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chemical property > oxygen isotope ratio

Preferred term

oxygen isotope ratio  

Definition

  • The oxygen isotope ratio is the ratio of lighter isotope 16O to the heavier isotope 18O. The formation of a water molecule occurs from both the isotopes. The lighter isotope (16O) evaporates readily than the heavier isotope (18O) from the ocean. Therefore, the amount of the lighter isotope (16O) in the precipitation is higher, which is why the glacial ice also contains a higher concentration of 16O. Due to this, the higher concentration of the heavier isotope (18O) is left behind in the ocean water. Thus, during the extensive glacial periods, the lighter isotope 16O is tied up in the form of ice, and the concentration of heavier isotope (18O) in seawater increases. But during the warmer period, the glacial ice melts and releases a huge amount of 16O to the sea, which decreases the relative proportion of 18O to the 16O. These records of the ratio of two isotopes (18O/16O) could help determine climate change by identifying the glacial and interglacial periods. We do have these records in the form of ocean sediments. There are some microorganisms that secrete calcium carbonate shells where the prevailing dominant oxygen isotope is utilized. If that microorganism belongs to the glacial period, it uses more 18O, and if it belongs to the warmer period, it utilizes 16O. This 18O/16O can be identified from the composition of the shells made up of calcium carbonate because when the shells of such organisms settle down to the floor, they form the sedimentary layers. Therefore, the oxygen isotope ratio present in the shells of the organism can be useful in determining glacial periods and, hence, climate change. The 18O/16O ratio also changes with the change in temperature. When the temperature is higher, more 18O is evaporated, and when the temperature is lower, its evaporation is less. Thus, the higher temperature increases the heavier isotope concentration, making it abundant in the precipitation of warm eras. Conversely, in the colder periods, the heavier isotope is less productive. The above principle is used to study the ice and snow layers deposited in the glaciers. These depositions represent a record of changes in past temperatures. (Adapted from: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/oxygen-isotope-ratio)

Broader concept

Entry terms

  • oxygen-isotope ratio

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http://data.loterre.fr/ark:/67375/QX8-V4B6C4DM-Z

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