Carbonate Systems Change during Icehouse to Greenhouse Transition

许多人担心，人类活动正在将我们星球的生物圈和生态系统推向一种无法回头的替代状态。虽然没有人能预测下一次状态变化将在何时发生，地球将以多快的速度进入另一种状态，以及在变化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范围的状态变化。在这些变化中，没有一次比2.52亿年前最近的二叠纪灭绝(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，导致了关键的转变，这在碳酸盐沉积物中得到了很好的记录。在这些转变中，与现代气候变化争论最相关的是大约2.94亿年前发生的快速且不可逆转的转变，这一事件恰逢晚古生代冰期(LPIA)主要阶段的结束。这标志着地球系统最后一次从冰库模式转变为温室模式，许多人认为，由于化石燃料碳在大气中的积累，以及随之而来的陆地和海洋碳汇的破坏，地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认为是导致全球变暖的原因。二叠纪二氧化碳增加的原因人们知之甚少，人们提出了从火山作用增强到硅酸盐风化减弱的各种解释。然而，我们的研究有力地表明，盘古大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，碳酸盐几乎全部被消灭，取而代之的是生物硅质的“玻璃坡道”，其环境不利于碳酸盐沉积物的生产和保存。因此，我们建议通过碳酸盐体系的棱镜来研究晚古生代冰库到温室的转变，以LPIA和LPE事件的结束为界，当时和现在的碳酸盐体系在二叠纪由于大气二氧化碳的普遍增加和相关的全球变暖而承受着越来越大的压力。因此，研究二叠纪海洋的恶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，并可能为人类提供洞察力，如果我们继续推动地球系统超过关键门槛的话。在考察上一次从冰屋到温室的转变是如何展开的，即大约2.94亿-2.52亿年前，我们的研究将有助于通过过去的事物的棱镜更好地理解即将到来的事物。

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.