Lab Exercise: Ocean Circulation Simulation: So Far, So Great
In this lab, students learn how ocean dynamics work. Oceans affect or influence just about all life on Earth. It is the special principles of water, in particular its density, that make it possible for oceans to circulate. Wind also acts as an important partner. While density impacts underwater currents, wind drives surface currents.
Students will learn the following: - To understand water dynamics - the ability of water to travel great distances, horizontally and vertically - To create different water masses and see how they interact in a mini-ocean tank - To interpret the basic principles that cause motion via experimentation that simulates the varying properties of water as well as wind.
Context for Use
The format suggested for this lesson is a lab. It's a hands on experiment that should be held in a laboratory setting - or, at the very least, a place where proper precautions are taken (i.e. using plastic drop cloths in the event of a spill). The lab also requires access to electrical outlets.
Description and Teaching Materials
The structure and primary components of this lab lesson is sourced from Columbia University's Earth Environmental Systems Climate (EESC) course, in particular Lab 5: Ocean Circulation.
The following is introductory information intended to provide students unfamiliar with oceans a basic background in order to understand and perform the lab.
The oceans are dynamic – water travels great distances, from the Atlantic to the Pacific, from shallow surface waters down to the deepest, darkest trenches and back up again. Understanding what drives ocean circulation is important because it influences marine ecosystems and is strongly linked to earth's climate. In this experiment, students will create different water masses and see how they interact in a mini-ocean tank. The basic principles that cause motion here are the same as those that drive rising, sinking, and transport in the real ocean
A. Properties of water (H2O)
Water is a really special substance. It can hold a lot of heat, is good at dissolving things, and is essential for life. The density of water is a measure of how much mass is contained in a certain volume. In other words, it's the mass/volume ratio, measured, for example in grams per cubic centimeter). In the ocean, density is controlled by both temperature and salinity. Warmer waters are less dense because the individual water molecules have more energy, bounce off each other, and create more space between molecules. This means that for a certain volume, there is less mass. Salinity is a measure of how much material is dissolved in water – salts, mostly. Salty water is denser than fresh water (pure H2O) because by fitting in between the water molecules, dissolved salts add mass without increasing the total volume. Also, this dissolved material is often charged (positive or negative). Because water is also charged (or "polar"), these molecules are pulled towards each other – this makes seawater denser, because more material is packed into a certain volume.
Water density is important for ocean circulation because dense water sinks.
Surface currents are often driven by wind. Moving air exerts a frictional force on the water surface beneath it, basically dragging it along. Winds influence surface water currents across the globe in many ways that have an impact on ecosystems, fisheries, and marine transportation.
II. THE EXPERIMENT:
Using the given materials (water tank, beakers, salt, ice, food coloring, hair dryers), students design their own experiments. They have three "drivers": salinity, temperature, and wind.
The Experiments Goals are:
1) Create a stratified ocean, with distinct surface, intermediate, and deep-water masses.
2) Cause circulation/motion using density and/or wind (measure velocity during your experiment using stopwatches & rulers).
3) Carefully record your experimental procedure, observe what happens in your tank, and describe/explain it in a lab report.
Students describe the experiment they constructed. What were the initial water mass properties? Describe them in terms of salinity (estimated) and temperature (measured using thermometers). In what order did they add them, and how did they measure the mixing / motion? How did students apply wind?
Students illustrate what they saw in a brief paragraph and drawing(s). On the drawings, label water masses and use arrows to indicate flow direction. Report any measured velocities or other measured quantities in a table/graph. Draw qualitative final vertical profiles of salinity, temperature, and density of the tank (halocline, thermocline, and pycnocline).
· Where do the processes simulated occur in the real ocean?
· How do ocean tank conditions differ from natural conditions? Are there any important missing forces or drivers?
· How did water mass velocities vary, and why?
· Did the tank behave as expected? Discuss any differences between expectations and observations.
Why is what was learned from this experiment important?
E. LAB TIPS
· Write the lab report in the form: Introduction, Procedure/Method, Results, Discussion, Conclusion
· Read the lab instruction carefully and be prepared before coming to the lab:
- You have to understand the fundamentals of ocean circulation before coming to the lab
- Think about how to create different water masses before you come to the lab!!
- Bring with you a camera, stopwatch/cell phone and maybe also a ruler/scale
- Don't forget to make sketches!
· Take care when handling the thermometer (mercury!)
Below are the links for source material and resources:
· EESC course page for Ocean Circulation lecture and lab (accessible to Columbia faculty and students only): https://courseworks.columbia.edu/cms/
· EESC course page that is publicly accessible and contains a 2007 version of the same lab (will be updated this summer with 2011 materials and data): https://eesc.columbia.edu/content/eesc-courses-0
Handouts and Directions:
· Lab instructions
· Water tank
· Food coloring
· Hair dryers
Ocean Circulation Simulation (LAB)
Word version of the module
Teaching Notes and Tips
Background Information for instructors/TAs: Instructors/TAs may find it useful to refer to the following lectures for background information from EESC Spring 2010 (see links above in "Teacher Materials" and below in "References and Resources": · General Circulation of the Ocean (Ting) · Ocean: Wind Driven Circulation and the Gulf Stream (Ting).
Students summarize their findings in a lab report.
References and Resources
Below are the links for source material and resources: · EESC course page for Ocean Circulation lecture and lab (accessible to Columbia faculty and students only): https://courseworks.columbia.edu/cms/ · EESC course page that is publicly accessible and contains a 2007 version of the same lab (will be updated this summer with 2011 materials and data): https://eesc.columbia.edu/content/eesc-courses-0