Topic: Properties of the Ocean
Theme: Interactions

We have a drastic problem at hand and we are relying on you and your lab assistants to figure this one out!

As you know, we have been at sea a number of weeks exploring the "Properties of the Ocean." Captain Seamore thought it would be a good idea on this last leg of our research cruise to sail into the Gulf of Mexico to the mouth of the Mississippi River. Since our ocean-going research vessel draws (this is how much of the ship is under water when it's sailing on the sea) only 5 meters of water he wanted to try and go up the Mississippi River a short distance and do some data gathering.

Navigation charts of the Mississippi indicate that the river is deep enough to accomodate (handle) our ship. Some parts of the river, however, are only 6 meters deep. Those areas will be a tight fit.

Here's where you and your lab assistants come in!


As we approached the mouth of the Mississippi and attempted to enter, we found we didn't fit. Our ship was drawing more than 5 meters of water. As we sailed back to the Gulf and toward the open ocean, our ship was only drawing 5 meters of water. Again we attempted the Mississippi and again, our ship drew more than 5 meters of water. In other words, we were sitting lower in the water and couldn't get to where we wanted to go in the Mississippi. WHAT IS HAPPENING HERE?

The captain thinks this may have something to do with density. As you are probably aware, there is a difference between fresh water and ocean water. A mouthful of ocean water will give you one obvious difference--ocean water is salty. HOW SALTY IS IT--you ask? Well, that's for you to find out. Better yet, what effect does "how salty" have on the ocean? Are some oceans or bodies of water saltier than others? Why or why not--that is the question.


Your assignment should you choose to accept it, will require that you:

  1. build a hydrometer--a device that allows you to compare the densities of different liquids (not just water) and
  2. use your hydrometer to track the addition of salts to alter density of water.


You will be assessed on your constructed hydrometer, completed data table, and your answers to the questions below:

  • What is an estuary?
  • What happens where rivers meet the sea?
  • Which factors affect the density of ocean water?
  • What is the draft of the boat in fresh water if it is 5 meters in salt water (you may have to use your math here)?

**Note to teachers: The activity we are referring to is Activity 6 (pp. 57-61) in

  • PROJECT EARTH SCIENCE - Physical Oceanography (Won't You BB My Hydrometer: activity 6) - A hands-on activity book for ocean science produced by NSTA

If your students are not ready for this level of activity or you do not own a copy of the above mentioned activity book, we suggest you visit:

  • OCEANWORLD (Density Labs) - an educational website created by the TOPEX/Poseidon Education Team at Texas A&M University through funding by NASA
    Click on "World of Density" and "Density Layering" in the Teacher Workroom under Classroom Activities.

Lesson Ideas created/adapted by Margaret Hammer (Graduate Research Assistant) and Judith Kenworthy (Technology Mentor Fellowship Associate) Texas A&M University. All comments and questions can be directed to stewart@ocean.tamu.edu