Which of the following accurately describes ^18 O / ^16 O ratios of the oceans? Because ^18O evaporates more readily than ^16O. the oceans have a higher relative abundance of ^16O during the summer. The ^18O/^16O ratio in the ocean is low during the winter because temperatures are too low for ^16O to evaporate During the winter. ^16O is high in the ocean; during warmer periods the isotope ratio is lower The ratio of oceanic ^18O/^16O in the late summer is high, because the most of the ^16O has evaporated by then.