Abstract
AbstractThe Miocene period saw substantially warmer Earth surface temperatures than today, particularly during a period of global warming called the Mid Miocene Climatic Optimum (MMCO; ∼17–15 Ma). However, the long‐term drivers of Miocene climate remain poorly understood. By using a new continuous climate‐biogeochemical model (SCION), we can investigate the interaction between volcanism, climate and biogeochemical cycles through the Miocene. We identify high tectonic CO2 degassing rates and further emissions associated with the emplacement of the Columbia River Basalt Group as the primary driver of the background warmth and the MMCO respectively. We also find that enhanced weathering of the basaltic terrane and input of explosive volcanic ash to the oceans are not sufficient to drive the immediate cooling following the MMCO and suggest that another mechanism, perhaps the change in ocean chemistry due to massive evaporite deposition, was responsible.
Highlights
Miocene climate was generally warm, and the Mid Miocene Climatic Optimum (MMCO; ∼17–15 Ma) was associated with a global average surface temperature around 5°C warmer than the pre-industrial (Burls et al, 2021; Goldner et al, 2014; Zachos et al, 2008)
A warmer Miocene world is likely the result of higher rates of CO2 input from arcs and rifts (Brune et al, 2017; Domeier & Torsvik, 2019; Merdith et al, 2019), combined with a less ‘weatherable’ continental surface (Caves Rugenstein et al, 2019; Raymo & Ruddiman, 1992), while the MMCO onset has been linked to the emplacement of the Columbia River Basalt Group (CRBG) in the northwestern United States (Barry et al, 2013; Reidel, 2015)
Returning to the SCION predictions, a clear mismatch between the baseline output and proxy data is visible during the MMCO (∼17–14 Ma) and the following Mid-Miocene Climate Transition (MMCT) (13.9 –12 Ma) where the model does not capture temperature, CO2 and the carbon isotope composition change associated with climatic variability (Figure 2)
Summary
Miocene climate was generally warm, and the Mid Miocene Climatic Optimum (MMCO; ∼17–15 Ma) was associated with a global average surface temperature around 5°C warmer than the pre-industrial (Burls et al, 2021; Goldner et al, 2014; Zachos et al, 2008). This resulted from a stronger greenhouse effect, with atmospheric CO2 levels between 600 and 800 ppm (Rae et al, 2021). Recent research indicates ∼95% of the CRBG was emplaced in a 750 kyr period from 16.7 Ma onwards (Kasbohm & Schoene, 2018), supporting the theory that volcanic greenhouse gas release may have led to the MMCO (Armstrong McKay et al, 2014; Babila & Foster, 2021)
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