L48 Anthro 150A Lecture 9: TA Notes L9
Document Summary
One way is to look at seashells. Foraminifera - really tiny seashell that is made out of calcium carbonate (the presence of oxygen is the most important) Oxygen comes in different types of isotopes - oxygen 16 is a common one; oxygen 18 is more rare (heavier because more neutrons) Lighter isotope evaporates more easily, heavier isotope precipitates more easily. During cold periods, more water trapped as continental ice sheets. These sheets form from atmospheric water, which has more of the lighter isotope. So in cold periods, ocean water is 16o depleted and 18o enriched. Some marine organisms incorporate oceanic oxygen into their shells, preserving the isotopic signal of the ocean water, which in turn reflects global temp. During warm periods, there is more oxygen 16 in the ocean. The marine organisms creating their shells are using a higher proportion of 16o.
