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Pollen on Lake McDonald 
Photo by Rod Benson
The birds and the bees . . .
This picture, taken in May, shows an abundance of yellow pollen on Lake McDonald in Glacier National Park. Every spring male cones on coniferous trees in the area release million of tiny yellow pollen grains. Some land in larger female cones where they may fertilize the egg cells found there. Once the egg cells have been fertilized, the female cones close up and the fertilized eggs develop into seeds that are eventually released as the cone re-opens.
Like tree rings . . .
Eventually much of the pollen will settle to the bottom of the lake where it will become part of a layer of sediment. During the summer pieces of sand and silt, carried to the lake by streams, settle to the bottom forming a layer of sediment. Tiny particles of clay, also transported by streams remain suspended in the lake until the winter when the lake freezes over. Only then does the water become calm enough to allow these tiny particles to settle. If the sediments aren’t stirred up by waves or burrowing animals, each year will be marked by a sandy summer layer topped by a finer-grained winter layer.
A piece of the puzzle . . .
Pollen grains found in these annual layers can help scientists understand the past climates the area around the lake. Scientists can take core samples from the lake sediment and then analyze them in a laboratory. Based on the type of pollens contained in the sediments, experts can tell what types of plants thrived in the area when specific layers were deposited. Since different plants thrive in different climates, this helps piece together a picture of what the climate was like in years gone by. Lake cores have been found with thousands of annual layers. These layers can also provide clues about the timing of volcanic eruptions that deposited ash in the lake, or earthquakes that disturbed the annual layers.
Right: This photo, provided by the University of Montana, shows Professor Marc Hendrix with a sediment core taken from Flathead Lake. To find out more about what was learned from this coring project, click on the Hot Link below. Also, the September 2004 issue of National Geographic Magazine (pages 58-75) features an extensive article about the use of coring and other techniques to learn about past climates throughout the world. The article inlcludes several interesting photos and graphs.
Below: A closer view of the pollen.
Term: paleoclimatology
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