Ancient climate change: palm trees give way to spruce

For climatologists, part of the challenge to predict the future is to find out exactly what happened in the past periods of global climate change.

A long-standing climate question is related to the chain of events that occurred 33.5 million years before the end of the Eocene, the early Oligocene. A series of fundamental changes took place. Across the planet, the amount of carbon dioxide decreases rapidly and the warmth of the dinosaur period and the Eocene era ends. In Antarctica, ice sheets formed and covered most of the southern part of the continent.

But what exactly happened on the ground, in the northern hemisphere? How and when does the freeze begin to take place here, and what does answering the question tell us more about the relationship between carbon dioxide levels and today's climate?

An international research group, including Dr. David Greenwood of Brandon University, funded by NSERC, now offers some detailed answers, with information from a special source.

New research reveals information about the age of ancient forests. These are redwoods on Axel Heiberg island, Nunavut. (Photo: copyrighted by David Greenwood)

'Fossils of terrestrial plants are excellent indicators of ancient climate information,' said Dr. Greenwood. 'But the position of fossil trees in the Canadian Arctic and Greenland does not carry information about this climate change, and poses many difficulties in accurately determining their age. Therefore, we have to search for information from another source. '

And that source is the burnt sediment that forms the sediment layer when the North Atlantic begins to expand, and is now at the bottom of the sea between Norway and Greenland today. The core of sediment taken from this area saves a lot of information about spores and pollen being blown from the continent to the west by the wind.

'This sediment core gives us accurate dates for changes in land-dominated plants,' said Dr. Greenwood, 'and many of these plants have relatives. Contemporary objects, so we can assume that their temperature and habitat were similar to today's conditions. '

To get an accurate picture of the transition climate, the researchers combined plant data with material data on the climate and ocean state from isotopic and chemical information. in the same sediment layers, which compares the data with the computer-generated climate model.

'We can see that the summer temperature in the mainland remains relatively warm during the transition from the Eocene to the Oligocene, but the later this period, there is a clear differentiation of different seasons. , ' Dr. Greenwood said.

'It means that the temperature in the coldest month drops by 50C, just above the freezing temperature a bit,' he said

'This may not be enough to turn eastern Greenland into an ice continent,' he said, 'but at least it can wipe out palm trees and other subtropical trees, such as swamp. They are replaced by small leaf trees such as spruce or poisonous plants. '

However, according to the researcher, the temperature is still quite warm in the middle of the transition period. 'Walnuts and commercial plants still exist, but by the end of the period, these two species became very rare,' he explained

According to Dr. Greenwood, although the transition to colder climates has taken place slowly in the Northern Hemisphere, it is an undeniable fact.

'Although the change in the Earth's position in orbit also leads to extreme seasonal radiation changes, and the heat is more concentrated in the tropics, but the main cause is the decline. global amount of carbon dioxide, ' he said.

Records of the research group on the transition from the Eocene century to the Oligocene century will appear in the Nature issue on June 18.

Refer:

James S. Eldrett, David R. Greenwood, Ian C. Harding & Matthew Huber.Increased seasonality through the Eocene to Oligocene transition in northern high latitudes.Nature, 2009;459 (7249): 969 DOI: 10.1038 / nature08069