Abstract
Abstract. The Middle Eocene Climatic Optimum (MECO), a ∼500 kyr episode of global warming that initiated at ∼ 40.5 Ma, is postulated to be driven by a net increase in volcanic carbon input, but a direct source has not been identified. Here we show, based on new and previously published radiometric ages of volcanic rocks, that the interval spanning the MECO corresponds to a massive increase in continental arc volcanism in Iran and Azerbaijan. Ages of Eocene igneous rocks in all volcanic provinces of Iran cluster around 40 Ma, very close to the peak warming phase of the MECO. Based on the spatial extent and volume of the volcanic rocks as well as the carbonaceous lithology in which they are emplaced, we estimate the total amount of CO2 that could have been released at this time corresponds to between 1052 and 12 565 Pg carbon. This is compatible with the estimated carbon release during the MECO. Although the uncertainty in both individual ages, and the spread in the compilation of ages, is larger than the duration of the MECO, a flare-up in Neotethys subduction zone volcanism represents a plausible excess carbon source responsible for MECO warming.
Highlights
The Middle Eocene Climatic Optimum (MECO) is characterized by surface and deep ocean warming, both of approximately 2–6 ◦C
The MECO inherently differs from the early Paleogene transient warming events such as the Paleocene– Eocene Thermal Maximum (PETM; ∼ 56 Ma) primarily in its longer duration (∼ 500 kyr) of warming, precluding a sudden trigger but rather suggesting a continued driver (Bohaty and Zachos, 2003; Sluijs et al, 2013)
To quantitatively assess whether volcanism in the Iran– Azerbaijan region could have been a contributor to global warming during the MECO, we present a compilation of new and previously published radiometric ages for volcanic rocks and estimate eruptive volumes of the flare-up in Iran to evaluate how much CO2 could have been released during this continental arc flare-up
Summary
The Middle Eocene Climatic Optimum (MECO) is characterized by surface and deep ocean warming, both of approximately 2–6 ◦C. Reconstructions and simulations of the carbon cycle point to an imbalance in the longterm inorganic carbon cycle during the MECO (Sluijs et al, 2013), caused by enhanced volcanism and sustained by diminished continental silicate weathering (van der Ploeg et al, 2018) This scenario is quantitatively far from settled, partly because recent analyses based on foraminifer boron isotope ratios suggest that atmospheric CO2 concentrations rose by significantly less than a doubling and did not rise substantially during the onset of the MECO (Henehan et al, 2020). To quantitatively assess whether volcanism in the Iran– Azerbaijan region could have been a contributor to global warming during the MECO, we present a compilation of new and previously published radiometric ages for volcanic rocks and estimate eruptive volumes of the flare-up in Iran to evaluate how much CO2 could have been released during this continental arc flare-up
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