What midges can tell us about climate

Non-biting midges (Chironomidae) are a key organism in the Arctic. The larvae is abundant in fresh water and the adult on land. Foto: Gaute Velle

Extrusion of sediment samples cored in the lake. The glaciers on Bylot island, such as C93 in the background, are retreating fast.

Midges are common organisms in many sources of fresh water, ranging from high-altitude glacier runoff streams to the water-lily ponds in the Museum’s botanical garden. The distribution of individual midge species is temperaturedependent, which means that they can be used to reconstruct past temperature profiles. A widely-used method of reconstructing temperatures is to look at bottom sediments sampled from freshwater lakes. These reveal
numerous animal and plant remains, including those of midges, and the species composition in the sediments can tell us something about how warm or cold it has been at different times in the past.

Post-doctoral fellow Gaute Velle has long been interested in the climate of earlier periods, and he wished to use this method to map the distribution of midges in sediments from a large number of Norwegian lakes in order to reconstruct how temperatures evolved over a large area. When he studied samples from individual lakes, however, they turned out to vary widely. It was quite inconceivable that
differences on such a scale could be due solely to local variations in climate. There had to be something unsatisfactory about the method, for it to produce so much “noise” in the results.

Velle’s suspicions were aroused, and he realised that he would have to start looking at the basic ecology of midges. Since the spread in the results was greatest during the coldest periods, and since our knowledge about fauna in Arctic lakes is sparse,
the scientist continued his studies in the Arctic. Together with colleagues from Scandinavia, Germany and Canada, Velle carried out an extensive programme of field studies on Svalbard and in the Canadian Arctic. It has already become quite clear that temperature, although important, is not the only influential environmental factor. The multidisciplinary research group is studying several organisms in the hope of identifying factors of general significance that affect more species than just midges. With the help of the museum’s systematics experts, the project will also lead to improved mapping of Arctic species.

At the same time, a better understanding of the ecology involved could help us to understand both past climate change and how future climate change could affect animal life. In contrast to similar projects elsewhere, the scientists are working in several dimensions simultaneously. They are not only trying to reconstruct the distribution of these species through time, but are also looking at their spatial distribution. The region in which they are working is characterised by glaciers that are in the process of shrinking. Lakes usually form ahead of the glacier front, or “terminus”. Such lakes are left behind when the glaciers shrink, so that the oldest lakes lie furthest from the glacier, while the most recent ones lie close to the
terminus.

The scientists hope that by comparing sediment cores from all these lakes and the
distribution of species today, they will be able to form a picture of species distribution in time and space. There are a number of different factors that affect the distribution of a species. If scientists do not take other factors than temperature into account when they analyse organic material from bottom sediments, they may introduce systematic errors into the temperature curves that they are trying to reconstruct. One important aim of the project is to give scientists a better basis for interpreting the results they obtain using this widely used method.

Now that the fieldwork has been completed, the scientists have gathered a large amount of material that must be identified to species before the results can be analysed. Velle is a member of a research group at the museum that is studying the landscapes and environment of the past. The group is working on scientific aspects of such environments, but much of its material comes from archeological
investigations, and interdisciplinary cooperation between natural and cultural historical disciplines thus plays an important role in these studies.

The article is published in Features 2009/2010

Gaute Velle is a member of a research group at the museum that is studying the landscapes and environment of the past.