For the past three years I have been doing my dissertation research on stable carbon isotopes and their role in paleoclimate reconstruction at archaeological sites.
Basically, archaeologists do lots of radiocarbon dating of old stuff. With every radiocarbon date, they also receive information on the stable carbon isotope ratio of the material. In the case of plants, this can be used to calculate 13C discrimination rates - which can be an indicator of changes in how a plant uses water.
When conditions are nice and there is consistent rainfall/water access, then a plant soaks up that water. With plenty of water, plants can keep tiny breathing holes on their leaves - known as stomata - open. They will breathe in carbon dioxide, then use the light from the sun to split carbon from oxygen. They breathe out the oxygen, and use the carbon for food. However, when conditions get dry, then the story changes. With less water, a plant can't keep its stomata open because then it loses water. As a consequence, less carbon goes into the plant. As a plant begins to go through 'carbon starvation', heaver and heavier isotopes of carbon are used to build plant tissues. It is this change that is encoded in a plant's stable carbon isotope ratios.
It isn't perfect - and it is really noisy. However, lots of scientists have found that this relationship can be used to identify droughts that happened in the past. Stephen Leavitt and Austin Long of the University of Arizona used tree rings to show this effect back in the 1980's, and folks are still using it today.
Archaeologists have gathered massive amounts of stable carbon isotopes from their radiocarbon dating of sites, but they haven't yet used this data to reconstruct paleoclimate.
Basically, archaeologists do lots of radiocarbon dating of old stuff. With every radiocarbon date, they also receive information on the stable carbon isotope ratio of the material. In the case of plants, this can be used to calculate 13C discrimination rates - which can be an indicator of changes in how a plant uses water.
When conditions are nice and there is consistent rainfall/water access, then a plant soaks up that water. With plenty of water, plants can keep tiny breathing holes on their leaves - known as stomata - open. They will breathe in carbon dioxide, then use the light from the sun to split carbon from oxygen. They breathe out the oxygen, and use the carbon for food. However, when conditions get dry, then the story changes. With less water, a plant can't keep its stomata open because then it loses water. As a consequence, less carbon goes into the plant. As a plant begins to go through 'carbon starvation', heaver and heavier isotopes of carbon are used to build plant tissues. It is this change that is encoded in a plant's stable carbon isotope ratios.
It isn't perfect - and it is really noisy. However, lots of scientists have found that this relationship can be used to identify droughts that happened in the past. Stephen Leavitt and Austin Long of the University of Arizona used tree rings to show this effect back in the 1980's, and folks are still using it today.
Archaeologists have gathered massive amounts of stable carbon isotopes from their radiocarbon dating of sites, but they haven't yet used this data to reconstruct paleoclimate.