Eocene Thermal Maximum

Eocene Thermal Maximum
Name	Eocene Thermal Maximum
Period	Eocene
Epoch	Paleogene
Date	~56 Ma
Significance	short-lived global warming event

Eocene Thermal Maximum The Eocene Thermal Maximum was an abrupt, short-lived global warming event near the Paleocene–Eocene boundary that produced rapid climate change, oceanic perturbations, and major biotic turnover. It influenced climate systems, marine chemistry, and terrestrial ecosystems across regions such as Greenland, Antarctica, Europe, Asia, and North America, and remains central to comparisons with modern anthropogenic warming studied by institutions like the National Aeronautics and Space Administration and the United States Geological Survey.

Introduction

The event occurred at the transition between the Paleocene and the Eocene epochs and is often associated in stratigraphy with the Paleocene–Eocene Thermal Maximum interval recognized in cores from the Atlantic Ocean, Pacific Ocean, and Indian Ocean. Key researchers from universities such as University of California, Berkeley, University of Oxford, and Columbia University have reconstructed its pace and magnitude using proxies developed in programs like the Deep Sea Drilling Project and the Ocean Drilling Program. The phenomenon has been invoked in discussions at venues including the American Geophysical Union and the Royal Society as an analogue to rapid carbon cycle perturbations.

Chronology and subdivisions

Stratigraphic work divides the interval into an onset, peak, and recovery over timescales of thousands to hundreds of thousands of years as constrained by radiometric dating at laboratories such as Lawrence Berkeley National Laboratory and cyclostratigraphy applied by teams affiliated with ETH Zurich and the Woods Hole Oceanographic Institution. High-resolution isotope records from sites like the Bighorn Basin, Fur Formation, and Falkland Plateau reveal sub-events and excursions that researchers correlate with magnetostratigraphy used by groups at the Smithsonian Institution and the British Geological Survey. Biostratigraphic markers from foraminifera and nannoplankton in cores at the Scripps Institution of Oceanography further subdivide the interval into discrete carbon isotope excursion phases.

Causes and mechanisms

Hypotheses implicate rapid injections of ^13C-depleted carbon from sources including methane hydrates on continental margins demonstrated in work by the Lamont–Doherty Earth Observatory, thermogenic methane release associated with seafloor volcanism near the North Atlantic Igneous Province, and destabilization of permafrost in high-latitude basins such as those studied by researchers at the Alfred Wegener Institute. Volcanism linked to plate tectonic reorganizations adjacent to the Iceland plume and greenhouse feedbacks involving water vapor and cloud responses have been modeled by teams at NASA Goddard Institute for Space Studies and the Potsdam Institute for Climate Impact Research. Ocean circulation changes related to gateways like the proto-North Atlantic seaway and carbon cycle feedbacks involving silicate weathering recorded by investigators from University of Cambridge and University of Texas at Austin have been proposed to explain termination.

Climate and environmental impacts

Global mean surface temperatures rose markedly, producing reduced equator-to-pole gradients that altered precipitation patterns in regions such as Greenland, Amazon Basin, and central Eurasia as reconstructed from paleobotanical records curated by the Royal Botanic Gardens, Kew and palynological studies from the Natural History Museum, London. Sea surface temperature increases are inferred from oxygen isotope records in sites sampled by the International Ocean Discovery Program, affecting thermohaline circulation studied by oceanographers at the Woods Hole Oceanographic Institution. Acidification and anoxia events in basins like the Arctic Ocean and Tethys Ocean had consequences for carbonate deposition patterns examined by researchers at the University of Vienna and the Geological Survey of Canada.

Biotic responses and extinctions

Terrestrial faunal turnover included rapid dispersal and evolutionary radiations of mammals recorded in the Bighorn Basin and Himalayan foothill sequences analyzed by paleontologists at the American Museum of Natural History and the Field Museum. Floral assemblages shifted toward thermophilic taxa in deposits studied by the Smithsonian Tropical Research Institute and the Chinese Academy of Sciences. Marine extinction selectivity affected benthic foraminifera documented in micropaleontology collections at the Natural History Museum, Paris and the University of Tokyo, while planktonic communities reorganized with consequences traced in microfossil records housed at the British Antarctic Survey.

Geological and geochemical evidence

Carbon isotope excursions in bulk organic carbon and foraminiferal carbonate, first highlighted in cores from the Walvis Ridge and the Blake Nose, provide primary chemostratigraphic evidence. Trace element anomalies including increased barium and boron and shifts in calcium carbonate preservation recorded by analyses at Geoscience Australia and the Geological Survey of Japan support acidification and productivity changes. Sedimentological indicators such as black shales in the Paris Basin and clay-rich horizons in the Williston Basin document anoxic intervals and enhanced weathering, integrated with magnetostratigraphy calibrated at the Geological Survey of Finland.

Human and scientific significance

The event is a benchmark for understanding rapid carbon cycle perturbations invoked in policy and modeling contexts by organizations such as the Intergovernmental Panel on Climate Change and the National Oceanic and Atmospheric Administration. It provides constraints for Earth system models developed at Princeton University and MIT and informs risk assessments discussed at forums like the World Economic Forum. Ongoing interdisciplinary research drawing on paleoclimatology, geochemistry, and paleobiology by consortia including the International Geosphere-Biosphere Programme continues to refine its role as an analogue for modern anthropogenic warming and guides conservation priorities coordinated by entities like the United Nations Environment Programme.

Category:Eocene Category:Paleogene climate events