Density-driven flow is a major driver of ocean circulation that we introduce to Earth Systems Science students using quantitative tank experiments. Recently, we added an open-ended activity to the lab – challenging students to develop and run experiments of their own design. We use custom-made acrylic tanks that contain a removable barrier which isolates part of the tank. For quantitative experiments the tanks are filled with fresh water and the barrier is used to isolate a small portion. A known amount of salt and dye is added to this volume, creating a more saline, denser water mass. Students, working in teams of 4-5, remove the barrier between the water volumes, observing and timing the progress of the dense salty water as it flows along the base of the tank, to determine the flow velocity. After performing multiple experiments with increasing density, students calculate a constant that allows for the determination of flow velocity as a function of water height and the density contrast between water masses.

Students are then invited to design and conduct an experiment to replicate an ocean process of their choice, based on what they have learned in preceding lectures/workshops. They are provided with materials including salt, ice, warm water, additional barriers, obstacles and fans. This leads to a vibrant engaged class as students attempt to replicate processes such as convergence of currents, ocean stratification, geostrophic flow, the effects of bathymetry and the complex water flow off Antarctica. These experiments provide practice in data recording, writing scientific reports, defining and testing hypotheses, and fitting equations using a spreadsheet. Many students record their experiments as videos or photos, some of which are high-quality demonstrations of science communication and advertisement for the course. Overall, the activity teaches students the link between observations, theory and experimental modelling of oceanographic processes.