Oceanic stable isotope composition and a scenario for the Permo‐Triassic crisis

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Abstract
Stable carbon isotope data from brachiopod shells from the Upper Permian Kapp Starostin Formation (West Spitsbergen) indicate that the oceanic carbon isotopic ratio, which had already been very high in the late Permian, rapidly increased by almost 4 per mil and then dramatically declined by more than 10 per mil in the very latest Permian. This pattern is essentially repeated by the oxygen isotope curve. These data show that a geologically rapid switch between two fundamentally different states of the Earth's exosystem occurred near the Permo‐Triassic transition. The late Permian state of the global system was profoundly different from the modern one in that vast amounts of organic carbon were stored, presumably in the form of easy‐to‐mobilize sapropel‐like deposits, below the oceanic redoxcline. Under such conditions—which we propose to call overfed ocean—nutrients were intensely recycled to seawater, thus allowing the ocean to sustain a huge standing crop of the biosphere. Deposition of large amounts of organic carbon in the ocean liberated corresponding amounts of oxygen, thus leading to high oxygen levels in the atmosphere. In the latest Permian, the organic matter decaying in the ocean was subject to rapid oxidation due to appearance of the modern type of ocean which is characterized by vigorous bottom circulation and net heterotrophy. The appearance of these conditions—which we propose to call hungry ocean—led to removal of nutrients from seawater and to a substantial drop in atmospheric oxygen contents. The resulting nutrient deficiency in the ocean, oxygen depletion in the atmosphere, and other effects of this paleoceanographic change must have caused major extinctions.