Modeling the oceanic thermohaline circulation with STELLA

Dave Bice, Penn State University, On the Cutting Edge collection, Science Education Resource Center at Carleton College

In this activity for undergraduate students, learners build a highly simplified computer model of thermohaline circulation in the North Atlantic Ocean and conduct a set of simulation experiments to understand the complex dynamics inherent in this simple model.

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Notes from our reviewers

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Educators will need to review this activity carefully to ensure that students are adequately prepared to use this resource. Instructors will have to develop their own activity assessment, since one is not provided. Instructors may wish to have students look at the CLEAN resource that shows a NASA simulation of thermohaline circulation: [http://svs.gsfc.nasa.gov/vis/a000000/a003600/a003658/]
The thermohaline circulation system (THC) of the North Atlantic Ocean is critically important to the climate system since it is involved with the transport of significant amount of heat to high latitudes of the northern hemisphere. This activity describes the construction of and then experimentation with a STELLA model of the THC. The experiments include examinations of the impacts of varying the initial reservoirs, temperature changes, and freshwater pulses. The activity will challenge student's expectations that only complex behaviors come out of complex systems and models. The activity is based on the Stommel 1961 paper (Tellus, 8, 224-230) about thermohaline convection. While not current, this activity can foster a fundamental understanding of THC dynamics. Comments from expert scientist: Deals with highly relevant question of how THC might respond in a warming world. Students experiment with combined effects of temperature and salinity (and changes in those variables), and the model includes exchanges with the atmosphere in addition to mixing. The model is simple, yet complex enough to be challenging.
The activity description provides only an indication of the kind of background that instructors will need to make effective use of this simulation activity. The recipe for the simulation model and the various experiments are tersely described and may prove confusing for educators and learning without sufficient preparation. It is evident that this activity is taken largely unedited from an existing course by the authors. Students will require background instruction on systems dynamics, building models in STELLA, and the components of a model of the thermohaline circulation system of the North Atlantic Ocean. A full recipe is provided. Students work in groups and prepare a report on their findings. The solution set page gives important insights into the behavior of the model for assessment purposes.