thermohaline circulation experiment

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Oceanography Topical Resources

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Thermohaline Circulation Demonstration

This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the process are

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• First Publication: June 9, 2013
• Reviewed: July 21, 2015 -- Reviewed by the On the Cutting Edge Activity Review Process

This activity helps the students to visualize the effects of temperature and salinity on water density, and the resulting thermohaline circulation. Important processes visualized in this demonstration are upwelling, downwelling, and the formation of haloclines, thermoclines and pycnoclines. In addition, mixing by advection is clearly demonstrated.

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Grade level.

Skills and concepts that students must have mastered

How the activity is situated in the course, content/concepts goals for this activity.

• salinity and temperature as conservative properties and ability to predict the salinity and temperature of a mixture if the proportions are known
• effect of salintiy and temperature on density of water
• upwelling and downwelling processes
• concepts of thermocline, halocline and pycnocline

Higher order thinking skills goals for this activity

• determination of salinity and temperature of a mixture
• prediction of behavior of waters of different salinities and temperatures

Other skills goals for this activity

Description and teaching materials, teaching notes and tips, references and resources.

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Weather in a Tank

A Laboratory Guide to Rotating Tank Fluid Experiments and Atmospheric Phenomena

Thermohaline Circulation: Introduction

Introduction |  Tank – How to | Tank – Examples | Theory | Wiki

Because of the paucity of direct observations of abyssal flow in the ocean, theory and laboratory experiments have been an invaluable guide in deducing likely circulation patterns. There are two important inferences that can be made from ocean observations:

• Dense water is formed at the surface in small, highly localized regions of the ocean in polar seas. Thus the abyssal circulation seems to be induced by local sources. But for every particle of water that sinks, one must return to the surface. Property distributions suggest that the return branch does not occur in one, or a few, geographical locations. It seems reasonable to suppose, therefore, that there is widespread compensating upwelling on the scale of the basin.
• Deep flow is sluggish with very long timescales. It will therefore be in geostrophic, hydrostatic and thermal wind balance.Here we illustrate some of the dynamical principles that underlie the thermohaline circulation of the ocean, driven by sinking of dense fluid formed by surface cooling at polar latitudes. We represent the sphericity of the Earth with a sloping false bottom. The sinking of water at polar latitudes is represented by a source of fluid at the top right-hand-corner of the tank.

Observations of CFCÕs at a depth of 2km (contoured). Superimposed in red is a snap-shot Ð for 1983 Ð of the CFC distribution at a depth of 2km in the North Atlantic as simulated by a numerical model of ocean circulation and tracer transport. The model results are courtesy of Mick Follows (MIT), the data courtesy of Ray Weiss (Scripps).