What type of oxygen isotope is found in higher concentrations in ocean sediments during warm interglacial times?

• A. Heavy oxygen (18O)
• B. Light oxygen (16O)
• C. Oxygen-17
• D. Oxygen-19

Answer: (B)

Oxygen isotope measurements in marine sediments track past temperature and ice volume. During warm interglacials, ice sheets melt and release more of the light isotope, 16O, back into the ocean. This lowers the relative abundance of the heavy isotope in seawater and in carbonate shells, so the light oxygen becomes more prevalent in ocean sediments. In contrast, colder glacial periods trap more 16O in ice, leaving the ocean and its sediments relatively richer in the heavy isotope, 18O. Therefore, the isotope found in higher concentrations during warm interglacials is the light oxygen, 16O.