Stable isotopes and temperature
In this project I have found a very good relationship between temperature and certain particles (stable isotopes) in the skeleton of water beetles. The stable isotopes were measured by myself in a special laboratory.
I used about hundred water beetles from all over North America to do this, but I did not catch them myself. The beetles were given to me by a museum in Ottawa, which I am very grateful for. I used two groups of water beetles, so I could see if there were great differences between different kinds of water beetles. One group is called Helophorus and these are scavengers living at lake bottoms. The other is Hydroporus, which are predators that hunts for their prey.
The temperatures I did not measure myself either, but I got them from weather stations that are located near the place where the water beetles were once collected.
You can see in the graph that the values from isotopes and temperatures make a very nice line. This means that the relation between temperature and stable isotopes in water beetles is very good and that, in turn, means that they can be used to estimate past temperatures.