Abstract
The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at about 40 Ma. In comparison to the most known global warming events of the Paleogene, the MECO has some peculiar features that make its interpretation controversial. The main peculiarities of the MECO are a duration of ~500 kyr and a carbon isotope signature that varies from site to site. Here we present new carbon and oxygen stable isotopes records (δ13C and δ18O) from three foraminiferal genera dwelling at different depths throughout the water column and the sea bottom during the middle Eocene, from eastern Turkey. We document that the MECO is related to major oceanographic and climatic changes in the Neo-Tethys and also in other oceanic basins. The carbon isotope signature of the MECO is difficult to interpret because it is highly variable from site to site. We hypothesize that such δ13C signature indicates highly unstable oceanographic and carbon cycle conditions, which may have been forced by the coincidence between a 400 kyr and a 2.4 Myr orbital eccentricity minimum. Such forcing has been also suggested for the Cretaceous Oceanic Anoxic Events, which resemble the MECO event more than the Cenozoic hyperthermals.
Highlights
The Middle Eocene Climatic Optimum (MECO) is a global warming event, which occurred at about 40 Ma and lasted ~500 kyr
The Baskil section displays values that are, on average, 1.0‰ to 1.5‰ lower for δ13C and 2.0‰ to 4.0‰ lower for δ18O, and the amplitude of the fluctuations is generally larger in the Baskil section than in the other records (Fig. 4)
The upper water column counterparts is much larger in the Baskil section
Summary
The Middle Eocene Climatic Optimum (MECO) is a global warming event, which occurred at about 40 Ma and lasted ~500 kyr. Transient climate warming events are commonly explained by the rapid intensification of the greenhouse effect This is supported by a prominent negative carbon isotope (δ13C) peak occurring at the onset of these events in response of massive dissociation of gas hydrates or extensive volcanic events that injected large amounts of light carbon into the ocean-atmosphere system[5,6,7,8]. Over hundreds of thousand years, such as the duration of the MECO, high atmospheric pCO2 increases the weathering of surface rocks, which draws pCO2 from the atmosphere and increases the seawater alkalinity This means that at the time scale of the MECO, a massive injection of greenhouse gases into the atmosphere and the ocean is counterbalanced by carbon cycle feedbacks and would produce an increase in deep-water carbonate deposition, instead of a decrease[9,10]. All evidence indicates that the MECO was different from the Cenozoic hyperthermals, but had several features in common with the Oceanic Anoxic Events of the Cretaceous
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