The frozen finger pushes into the sediment and bores down into the lake basin. A researcher injects liquid nitrogen into the finger to freeze the sediment, and preserve the sample for examination. During careful analysis of the sediment, researchers discover corn pollen, but this corn pollen is hundreds of years old.
Why is there ancient corn pollen at the bottom of a lake in an area where corn, a farmed vegetable, hasn’t grown? Where did it come from? Who grew the corn close to six centuries ago?
The corn pollen has lain in the sediment at the bottom of Crawford Lake, a Meromictic lake. In a meromictic lake, the water does not completely circulate through the basin at any time of the year, because of the chemical composition of the water or because the deep water is inaccessible to the churning power of the wind. Picture a cone-shape, where the surface area of the lake isn’t large enough to allow the wind to mix the top layers of water with the very bottom layers.
A Meromictic lake is permanently separated into three layers: mixolimnion, chemocline, and the monimolimnion. The mixolimnion is the top layer of the lake, and, like the name suggests, the wind ‘mixes’ this layer. The chemocline is the middle zone between the circulating water on top, the mixolimnion, and the still water of the bottom, the monimolimnion. The chemocline acts like a bordering belt between the warm layer on top and the cold deep water of the bottom. The bottom layer of the lake, the monimolimnion, is too deep for the wind to cycle the water, and the water is too cold to mix with the warmer layers above it. Because of this, the sediment that collects at the bottom, remains there due to lack of circulation. The monimolimnion layer is why the Pollen Corer, nicknamed the Frozen Finger, found centuries old samples of corn pollen left by Iroquoians. The bottom layer consequently has very little dissolved oxygen and this can create ideal conditions for preserving whatever happens to settle along the bottom of a meromictic lake.
Without protection and careful monitoring, this precious discovery, a discovery that lead to a fuller understanding of the history, and the heritage of Halton Region, wouldn’t have occurred. Our water sources not only provide nutrients, but also provide insights into our past; and, conservation areas, such as Crawford Lake preserve, enhance, and share this cultural heritage.
Last modified: March 5, 2019