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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 (THC) in the North Atlantic Ocean and conduct a set of simulation experiments to understand the complex dynamics inherent in this simple model.

Activity takes about 2-3 hours. STELLA software licenses are required.

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Climate Literacy
About Teaching Climate Literacy

Covering 70% of Earth's surface, the ocean exerts a major control on climate by dominating Earth's energy and water cycles. It has the capacity to absorb large amounts of solar energy. Heat and water vapor are redistributed globally through density-driven ocean currents and atmospheric circulation. Changes in ocean circulation caused by tectonic movements or large influxes of fresh water from melting polar ice can lead to significant and even abrupt changes in climate, both locally and on global scales.
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The interconnectedness of Earth’s systems means that a significant change in any one component of the climate system can influence the equilibrium of the entire Earth system. Positive feedback loops can amplify these effects and trigger abrupt changes in the climate system. These complex interactions may result in climate change that is more rapid and on a larger scale than projected by current climate models.
About Teaching Principle 2
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Observations, experiments, and theory are used to construct and refine computer models that represent the climate system and make predictions about its future behavior. Results from these models lead to better understanding of the linkages between the atmosphere-ocean system and climate conditions and inspire more observations and experiments. Over time, this iterative process will result in more reliable projections of future climate conditions.
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Excellence in Environmental Education Guidelines

1. Questioning, Analysis and Interpretation Skills:G) Drawing conclusions and developing explanations
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G) Drawing conclusions and developing explanations.
1. Questioning, Analysis and Interpretation Skills:B) Designing investigations
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B) Designing investigations.
1. Questioning, Analysis and Interpretation Skills:C) Collecting information
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C) Collecting information.
1. Questioning, Analysis and Interpretation Skills:F) Working with models and simulations
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F) Working with models and simulations.
2. Knowledge of Environmental Processes and Systems:2.1 The Earth as a Physical System:A) Processes that shape the Earth
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A) Processes that shape the Earth.
2. Knowledge of Environmental Processes and Systems:2.1 The Earth as a Physical System:C) Energy
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C) Energy.

Benchmarks for Science Literacy
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Transfer of thermal energy between the atmosphere and the land or oceans produces temperature gradients in the atmosphere and the oceans. Regions at different temperatures rise or sink or mix, resulting in winds and ocean currents. These winds and ocean currents, which are also affected by the earth's rotation and the shape of the land, carry thermal energy from warm to cool areas.
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Computer modeling explores the logical consequences of a set of instructions and a set of data. The instructions and data input of a computer model try to represent the real world so the computer can show what would actually happen. In this way, computers assist people in making decisions by simulating the consequences of different possible decisions.
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Notes From Our Reviewers The CLEAN collection is hand-picked and rigorously reviewed for scientific accuracy and classroom effectiveness. Read what our review team had to say about this resource below or learn more about how CLEAN reviews teaching materials
Teaching Tips | Science | Pedagogy | Technical Details

Teaching Tips

  • 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 selected that shows a NASA simulation of the Thermohaline Circulation: http://svs.gsfc.nasa.gov/vis/a000000/a003600/a003658/

About the Science

  • 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 T and S (and delT and delS), and the model includes exchanges with the atmosphere in addition to mixing. The model is simple, yet complex enough to be challenging.

About the Pedagogy

  • The Activity Description/Activity sheet 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 are expected to prepare a report on their findings.
  • The solution set page gives important insights into the behavior of the model for assessment purposes.

Technical Details/Ease of Use

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