In the study of paleoclimatology and oceanography, which of the following isotopic ratios preserved in marine foraminifera shells is predominantly used to reconstruct past global ice volumes and deep-sea temperatures?

💡 Solution & Explanation

The ratio of oxygen-18 to oxygen-16 in calcium carbonate shells of benthic and planktonic foraminifera serves as a reliable proxy for past global ice volume and water temperature. Lighter oxygen-16 evaporates preferentially and gets locked up in continental ice sheets during glacial periods, enriching the remaining ocean water and foraminifera shells in oxygen-18. Carbon isotope ratios indicate changes in global carbon cycling and primary productivity. Ice cores preserve trapped atmospheric gases for direct paleoclimate reconstruction.