The continental Middle Miocene Climatic Transition in Southern Europe as derived from clumped isotope analyses

Reconstructing Cenozoic terrestrial paleoclimate is frequently limited by temporal resolution and suitable quantitative tools to reliably assess changes in temperature and aridity. The dynamics of ocean temperatures¹ and chemistry², varying pCO₂³, and faunal assemblages are known to a certain extent, however, terrestrial data on temperatures, which are mostly indirectly derived from fossil assemblages and palynologycal data⁴ are rare. This study contributes to the understanding of the dynamics and variability of terrestrial temperatures during one of the most extreme Neogene climate changes, the Middle Miocene Climate Transition (MCT). The comparison of pCO₂ forecasts for the coming century and reconstructed Mid-Miocene pCO₂ levels suggest that the Mid-Miocene is an important time interval for ascertaining suitable model projections of the future anthropogenic impact on climate. In order to establish an appropriate understanding and modeling of the natural variability of the European/Mediterranean climate system, quantitative climate information of the European continental Mid-Miocene is mandatory. This would facilitate the identification of main drivers of climate evolution in an area which is exposed to the present climate change and its subsequent natural hazards.

 

This study presents a profound and well-dated terrestrial clumped isotope (Δ₄₇) paleosoil carbonate dataset from Spain that ranges from 13.0 to 15.1 Ma (100 kyr resolution) and hence covers an interval that was previously classified as the MCT. The Δ₄₇ data is supported by stable carbon and oxygen isotope analyses that are in agreement with previously published continental and oceanic records. A distinct decline in apparent Δ₄₇-based temperatures between 13.7 and 14.1 Ma reveals a substantial drop in continental temperatures and indicates changes in seasonality of pedogenic carbonate formation. The major cooling thereby coincides with a change in Milanković periodicities and can be linked to oceanic isotope records⁵. While the transition into the MCT shows a high temperature variability indicating varying environmental conditions, calculated oxygen isotopic values of the soil water point to a rather stable moisture source across the MCT in Southern Europe.

 

1: Super, J. R., Thomas, E., Pagani, M., et al. (2018) North Atlantic temperature and pCO₂ coupling in the early-middle Miocene. Geology, 46(6), 519-522.

2: Pearson, P. N., and Palmer, M. R. (1999) Middle Eocene seawater pH and atmospheric carbon dioxide concentrations. Science, 284(5421), 1824-1826.

3: Pagani, M., Freeman, K. H., and Arthur, M. A. (1999) Late Miocene atmospheric CO₂ concentrations and the expansion of C4 grasses. Science, 285(5429), 876-879.

4: Lewis, A. R., Marchant, D. R., Ashworth, A. C., et al. (2008) Mid-Miocene cooling and the extinction of tundra in continental Antarctica. Proceedings of the National academy of Sciences.

5: Holbourn, A., Kuhnt, W., Clemens, S., et al. (2013) Middle to late Miocene stepwise climate cooling: Evidence from a high resolution deep water isotope curve spanning 8 million years. Paleoceanography, 28(4), 688-699.