To an extent, the ratio is preserved in the cave rocks, and scientists can use this clue to learn about the climate at the time the rock formed.
Recently, scientists have started to use the oxygen isotope ratio to track changes in the amount of rainfall (heavy rain results in more light oxygen) or changes in where the rain came from—the ocean or inland sources.
When the mineral-rich water drips into caves, it leaves behind solid mineral deposits—the same solid material that forms white spots on water faucets or glass dishes.
The mineral deposits accumulate in the well-known icicle-shaped rock on the ceiling, a stalactite, and in a mound on the floor where the drip lands, a stalagmite.
Because speleothem growth is influenced by geography, ground water chemistry, and other factors, the record from one cave cannot serve as a record of climate change.
Scientists must look for similar patterns of growth in speleothems in caves over a broad area to infer that the climate changed.
Beyond their breath-taking beauty, the formations in Carlsbad and the more than 100 other caves in the area provide a record of rainfall in the southwestern United States.
Less well known, water deposits can also dry in a flat slab called a flowstone.
Geologists refer to the mineral formations in caves as “speleothems.” While the water flows, the speleothems grow in thin, shiny layers.
(Photograph copyright Paul Williams, New Zealand National Institute of Water & Atmospheric Research)Scientists are trying to glean more climate information from speleothems.
The rocks could provide a climate record through the oxygen isotope ratios.
Over time uranium predictably turns into thorium, so scientists can tell how old a layer is by measuring the ratio of uranium to thorium.