Dispelling the myth of bipolar glaciation 41 million years ago

Aug 30, 2007

Large continental ice sheets did not exist in both hemispheres around 41 million years ago during the warmer-than modern conditions of the time.

This is the finding of scientists from the University of Southampton's School of Ocean and Earth Science at the National Oceanography Centre, Southampton (NOCS), reported in Nature.

The Eocene epoch (55 to 34 million years ago) was the last interval of sustained global warmth in Earth's history, a likely consequence of atmospheric carbon dioxide levels much higher than today. It has been known for some time that, at the end of the Eocene, ice sheets on Antarctica first expanded to close their modern size. However, in a recent controversial move, it was proposed that, despite the high global temperatures of the time, very large ice sheets existed 8 million years earlier, not just on Antarctica but also in the Northern Hemisphere.

New findings from NOCS researchers show that, if ice sheets did exist during the controversial interval they must have been small and would have been easily accommodated on Antarctica with no need to invoke Northern Hemisphere glaciation. This result is more in keeping with other geological records and climate model results suggesting that the threshold for ice sheet inception would have been crossed earlier in the Southern Hemisphere than in the Northern Hemisphere because the South Pole has a continent sitting over it (Antarctica) while the North Pole has an ocean (the Arctic).

The NOCS group also identifies a short-lived event immediately preceding the controversial interval during which ocean temperatures briefly increased, the deep ocean became more acidic and the carbon cycle was perturbed by the contribution of isotopically light carbon to the ocean/atmosphere system. This finding hints at the operation of carbon cycle processes common to those thought responsible for the famous transient extreme warming events that occurred between 50 and 55 million years ago, providing a focus for future work aimed at better understanding climate-carbon cycle feedbacks.

Kirsty Edgar, Dr Paul Wilson and Philip Sexton of the University of Southampton's School of Ocean and Earth Science, based at NOCS, used stable isotope analysis of fossil shells of foraminifera (microscopic marine organisms) and bulk sediment from deep-sea sediments to generate a record of climate change and estimate potential global ice volumes in the Eocene. Sediment cores were taken in the tropical Atlantic Ocean by the Ocean Drilling Program (ODP).

Source: University of Southampton

Explore further: New tremors raise concern at Japan's Mount Ontake

add to favorites email to friend print save as pdf

Related Stories

Water in the solar system predates the Sun

Sep 25, 2014

Water was crucial to the rise of life on Earth and is also important to evaluating the possibility of life on other planets. Identifying the original source of Earth's water is key to understanding how life-fostering ...

Weathering the storm

Sep 03, 2014

Old-timers sharing childhood stories about growing up in Maine sometimes recount hiking 10 miles uphill in 3 feet of snow to get to school—and home.

Recommended for you

Tropical Storm Rachel dwarfed by developing system 90E

1 hour ago

Tropical Storm Rachel is spinning down west of Mexico's Baja California, and another tropical low pressure area developing off the coast of southwestern Mexico dwarfs the tropical storm. NOAA's GOES-West ...

NASA ocean data shows 'climate dance' of plankton

4 hours ago

The greens and blues of the ocean color from NASA satellite data have provided new insights into how climate and ecosystem processes affect the growth cycles of phytoplankton—microscopic aquatic plants ...

Glaciers in the grand canyon of Mars?

6 hours ago

For decades, planetary geologists have speculated that glaciers might once have crept through Valles Marineris, the 2000-mile-long chasm that constitutes the Grand Canyon of Mars. Using satellite images, ...

NASA support key to glacier mapping efforts

6 hours ago

Thanks in part to support from NASA and the National Science Foundation, scientists have produced the first-ever detailed maps of bedrock beneath glaciers in Greenland and Antarctica. This new data will help ...

User comments : 0