A Hands-on Approach to Understanding Stable Isotope Fractionation

Wednesday 1:45pm REC Center Large Ice Overlook Room
Oral Presentation Part of Teaching about Systems


Danielle Schmitt, Princeton University
Stable isotope geochemistry is a standard tool used to study a variety of complex Earth systems. Applications range from using the isotopic composition of shells of calcareous marine microfossils, or gases extracted from ice cores, as climate proxies, to tracing the source of carbon in the atmosphere, to determining the diet of modern and fossil hominids. Understanding the principle of isotopic fractionation is particularly critical to deciphering Earth's past climates as well as the complex processes that govern present day climate.

To give introductory-level students a fundamental understanding of the principles of isotopic fractionation, we use large white beans and small black beans (or peanut and plain M&Ms™) to represent the heavier and lighter isotopes, respectively. Students model several "evaporation" and "precipitation" events by separating the "isotopes," culminating in the formation of an "ice-sheet." Students also use a spreadsheet to formulate equations that describe what is happening in the simulation, and create a simple spreadsheet model to calculate the isotopic ratios and δ18O values of the simulated oceans, clouds, precipitation and ice sheet that result as the activity evolves. After performing the visualization and modeling activities, students move on and use actual δ18O values and relative abundances of microfossils from deep sea sediments to determine relative sea surface temperatures and interpret the history of glacial and interglacial periods.

Prior to performing the visualization activity, students struggled with understanding isotopic fractionation. After completion of the activity they are better able to understand and interpret isotopic data, and extend their understanding to other isotopic systems.

Presentation Media