How do students use spatial reasoning to make sense of demonstrations in density tanks?

Density tanks can be a teaching tool in meteorology and atmospheric science classes for modeling fundamental concepts that emphasize how fluids of different densities behave when combined. We used density tanks to investigate student use of spatial reasoning while making sense of fluid behavior. A density tank is a rectangular tank with a removable dividing wall. Density tanks can model atmospheric stratification, weather fronts, and internal waves. During our investigation with students, we varied the density of water by varying temperature or salinity and used food color to make apparent these differences. We demonstrated how water of different densities interacted immediately and through time. We worked with 26 students in individual semi-structured, interviews, and asked them to predict what could happen when contrasting colored waters of different densities interact. We combined think-aloud methods with sketching and interactive discussion to prompt student thinking, encourage sense-making, and make spatial reasoning processes visible. We video-recorded and transcribed each session and collected predictive and post sketches. To analyze the data, we used an inductive and comparative method that sought to characterize student spatial reasoning. Our findings suggest that students generally form initial conceptions of density from memories related to food, experiences in the ocean, or early science education. Students had little preconceptions of heat transfer or salt diffusion in water. Students were typically surprised at the initial interactions of the water upon removing the dividing wall and after a minute to an hour. Our work is addressing questions such as " Do misconceptions originate with fluid behavior, heat transfer, or both?" and "On what experiences are students basing their predictions?" These results precede potential inquiries into how students make the conceptual leap between abstract ideas and observable fluid behavior, and how instructors can best use these demonstrations in meteorology and atmospheric science courses.