Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Salinity, Volume, Temperature, and Sea Level
Name: Mathew
Status: Student
Grade: Other
Location: N/A
Country: Australia
Date: March 2009


Question:
Changes in water temperature impact sea level variations. As water warms, it expands and its volume increases, causing levels to rise. We observe a two-month delay for temperature changes to propagate down. The effects of global warming can thus make themselves felt in the oceans within a few years. The quantity of salts in the water has also an influence on sea level, since it changes the water density. The more salty the water, the denser it is, and the lower the level. With that information in consideration, what would be the best way to test the counter affects of the two processes against each other in a class room environment?



Replies:
You put your hands and mind on a problem that perplexes the best minds in weather and climate studies. It is very difficult (maybe impossible) to make an accurate prediction. There are conflicting trends operating in opposite directions. I do not know of any experiment that could be conducted in a class room environment, given that some of the largest computers in the world are trying to churn out the same answer. Sorry.

Vince Calder


You put your hands and mind on a problem that perplexes the best minds in weather and climate studies. It is very difficult (maybe impossible) to make an accurate prediction. There are conflicting trends operating in opposite directions. I do not know of any experiment that could be conducted in a class room environment, given that some of the largest computers in the world are trying to churn out the same answer. Sorry. No!! I have an idea.

This is a good example of the scientific process (note, I did not say method which I think is an abstraction that does not conform to how scientists really think and work). the idea came to me while I was swimming and was not consciously considering your question -- a light bulb turned on. You still cannot do the "real" experiment using conditions as they exist in oceans, that would require a lot of controlled variables that you cannot control. However, you can do some experiments that illustrate the principles using a cluster of experimental variables. I do not know which will work best, but that is part of the experimental science. Here goes:

The principle here is to use colored salts to track the trajectory of an aqueous solution through another colorless solution (This could be water or brine. The only constraint is that it is transparent and colorless (at least for the preliminary experiments). You could use Cu(SO4)-5H2O (green), KMnO4(purple,very intense) or any other colored salt you can obtain. these two are available in hardware or garden stores. They are very soluble in water so you can control the density of the "marker solution" by dilution. The syringes and needles are available at farm supply stores (used to inject farm animals).

You can measure the density quite accurately using a hypodermic syringe. Fill the syringe with water to a mark on the barrel -- let us say 10 ml -- weigh it. Since the density of water is almost exactly = 1 gm / cm^3 you have calibrated the syringe for volume. Now just fill the syringe to the same mark with the test colored solution (that you decide upon). Weigh that. You now know the density of the marker solution. You could create a density / concentration profile if you wish, but let's stay on track for the moment.

Using the syringe, carefully place a single drop on the "quiet" surface of the water. Finding a "quiet" surface may be more difficult than you might anticipate. Use a stopwatch to time how long it takes for the colored solution to touch the bottom of the water. You will need to test the various amounts of the various solutions to have a convenient time lapse. You do not want it to take 3 hours. Nor do you want it to be 3 seconds. The driving force is the density and the acceleration of gravity.

Now for the reverse experiment. Adjust the concentrations so that the density of the "marker" solution is less than the aqueous (colorless) solution. Measure the density of both.

Using the hypodermic needle, immerse the needle tip until it touches the bottom of the colorless solution. Squeeze out 1 to 3 (to be determined) drops of the (now) less dense colored solution and measure the time it takes for the marker solution to reach the surface of the colorless solution. Here, the test solution is working "against" gravity. In the first experiment, gravity was the driving force causing the more dense solution to drop through the colorless solution.

You can also test what happens if you release a few drops of the marker solution at the bottom of the colorless solution when the marker solution has a density larger than the density than the colorless solution.

The critical parameters for experiments such as these are: 1. Good measurements of the densities. 2. Good temperature control -- do not do this in the hallway!! 3. A sturdy bench top so that the sample is not vibrating/shaking. 4. No significant air flow above and around the apparatus.

These conditions would change the whole nature of the experiment.

Vince Calder



Click here to return to the Environmental and Earth Science Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory