What is the relationship between benthic 18o and past climate?

Its presence is a good determinant of past hot climates. Its absence can also indicate cold climates.

Explanation:

18O and 16O are oxygen Isotopes, and are used in determining past climates. Heavier than the 16O with 10 neutrons and 8 protons, the 18O does not evaporate as easily and because of this, higher amounts are found in the tropics.

Together, they serve as good determinants of past climate by checking for their ratio in fossils.

Also the 18O isotopes are not present in polar regions as they precipitate before getting to higher altitudes. Cold areas, on the other hand, are high in 16O as they get trapped in glaciers. When climate changes in a location, the quantity of both of these oxygen isotopes also changes.