Carbonate Systems Change during Icehouse to Greenhouse Transition

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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.