Middle Miocene Climate Transition
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| Middle Miocene Climate Transition | |
|---|---|
| Name | Middle Miocene Climate Transition |
| Period | Miocene |
| Epoch | Neogene |
| Time start | ~14.9 Ma |
| Time end | ~14.0 Ma |
| Significance | major global cooling and Antarctic ice expansion |
Middle Miocene Climate Transition The Middle Miocene Climate Transition was a major Cenozoic cooling event marked by global temperature decline, Antarctic ice-sheet expansion, and shifts in ocean circulation during the Neogene. It intersected with tectonic reorganizations, volcanic episodes, and biotic turnovers that affected terrestrial and marine faunas across multiple continents. Studies of the interval draw on stratigraphic records, isotope geochemistry, and climate modeling to reconstruct drivers and consequences for Earth System components.
Background and chronological framework
The temporal placement of the event is constrained by integrated stratigraphy from the International Commission on Stratigraphy, magnetostratigraphy tied to the Geomagnetic Polarity Time Scale, and radiometric ages from volcanic units associated with the Eocene–Oligocene and Pliocene chronologies. Biostratigraphic markers such as planktonic foraminifera lineages recorded in sites from the Ocean Drilling Program and Integrated Ocean Drilling Program permit correlation with terrestrial mammal faunas described in the European Neogene and North American Land Mammal Ages. Key boundaries are referenced against the Langhian and Serravallian stage definitions ratified by the International Commission on Stratigraphy.
Causes and mechanisms
Proposed drivers include changes in atmospheric CO2 reconstructed from proxies associated with the Maastrichtian–Neogene carbon cycle, tectonic uplift of regions like the Tibetan Plateau and the Andes, and gateway reorganizations such as restriction of the Tethys Sea and shoaling of the Central American Seaway. Episodic volcanism in provinces like the Kerguelen Plateau and Carpathian basins may have influenced aerosol forcing and weathering fluxes to the Amazon Basin and Sahara. Orbital forcing associated with eccentricity, obliquity, and precession cycles tied to the Milankovitch theory modulated insolation patterns recorded in marine and terrestrial archives curated by institutions such as the Smithsonian Institution and the Natural History Museum, London.
Global climate and oceanographic changes
Sea-surface cooling and thermohaline adjustments are evident in records from the North Atlantic Ocean, South Pacific Ocean, and Indian Ocean, with concomitant changes to the Antarctic Circumpolar Current and deep-water formation in regions analogous to the modern North Atlantic Deep Water and Antarctic Bottom Water. The expansion of Antarctic ice influenced sea level documented in sequences from the Mediterranean Sea, Caribbean Sea, and Baltic Sea. Paleotemperature reconstructions compiled by the Paleocene-Eocene Thermal Maximum research community and datasets hosted at the National Oceanic and Atmospheric Administration inform interpretations of cooling magnitude and pacing.
Biotic responses and ecosystem impacts
Faunal turnovers are recorded in marine clades such as planktonic foraminifera, diatoms, and radiolarians described in the literature from the Scripps Institution of Oceanography and University of California, Berkeley collections, and in terrestrial mammal assemblages from the Siwalik Hills, Oligocene–Miocene basins of Central Europe, and the Great Plains. Vegetation shifts from subtropical to more temperate assemblages are inferred from palynological studies in cores held by the British Geological Survey and the Geological Survey of Japan, with observable effects on herbivore evolution documented in museum collections at the American Museum of Natural History. Coral reef decline and reef restructuring are reported from occurrences in the Red Sea and Mediterranean Basin.
Geochemical and proxy evidence
Isotopic excursions in benthic and planktonic foraminifera oxygen isotopes measured in cores from the Deep Sea Drilling Project and Ocean Drilling Program provide primary evidence for cooling and ice growth. Carbon isotope shifts in organic matter and carbonate, alongside trace-metal proxies such as Mg/Ca and Sr/Ca, were analyzed in laboratories affiliated with the Max Planck Society and the Woods Hole Oceanographic Institution. Boron isotope pH reconstructions and stomatal proxies from collections at the Royal Botanic Gardens, Kew contribute to CO2 estimates, while neodymium isotopes and detrital provenance studies implicate erosional changes tied to uplift in the Himalaya and Andean orogens.
Regional expressions and case studies
Regional syntheses include Mediterranean salinity and sapropel records studied by teams from the Università di Bologna and Université Aix-Marseille, Indian Ocean records influenced by monsoon dynamics evaluated by researchers at the Indian Institute of Science, and Southern Ocean sections cored by expeditions involving the Australian Antarctic Division. North Pacific records tied to the Bering Strait gateway, Caribbean reef studies involving the Smithsonian Tropical Research Institute, and terrestrial sequences from the Siwalik Group offer contrasting local manifestations of the global signal.
Modeling and implications for climate sensitivity
Coupled atmosphere–ocean general circulation models developed at centers such as the National Center for Atmospheric Research, Met Office Hadley Centre, and the Lawrence Livermore National Laboratory have been used to test hypotheses about CO2, ice-sheet albedo feedbacks, and tectonic boundary conditions. Model–proxy comparisons inform estimates of equilibrium climate sensitivity and transient climate response relevant to debates in reports by the Intergovernmental Panel on Climate Change and paleoclimate syntheses published by societies like the American Geophysical Union and European Geosciences Union.