Dating an ancient episode of severe global warmingJune 16, 2011
Using sophisticated methods of dating rocks, a team including University of Southampton researchers based at the National Oceanography Centre, Southampton, have pinned down the timing of the start of an episode of an ancient global warming known as the Paleocene-Eocene thermal maximum (PETM), with implications for the triggering mechanism.
The early part of the Cenozoic era, which started around 65.5 million years ago witnessed a series of transient global warming events called hyperthermals. The most severe of these was the PETM at the Paleocene-Eocene boundary, around 56 million years ago. Over a period of around 20,000 years, a mere blink of the eye in geological terms, ocean temperatures rose globally by approximately 5°C. There is evidence that the concentration of atmospheric carbon oxide increased, but the phenomena that triggered the event remain controversial.
One possibility is that these hyperthermals were driven by cyclic variations in the eccentricity of the Earth's orbit around the sun. At the cycle peaks, increased temperatures could have caused methane hydrate deposits in the deep sea to release large amounts of methane. Some of this potent greenhouse gas would have entered the atmosphere resulting in further intensification of the climatic warming, which would have continued as the methane was fairly rapidly converted into carbon dioxide in the atmosphere.
Alternatively, it may have been geological processes, unrelated to variation in the Earth's orbit, which could have been the culprit for the warming associated with the PETM. In this scenario, magmatism would have caused the baking of marine organic sediments, leading to the massive release of methane and/or carbon dioxide, possibly through hydrothermal vents, thus initiating the global warming which led to the methane release.
"Determining exactly what triggered the PETM requires very accurate dating of the event itself, to determine whether it occurred during a known maximum in the Earth's orbital eccentricity" explains Adam Charles, a University of Southampton PhD student supervised by Dr Ian Harding, and first author of the newly published report.
To getter a better grip on the numerical age of the Paleocene-Eocene boundary, the researchers measured radio-isotopes of uranium and lead in the mineral zircon, found as crystals in two volcanic ash horizons deposited during the PETM. These rocks were collected from two locations in Spitsbergen, the largest island of the Svalbard Archipelago in the Arctic.
Based on their data, the researchers dated the Paleocene-Eocene boundary at between 55.728 and 55.964 million years ago, which they believe to be the most accurate estimate to date. Their analyses indicated that the onset of the PETM, unlike those of other Eocene hyperthermals, did not occur at the peak of a 400 thousand year cycle in the Earth's orbital eccentricity. Instead, it occurred on the falling limb of a cycle when warming by the sun would not have been at a maximum.
"Compared to other early Eocene hyperthermals, it appears that the PETM was triggered by a different mechanism, and thus may have involved volcanism. However, a thorough test of this hypothesis will require further detailed dating studies," Adam concluded.
The researchers are Adam Charles, Ian Harding, Heiko Pälike and John Marshall (Ocean and Earth Science, University of Southampton), Daniel Condon (British Geological Survey), and Ying Cui and Lee Kump (Pennsylvania State University). The research was supported by the Natural Environment Research Council (NERC) and Shell UK, as well as a Philip Leverhulme Prize to Heiko Pälike.
Charles, A. J., Condon, D. J., Harding, I. C., Pälike, H., Marshall, J. E. A., Cui, Y. & Kump, L. Constraints on the numerical age of the Paleocene-Eocene boundary. Geochemistry Geophysics Geosystems 12, Q0AA17, doi:10.1029/2010GC003426
National Oceanography Centre, Southampton (UK)
Related Global Warming Current Events and Global Warming News Articles
Climate study finds evidence of global shift in the 1980s
Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.
No substantive evidence for 'pause' in global warming, study finds
There is no substantive evidence for a 'pause' or 'hiatus' in global warming and the use of those terms is therefore inaccurate, new research from the University of Bristol, UK has found.
Half of all Amazonian tree species may be globally threatened
Forests in the Amazon have been declining since the 1950s, but scientists still have a poor understanding of how this has affected populations of individual species.
Melting Scandinavian ice provides missing link in Europe's final Ice Age story
Molecular-based moisture indicators, remains of midges and climate simulations have provided climate scientists with the final piece to one of the most enduring puzzles of the last Ice Age.
Study: Earth's climate more sensitive to CO2 than previously thought
Ancient climates on Earth may have been more sensitive to carbon dioxide than was previously thought, according to new research from Binghamton University.
Loss of diversity near melting coastal glaciers
Melting glaciers are causing a loss of species diversity among benthos in the coastal waters off the Antarctic Peninsula, impacting an entire seafloor ecosystem.
Idea of slow climate change in the Earth's past misleading
In order to predict how today's ecosystems will react to increasing temperatures over the course of global warming, palaeobiologists study how climate change happened in the earth's history and what the consequences were.
Declining snowpacks may cut many nations' water
Gradual melting of winter snow helps feed water to farms, cities and ecosystems across much of the world, but this resource may soon be critically imperiled.
The past shows how abrupt climate shifts affect Earth
New research shows how past abrupt climatic changes in the North Atlantic propagated globally. The study, led by researchers from Centre for Ice and Climate at the University of Copenhagen's Niels Bohr Institute, shows how interaction between heat transport in the ocean and the atmosphere caused the climatic changes to be expressed in different ways across the Southern Hemisphere.
The Greenland ice sheet contains nutrients from precipitation
New research shows that the ice sheet on Greenland contains the nutrient phosphorus, which was carried by the atmosphere across the country, where it fell with precipitation.
More Global Warming Current Events and Global Warming News Articles