变暖的原因。二叠纪二氧化碳增加的原因知之甚少，从火山作用增强到硅酸盐风化作用减少的解释已经提出。然而，我们的工作强烈表明，泛古陆西北部碳酸盐工厂的失控破坏在最初减少并最终关闭海洋中的一个主要碳汇方面发挥了重要作用。到了晚二叠世，碳酸盐几乎全部消失，取而代之的是生物硅质的“玻璃斜坡”，其环境不利于碳酸盐沉积物的生成和保存。因此，我们建议研究晚古生代冰窖温室过渡，括号中的LPIA和LPE事件结束时，通过棱镜的碳酸盐系统，然后，因为它是现在，在二叠纪由于大气中的CO2和相关的全球变暖的普遍增加的压力下。因此，研究二叠纪海洋退化与现代气候变化问题高度相关，特别是考虑到二叠纪海洋的组成与现代海洋的组成相似。这项研究将揭示现代环境辩论，并可能提供洞察力，如果我们继续推动地球系统超越临界阈值，人类将面临什么。在研究上一次从冰库到温室的转变是如何展开的，即大约2.94亿至2.52亿年前，我们的研究将有助于通过过去的事物的棱镜更好地理解未来的事物。

Many fear that human activities are pushing our planet's biosphere and ecosystems towards an alternate state from which it will be impossible to go back. While no one can predict when the next state shift will occur, how fast the planet will tip into an alternate state, and what kind of world awaits us beyond the shift, the geological record provides answers to these questions as the Earth has more than once undergone state shifts of global magnitude. Of these shifts, none were more devastating than the Latest Permian Extinction (LPE) some 252 million years ago when more than 92% of living creatures vanished. Before the LPE however, the Earth System crossed a series of irreversible thresholds over a 42-million year interval resulting in critical transitions that are well recorded in carbonate sediments. Among these transitions, none is more relevant to the modern climate change debate than the rapid and irreversible shift that occurred some 294 million year ago, an event that coincides with the end of the main phase of the Late Paleozoic Ice Age (LPIA). This marks the last time the Earth Systems transitioned from an icehouse mode to a greenhouse mode, a transition many believe our planet is about to experience due to the accumulation of fossil fuel carbon in the atmosphere and the concomitant destruction of carbon sinks on land and in the oceans. Then, just as now, it was the rapid buildup of CO2 in the atmosphere that is seen as having caused global warming. The cause for the Permian CO2 increase is poorly understood, and explanations ranging from enhanced volcanism to reduced silicate weathering have been proposed. Our work, however, strongly suggests that the runaway destruction of carbonate factories all along northwestern Pangea played a major role in first reducing, and eventually shutting down, a major carbon sink in the ocean. By the Late Permian, carbonates were all but eradicated and were replaced by biosiliceous "glass ramps" in an environment inimical to the production and preservation of carbonate sediments. We thus propose to study the Late Paleozoic icehouse to greenhouse transition, bracketed by the end of the LPIA and the LPE event, through the prism of the carbonate system which was then, as it is now, under increasing stress during the Permian due to a general increase in atmospheric CO2 and associated global warming. Looking into the Permian oceanic deterioration is thus highly relevant to the modern climate change issue, especially considering that the composition of the Permian oceans was similar to that of modern oceans. This research will shed light into the modern environmental debate and may provide insights into what is in store for humans if we keep pushing the Earth System beyond critical thresholds. In examining how the last icehouse-to-greenhouse shift unfolded, i.e. some 294-252 million years ago, our research will contribute to a better understanding of things to come, through the prism of things that were.