Question : During the late Ordovician there was a strong positive shift in 18O v
ID: 77467 • Letter: Q
Question
Question:
During the late Ordovician there was a strong positive shift in 18O values over 16O values in oxygen isotopes extracted from brachipod shells. What does this indicate about the climate during this time? Explain your answer.
Interpretation:
Oxygen Isotope ratio cycles are cyclical variations in the ratio of the abundance of oxygen with an atomic mass of 18 to the abundance of oxygen with an atomic mass of 16 present in some substances, such as polar ice or calcite in ocean core samples. The ratio is linked to water temperature of ancient oceans, which in turn reflects ancient climates. Cycles in the ratio mirror climate changes in geologic history. 18O is two neutrons heavier than 16O and causes the water molecule in which it occurs to be heavier by that amount. The addition of more energy is required to vaporize H218O than H216O, and H218O liberates more energy when it condenses. In addition, H216O tends to diffuse more rapidly. As an air mass moves from a warm region to a cold region, water vapor condenses and is removed as precipitation. The precipitation removes H218O, leaving progressively more H216O-rich water vapor. This distillation process causes precipitation to have lower 18O/16O as the temperature decreases.
So an increase in 18O over 16O values would indicate a increase in global temperatures.
Is this correct? Please explain to me your interpretation, with supporting evidence or facts upholding your reasoning.
I feel there is some sort of trick I am not catching.
Explanation / Answer
I think yes its correct because as you mentioned the energy reqiuerment for forming an H2O18 is higher compare to H2O16, So its not favourable thermodynamically. If those climatic conditions any how promtes it then when H2O dissociates itnalso releases to the emviornment which leads to higher climatic tempreture(acc. to III law of thermodynamics).
Again the diffsion of H2O18 is slower compare to H2O16, so if there is an evaporation form oceans which are main source for precipitation(rain and snow), they took longer time to reach the land and ppt.
Sothose condiutions shows high tempreture and low precipitation which is more than enough reason for a global tempreture rise.