The oceans act like big heaters, collecting the warmth from the sun and then spreading it all around the world. The currents circle clockwise north of the equator (the imaginary line that circles around the middle of the earth) and counter-clockwise south of the equator. The equator is always warm because the sun shines most directly there. So the currents are always bringing cold water from cold regions (the north and south pole) towards the equator and warm water from the equator towards the poles.
Cold water from the Arctic comes from between Greenland and Baffin Island and flows along the coast of Labrador and Newfoundland into the Atlantic. It is called the Labrador current and at the Grand Banks it meets a warm current called the Gulf Stream. The Gulf Stream current flows out of the Gulf of Mexico below the equator and moves north along the coast of North America and then veers off toward Britain.
When you go to the ocean, you will notice that the land doesn’t suddenly drop off where the land meets the water like in a swimming pool. It gets deeper very gradually so that you can run around and swim in the water at an ocean beach. This is called a continental shelf and sometimes it can go a long, long way out before it drops off.
It is like this off the coast of Newfoundland. The ocean is fairly shallow (around 90 metres deep). Here the warm current from the Gulf of Mexico mentioned earlier flows over the shallow shelf and meets the cold waters from Labrador (a temperature difference of up to 26 degrees). This makes the water swirl and mix about and brings up from the bottom silt and minerals that have been carried into the sea by rivers. Since this mixing and swirling causes more water to come to the surface within reach of the sun’s rays, it means more little plants in the water called plankton can grow. Fish like to eat plankton and so many fish come here to eat and that makes it a great place to catch fish.
The rest of the ocean floor has hills and valleys very much like land. Down the middle of the Atlantic are two great plates which are moving apart around a centimetre each year and have formed what is called the mid-Atlantic ridge.
The circling currents create an area in the middle of the western Atlantic that became the source of legends about ships becoming entangled in seaweed and dragged to the bottom. It is called the Sargasso Sea. It is a body of warm surface water half the size of Canada and about half a mile deep floating on the colder and deeper ocean water. The Atlantic is the saltiest ocean, but the Sargasso is even saltier. The water of this sea is deep blue and crystal clear possibly because it contains very little plankton. However, there is a kind of yellow-brown seaweed which grows here called “sargassum”. It doesn’t have a root system like most plants, but instead it’s fronds have little air bladders so that it can float along near the surface. Sometimes it occurs in small bunches and sometimes in masses as large as football fields and several feet deep. This seaweed creates a habitat for many types of ocean life. It is thought that baby sea turtles, once hatched on shore, swim out to the Sargasso Sea to grow up.
PROJECT: Find the Atlantic Ocean on a map. Find out a little about a creature that lives in one of the oceans that surround Canada (ie. narwhal, sea turtle, giant octopus).
Fold a piece of paper into quarters, and then title each quarter:
- Physical characteristics (colour, weight, size, appendages, skin type, teeth, eyes)
- Range and Habitat (What is special about where it lives?)
- Food (what does it eat, how often, how does it get it’s food)
- Offspring (gestation period, how many offspring at a time, how are they fed, how are they protected).
Make jot notes of the information you come across under each category. Finally draw a picture or make a model of your creature and using your jot notes write a little about them and the ocean they live in.
BOOKS: Hello Ocean by Pam Munoz Ryan, Charlesbridge, 2001 (picture book).