Radioactive dating corals
Cold-water (or deep-sea) corals are part of the taxonomic group called Cnidaria, and they are related to animals like sea anemones and jellyfish.
They can live as individuals or as colonies that form extensive reefs.
The two large colonies will be sampled more extensively for lead-210 dating to provide age determinations with minimal uncertainty.
The series of colony tips will be used to relate growth rates within and between colonies and locations on the seamount.
So far, age determination studies have found that deep-sea corals can attain ages anywhere from a hundred to perhaps thousands of years. 2005b : Lead-210 dating bamboo coral (family Isididae) of New Zealand and California.
Age and growth of deep-sea corals is typically determined from outgrowth studies in the field, growth-zone counts in the skeletal structure, a radiometric technique (e.g., lead-210 dating), or a combination of these techniques. Third International Symposium on Deep-Sea Corals: Science and Management.
From a series of lead-210 dating samples taken in that study, and a recent follow up study (Andrews et al.
2005b), support for the older age estimates prevailed. This diagrammatic representation of the decay of lead-210 over time shows that the activity is reduced to half at about 22 years.
They are surprised to learn that corals are also found throughout the world in the ice-cold, dark waters of the deep ocean. These corals feed by waiting for small food particles to flow past, and then use their stinging cells to capture them. These beautiful animals are among the oldest living organisms; some reefs are several thousand years old, and some individual corals live several hundred years. Before researchers can fully understand the importance and sensitivity of these habitat-forming corals of the deep, we need more information about their life history, such as age, growth, and longevity. The reason lead-210 activity decreases is because it slowly decays (a process called radioactive decay) at a known rate — in this case, a half-life of 22.26 years.
(A half-life is the time elapsed for the radioactivity of a substance to fall to half its original value.) To measure this change in radioactivity and relate it to age, researchers take a series of samples from the edge of a skeletal cross section to the center. Scientists used this cross section of bamboo coral, sampled from Davidson Seamount, for lead-210 dating. The series of holes followed circular patterns that could be seen in the growth structure. Age was determined based on the decay of lead-210, from the edge of the cross section to near the center.