Carbon dating lesson plans
The effect is not necessarily confined to freshwater species—at a river mouth, the outflow may affect marine organisms.
It can also affect terrestrial snails that feed in areas where there is a high chalk content, though no measurable effect has been found for land plants in soil with a high carbonate content—it appears that almost all the carbon for these plants is derived from photosynthesis and not from the soil.
These marine reservoir effects vary over time as well as geographically; for example, there is evidence that during the Younger Dryas, a period of cold climatic conditions about 12,000 years ago, the apparent difference between the age of surface water and the contemporary atmosphere increased from between 400 and 600 years to about 900 years until the climate warmed again. For example, rivers that pass over limestone, which is mostly composed of calcium carbonate, will acquire carbonate ions.During either a geomagnetic reversal or a global polarity excursion, production increases during the period when the geomagnetic field is weak.It is fairly certain, though, that in the last 50,000 years there have been no geomagnetic reversals or global polarity excursions.The known fluctuations in the strength of the earth's magnetic field match up quite well with this oscillation: cosmic rays are deflected by magnetic fields, so when there is a weaker magnetic field, more production and an older apparent age.A secondary oscillation is thought to be caused by variations in sunspot activity, which has two separate periods: a longer-term, 200-year oscillation, and a shorter 11-year cycle.
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If the dates for Akrotiri are confirmed, it would indicate that the volcanic effect in this case was minimal.