Submitted by Anonymous on Sun, 04/08/2007 - 13:45
Forums
Alaska Climate Variation

Hello!

 I was just wondering if you could describe the process of extracting data from lake sediments to determine climatic variations in the last 10,000 years.  What are the steps in this process?

Thanks,

Natasha Bell (student-Spartanburg HS)

Mon, 04/23/2007 - 01:23

Peggy Foletta

Hi Natasha. Good question! Since I am new to this research I have been learning about the process of extracting data from lake sediments, too. The sediments are layered, somewhat like tree rings. As in tree rings which show differences in density of wood produced in spring and summer, producing different colors of spring and summer wood, sediments in lakes can show a variety of cyclic and other changes. Here are some of the methods: 1. During the summer glaciers are melting and the weight of the glacier grinds up the rock below it and coarse particles are washed into the lake which settle onto the bottom of the lake. In winter when the glacier and lake refreeze, the fine particles in the lake settle out. This creates layering of coarse and fine particles indicating the changing seasons.
2. Pollen grains from plants as well as plant remains are found in layers as well. Using a scanning electron microscope the species of the pollen in each layer will determine that type of plants were in the ecosystem at the time, so as the ecosystem changes from cold climate to warm climate or vice versa, this can be determined by how the plant species changed through time as determined by the contents of each layer.
3. Volcanic eruptions deposit tephra which ends up in the sediment. Each volcanic eruption is unique and provides its own ‘fingerprint’.
4. Diatoms which are a major group of algae, are one of the most common types of phytoplankton found in lakes. They are incased in a unique cell wall made of silica. The remains of their shells are deposited in the sediment and the variety of species found in the different layers helps scientists determine the changes in climate in which the assemblages from the different layers lived.
5. Scientists use radioactive carbon dating (and dating of other isotopes) to determine the ages of some of the material mentioned above to help piece together estimates of the time periods of climate changes.