Reversed deep-sea carbonate ion basin gradient during Paleocene-Eocene thermal maximum

The Paleocene-Eocene thermal maximum (PETM, similar to 55 Ma ago) was marked by widespread CaCO3 dissolution in deep-sea sediments, a process that has been attributed to massive release of carbon into the ocean-atmosphere system. The pattern of carbonate dissolution is key to reconstructing changes in deep sea carbonate chemistry and, ultimately, the rate, magnitude, and location of carbon input. Here we show that during the PETM, the deep-sea undersaturation was not homogeneous among the different ocean basins. Application of a sediment model to a suite of data records from different sites and ocean basins shows that a globally uniform decrease in deep-sea carbonate ion concentration ([CO32-]) is inconsistent with the data. Rather, we demonstrate that deep-sea [CO32-] increased from the Atlantic through the Southern Ocean into the Pacific. Our results show that the PETM deep-sea [CO32-] basin gradient during dissolution was reversed relative to the modern.