Wetenschap - 23 juni 2011

Jurassic Campus

The Forum on the Wageningen campus stands on the site of an ice-age swamp. That is not just a wild guess. Paleo-ecologist Bas van Geel reconstructed the history in minute detail, right down to the year.


Foto: .

Well, down to the period at least: what is a century or two between paleo-ecologists, after all? Van Geel, paleo-ecologist and climatologist at the University of Amsterdam (attached to the Institute for Biodiversity of Ecosystem Dynamics, IBED) thinks he knows 'with a high degree of certainty' that the swamp was formed about 50,000 years ago.
'A paleo-ecologist reconstructs developments in the past using remains of plants and animals. So we work mainly with grains of pollen, fungi, algae, seeds, mosses and the like', Van Geel explains in his office at the Science Park in Amsterdam. He is an authority in the field of peat deposits, and the reconstruction of vegetation patterns and the climate that went with them over the last 100,000 years. He came to Wageningen in 2004 after being tipped off by his Wageningen colleague Monique Hiejmans from the Nature Management and Plant Ecology chair group. In the past, they had done research together on raised peat bogs.
Construction started on the Forum in the autumn of 2004. Heijmans: 'I was alerted by a colleague who had seen layers of peat at the building site. I phoned Van Geel about it straightaway.' Van Geel was immediately interested. 'You don't often come across those layers, so you have to make the most of them. They usually lie far too deep. If you do come across them it is just by chance.' After getting an official permit, Van Geel could set to work on 18 October. 'We found a nice spot at the edge of the site and took samples there.'

A picture of climate change
The layer of peat that Van Geel found is positioned roughly between two and a half and four metres underground. Above it, the peat gives way to a lake deposit of about half a metre. The layer full of fossils is wedged in between layers of sand without any plant remains. But that is easily explained, says Van Geel. 'It was just too cold. For extensive periods, nothing grew. During the last ice age, most of the north-west of Europe was a polar desert.'
Geologists speak of the Pleniglacial, the coldest phase of the last ice age. So it was not always as cold as that cold during the last ice age, then? 'There have been several periods of fast warming, followed by relatively slow cooling', explains Van Geel. Those relatively warm phases are known as interstadials. And the deposit containing fossils underneath the Forum is a silent witness to such a period. In fact, what we are looking at here is a natural archive of climate change.
It went more or less as follows. During the fast warming period, the lower-lying parts of the landscape turned into swamps, since rising temperatures brought heavier rainfall. Peat formed in the swamps. The site of the Forum was just such a low-lying part of the landscape. The present Gelderland valley, lined by the moraine of the Heuvelrug and the Veluwe, already existed then too. In fact, the moraine continued uninterrupted through the area where Wageningen now lies.
According to Van Geel, the Netherlands must have looked like a sort of steppe tundra. Of course, there was no Netherlands as such then. Sea levels were about 100 metres lower and Britain was part of the mainland. Van Geel estimates that the average summer temperature was between 5 and 10 degrees Centigrade. 'A continental climate, but less extreme than in the coldest phases of the ice age. It was too cold for trees. You did get dwarf birches and willows.' The odd mammoth probably wandered the steppe here and there. And people? 'Possibly, but they would have been Neanderthals.'

Link with Greenland
The slow cooling period that followed the warming one left the swampy areas under water. Increasing cold put an end to the fun: vegetation disappeared and the wind blew at will. Erosion took place and sand was deposited on low-lying land. And the evidence for all this was found by Van Geel and his team of national and international experts in the 'Forum' deposits. A plethora of micro and macro remains of seeds, leaves, mosses and even mites were dug out of the peat and identified. Admittedly, says Van Geel, there was nothing very special among them. The really special thing was the dating. Van Geel is pretty certain that the Forum layer was formed in a warm period between 54,000 and 47,000 years ago, during one of the 'Dansgaard-Oeschger oscillations'. These temporary periods of warming during the last ice age were named after the two scientists who established a whole series of these sorts of warming periods by studying ice cores on Greenland. Van Geel: 'That is the nice thing about this project: that we have been able to connect what we found with what we know from the ice cores on Greenland.'
Van Geel's work has been on display in the Forum for some time, but you do have to dig around a bit to find it. Tucked away in a corner on the ground floor is a poster on the research. The poster was an idea of Frank Berendse's (Heijmans' boss) and was developed together with the Forum. The photos are well worth making a detour for, bringing you eye to eye with the leaf of the dwarf birch, and all sorts of prehistoric mosses. Specimens that were growing and blooming 50,000 years ago on the spot where we now study, work and eat our midday sandwiches.