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Organic matter in lake sediments is a mixture of biological materials from a number of modern sources plus variable amounts of recycled detrital material. Hence, it is usually difficult to distinguish input variations over time from the diagenesis of organic matter. Comparison of old material of known biological origin with younger material helps resolve this problem. We have compared the compositions of wood and needles from a modern white spruce (Picea glauca) with those from a white spruce buried for 10,000 yr in a lake bottom. Although the tissues are structurally well preserved, some chemical changes are evident in the old samples. Total fatty acid concentrations decrease by over 90%. Sterol and hydrocarbon concentrations are similar in the modern and 10,000-yr-old wood, but the concentration of sterols is lower in the old needles. Cellulose components in the wood have decreased relative to lignin components, although both types of materials remain in high concentration in comparison to other organic components.

Changes in spruce composition following burial in lake sediments for 10,000 yr