![]() The oceanic absorption of anthropogenic CO 2 has disturbed naturally formed vertical gradients of the δ 13C of DIC (δ 13C-DIC) where δ 13C is defined as with the Vienna Pee Dee Belemnite standard. We conclude that the Paleocene-Eocene Thermal Maximum is a geologic analogue of future global carbon cycle perturbations under continued rapid anthropogenic carbon emissions.Īnthropogenic carbon (C) emissions have led to an accumulation of 13C-depleted carbon in the atmosphere and the upper ocean, diluting the isotopic composition of carbon dioxide (CO 2) and dissolved inorganic carbon (DIC) (referred to as the 13C Suess effect) 1, 2. Our findings suggest an elimination or reversal of the natural vertical gradient in the δ 13C of dissolved inorganic carbon by 2100 unless anthropogenic carbon emissions are reduced soon. This reduction is driven by oceanic absorption of anthropogenic carbon dioxide, which is depleted in carbon-13. We project a decrease in the globally averaged δ 13C of dissolved inorganic carbon in the surface ocean of between −1.8 to −6.3 ‰ by 2100. Here we present simulations from an observationally constrained ocean model under various greenhouse gas emissions scenarios. Paleoceanographic records suggest that the present-day vertical gradient in the stable carbon isotopic composition (δ 13C) of dissolved inorganic carbon in the ocean was reversed during the Paleocene-Eocene Thermal Maximum, an early period of relatively rapid release of carbon into the climate system.
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