Analysis of oxygen isotope ratios in deep ice cores and marine sediment cores is widely used to reconstruct paleoclimates. Which statement correctly describes how the relative abundance of oxygen isotopes (18O^{18}\text{O}18O and 16O^{16}\text{O}16O) indicates historical global temperature variations?
During colder glacial periods, ocean water becomes enriched in 18O^{18}\text{O}18O relative to 16O^{16}\text{O}16O because 16O^{16}\text{O}16O is preferentially evaporated and trapped in terrestrial ice sheets, leading to a higher 18O/16O^{18}\text{O}/^{16}\text{O}18O/16O ratio in marine carbonate shells.
During warmer interglacial periods, glacial meltwater returns high concentrations of 18O^{18}\text{O}18O to the oceans, causing marine sediment cores to show a significantly elevated 18O/16O^{18}\text{O}/^{16}\text{O}18O/16O ratio.
During colder glacial periods, the increased density of polar sea ice prevents the evaporation of 18O^{18}\text{O}18O, resulting in an ice core record that is highly enriched in 18O^{18}\text{O}18O relative to 16O^{16}\text{O}16O.
During warmer interglacial periods, land-based ice sheets preferentially retain 16O^{16}\text{O}16O due to increased atmospheric pressure, resulting in a lower 18O/16O^{18}\text{O}/^{16}\text{O}18O/16O ratio in the ice core layer than in glacial periods.
