Ancient Greenland Was Green
5 Jul, 2007 08:00 pm
Eske Willerslev's study published today in Science overturns all previous assumptions about biological life and the climate in ancient Greenland.
What did the DNA you study reveal?
It revealed that around between 450,000 and 800,000 there was a conifer forest in south central Greenland. That is today covered with more than two-kilometer thick ice. It’s the oldest evidence of DNA, and it’s also the youngest evidence of conifer forest in Greenland.
Figure: Drawing of reconstruction of ancient Greenland by Bent Jærdig Knudsen
How did you find this DNA fossil?
We looked at the silty ice, which is the dirty ice close to bedrock. When people drill holes for climatic studies they drill all the way from the top of the icecap down to the bedrock, which is several kilometers. They use all this clean ice to do measurements for climate change. In the basal part, in the last few meters, there are sediments preserved from underneath the icecap. Our thought was, ‘Is it possible that this sediment could actually contain sediment from some of the animals and plants that were living in Greenland prior to the last glaciations of the area. We found that these sediments do contain DNA from various plants like spruce and pine, but also different types of insects like butterflies, beetles, moths, etc.
What are the implications of this discovery in terms of climate theories?
There are two important implications. First, it is quite surprising to many people, but around 10% of the terrestrial surface is covered with icecaps and glaciers. For these areas we have very limited knowledge about what the biology was like prior to the glaciations. That, for example, is also the situation for Antarctica, which is a huge area. Therefore, because everything is covered by kilometer thick ice it’s not possible to retrieve any fossils to provide any information. Also, because numerous ice cores have been drilled all over the world, what our results imply are that you can take the basal parts of those ice cores, do DNA extractions and amplifications, and then based on the DNA you can identify what plants and animals were present in these areas.
It also has some climatic implications, and you can say that there are two different types of them. First, if you go to Greenland, for example when you study ice cores, you can only go back to maximal 250,000 years. After that it is no longer possible to get a very good age estimate on the clean ice. In our study, from the biology we can say something about how the climate was in Greenland back between 450,000 and 800,000 years, because when we find plants like taxus we know that winter temperatures could not have been below more than –17 degrees Celsius. Because we find these different conifer trees we also know that the summer temperature could not have been below +10 degrees Celsius. So it had been considerably warmer than what is case in Greenland today.
Secondly, we actually got some quite surprising and novel results in terms of current knowledge, because we dated directly silty ice at the base of the ice cap or glacier. Previously people had normally modeled how much of the Greenland ice sheet would disappear during global warming. If you go back, for example, to the last interglacial 120,000 years ago, people had predicted that the temperature in Greenland was 5 degrees higher than today. People predicted that during that stage the Southern Greenland ice sheet basically disappeared – melted and contributed to the sea level rise. What our data suggests is that ice did not completely melt away during this last interglacial. Actually you have to go back much further back to between 450,000 and 800,000. That basically implies that this Southern Greenland ice sheet, which is normally the most unstable part of the Greenland ice sheet, is not as unstable as previously thought. There was melting, but it didn’t melt completely even though there was a difference of 5 degrees in temperature.
Interview by: Christopher Le Coq
Eske Willerslev is a professor of evolutionary biology in the Department of Biology at the University of Copenhagen, Denmark.
Reference: Science 6 July 2007 Vol 317, Issue 5834, Pages 13-133