Earth Science Unit StudyWeek 24: We poured water with varying densities and temperatures together to determine which was the heaviest.
When we visited the ocean in Portugal, there was a significant amount of trash on the beach and we wondered where it came from. Upon returning the book Tracking Trash: Flotsam, Jetsam, and the Science of Ocean Motion (Scientists in the Field Series) provided the answer. When tennis shoes were continuously washed up along the Pacific coast of Washington, one scientist set off in search to discover where they were coming from. He happened to have extensive knowledge of ocean currents, which greatly aided his quest.
As it turns out, the shoes were spilled from a container ship about eight months earlier. This book explains how ocean surface currents work, and how scientists have "Tracked Trash" around the world to learn more about currents.
Did you know that there is an area in the Pacific Ocean filled with floating plastic that is as big as the state of Alaska? It wasn't discovered until the 2000's and scientists are studying its growth and toxic effects. Some of the trash comes from container ships, but much more is thought to have originated on land and arrived by flowing down rivers and streams into the sea. Check out this video and article from the Weather Channel to see how Hawaii is affected by plastic trash.
The trash is all moved by surface currents swirling around in the ocean. Their existence has been known for centuries as they have been used to aid navigation. Like rivers on land they can and do change their course. The Northern Hemisphere contains two main gyres which spin clockwise, and the Southern Hemisphere contains three counter-clockwise spinning gyres. Where the gyres meet, the water traps debris in a never-ending loop thousands of miles across.
Deep Circulation Currents
In addition to the gyres which circulate water on the surface, the ocean contains deep circulation currents which move the water between varying ocean depths. When water freezes at the poles, the remaining water contains more salt and therefore is more dense. As the water increases in density it sinks.
The move Atlas 4D, Hawaii linked below is primarily about Hawaii, but since Hawaii is surrounded by water it includes lots of information about the sea. We watched it as part of this unit study for its outstanding visuals and explanations of deep circulation currents.
Water Density Experiment
Once we had a good understanding of surface currents and deep sea currents, we did an experiment to determine what types of water sink and what types move to the top following Ocean Current Activity - Video Directions.
The book Tracking Trash is one of the best science books I read. If you're studying oceans or Earth science I highly recommend it.
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