Difference between revisions of "Radioisotopes in Corals"

Latest revision as of 17:59, 6 September 2016

Radioisotopes in corals can be used to date fossil corals and as ocean circulation tracers.

Dating of corals

Dating of fossil corals has been done using radioisotopes incorporated within the skeleton at the time of accretion (e.g., ¹⁴C, ²²⁸Ra, ²¹⁰Pb) and those who have grown in since the time of accretion (e.g., ²³⁰Th, ²³¹Pa) ^[1].

Edwards et al. (1986/87) ^[2] revolutionized dating of fossil corals when they developed techniques for measuring ²³⁰Th by using isotope dilution thermal ionization mass spectrometry (TIMS). This method allows to make the measurement on a small amount of material (from tens to 250mg of coral) and reduces the uncertainty on the age estimates compared with the previously used alpha-spectrometry methods. Errors associated with ²³⁰Th age determination are generally less than 1% for samples that are 100 to 200,000 year old ^[3]. Density bands can then be used to obtain annual time control on this "floating" chronologies.

Oceanic Tracers

¹⁴C

Hermatypic Corals growing in the upper 40m of the temperate and tropical oceans (32°N to 32°S) record the input and spatial distribution of ¹⁴C in the oceans. These records provided evidence of past changes in surface-subsurface mixing ^[4][5][6], major current shifts ^[7], and changed in thermocline depth ^[8].

1. ↑ Druffel, E. R. M. (1997). Geochemistry of corals: Proxies of past ocean chemistry, ocean circulation, and climate. Proceeding of the National Academy of Sciences, 94, 8354-8361.
2. ↑ Edwards, R. L., Chen, J. H., & Wasserburg, G. J. (1986/87). ²³⁸U-²³⁴U-²³⁰Th-²³²Th systematics and the precise measurement of time over the past 500,000 years. Earth and Planetary Science Letters, 81, 175-192.
3. ↑ Gagan, M. K., Ayliffe, L. K., Beck, J. W., Cole, J. E., Druffel, E. R. M., Dunbar, R. B., & Schrag, D. P. (2000). New views of tropical paleoclimates from corals. Quaternary Science Reviews, 19(1-5), 45-64. doi:10.1016/S0277-3791(99)00054-2
4. ↑ Nozaki, Y., Rye, D. M., Turekian, K. K., & Dodge, R. E. (1978). 13C and 14C variations in a Bermuda coral. Geophysical Research Letters, 5, 825-828.
5. ↑ Druffel, E. R. M. (1989). Decade time scale variability of ventilation in the North Atlantic determined from high precision measurements of bomb radiocarbon in banded corals. Journal of Geophysical Research, 94, 3271-3285.
6. ↑ Druffel, E. R. M. (1997). Pulses of rapid ventilation in the north Atlantic surface ocean during the past century. Science, 275, 1454-1457.
7. ↑ Druffel, E. R. M., & Griffin, S. (1993). Large variations of surface ocean radioacarbon: evidence of circulation changes in the southwestern Pacific. Journal of Geophysical Research, 98, 20249-20259.
8. ↑ Guilderson, T. P., & Schrag, D. P. (1998). Abrupt shift in subsurface temperatures in the tropical Pacific associated with recent changed in El Niño. Science, 281, 240-243.