An undisturbed sediment core containing varves from the deposition zone of a deep lake

The varves can be used to calculate dates along the core profile

Paleolimnology--Pollen stratigraphy in lake sediment cores

Cores can be dated with radioisotopes

137Cs (half-life 30 yr) is found in fallout from bomb tests

The most commonly used isotope is 210Pb, half-life 22 yr

210Pb

218Po

222Rn

226Ra

238U

The Uranium 238 decay series

The littoral zone, what determines its outer boundary?

The transparency of lake water is measured by its extinction coeficient

The extinction coefficient k increases with:

•the concentration of organic matter (colour) of the water

•the amount of suspended mattereg, phytoplankton, fine suspended particles, eg

clay

Light extinction --Light enters from above and its intensity (I) is sharply attenuated with depth (z)—absorption by water or solute molecules or scattered by particles

Iz

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z 1%

z 10%

Section 10.6

Page 144 in text

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Page 144 in text

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