Exploring the Ocean Floor

(What’s under all that water?)

For thousands of year, people have explored the ocean. One afteranother, different cultures left the safety of land too establish trade routes and travel to distant lands.

By the late 1700’s all of the coastlines had been mapped. Now people started to get interested in what was under the ocean…

Governments and universities have sponsored many deep ocean explorations, butuntil recently, not much was known about the ocean floor.

Why is studying the ocean so difficult? The ocean is deep, and therefore it:

- is very dark- has a tremendous amount of pressure- is very hard to get to- It is very cold

As humans, we also have a little trouble breathing under water!

While exploring under the ocean’s surface does present some serious challenges, people can use many creative methods and technologies to gather information.

In the late 1700’s. Capt. James Cook and his crew used a simple method to find the depth of the ocean: they lowered a long rope with a weight attached to the end into the water until the weight hit the bottom. They were then able to use the rope to measure the water’s depth.

Do you think this was very accurate?

During WWI, sonar was invented, thus allowing for more accurate ocean floor mapping.

Sonar stands for sound navigation and ranging. It uses sound waves to caluclate the depth of the ocean floor.

Here is how it works: A sound wave is sent from the ship towards the bottom of the ocean. It bounces off the ocean floor back to the ship, where calculations can be done to find the distance it traveled.

What can we assume about the depth of the ocean floor if sound wavestake longer to return?

Other ways of gathering information about the ocean floor are submersibles, satellites gravity mapping.

The latest technology for mapping the ocean floor involves high-techMulti-beam echo-sounders, which send out sound in a fan-like shape to get greater detail, in combination with GPS systems. This allows for very accurate, almost photographicimages of the ocean floor.

So what features have scientists found on the ocean floor?

The bottom of the ocean is not flat. It has all of the same landforms that we haveon dry land.

In fact, the mountain ranges under the ocean are taller than on land, and the canyons are even deeper!

Let’s pretend that we are going on a submarine voyage to explore the ocean floor.

As we leave the shoreline, we would pass over the continental shelf.

The continental shelf is a gently sloping, shallow extension of the actualcontinent.

The continental shelf will suddenly plunge beneath you.This drastic slope is called the continental slope. This is considered the true edge of the continent.

The ocean floor will then level out. This is the abyssal plain.

Watch out! There are some seamounts up ahead. Seamounts are mountains thatare completely underwater.

There can also be mountain ranges under the ocean. The mid-ocean ridge is a continuous mountain range that winds around Earth. ItIs the longest mountain range on Earth.

As you approach the middle of the ocean, you pass over a deep, dark oceantrench. Trenches are the deepest parts of the ocean.

So how were all these landforms on the ocean floor formed?

The Earth’s crust is made up of a series of plates that are constantlyin motion. If two plates push together, they will form mountains.If two plates move apart, hot melted rock , magma, will fill in the gaps, harden and form new land. This process is referred to as sea floor spreading.

Living things will inhabit different ocean levels depending on their biological needs.

Some physical factors that determine where marine organisms live are:

1. Salinity

2. Water temperature

3. Amount of light

4. Dissolved gasses

5. Nutrients

6. Wave action

Scientists classify ocean organisms according to where they live and how they move:

1. Plankton – tiny organisms that live on the surface and are carried by the waves

2. Nekton – free swimming animals that can move throughout the water

3. Benthos – bottom dwelling organisms; many tend to stay in one place throughout their life

All of these organisms are part of the ocean food web.

Plankton tend to be producers, using sunlight to make their own food.

Nekton tend to be consumers; they eat other organisms.

Benthos can be decomposers, breaking down other organisms after they die.

Organisms that live near the shore have to be able to adapt to changes in salinity, temperature and waves.

Organisms that need sunlight and moderate temperatures must live near the ocean’s surface.

Living things deep in the ocean must adapt to darkness, extreme pressure, and cold temperatures. Because of the darkness, some animals have developed bioluminescence, or the ability to create their own light.

Most scientists agree that the deep ocean is the last unexplored frontier on Earth because it is so hard to get to! Who knows what really lives there?

This skeleton washed up on a beach and nobody is quite sure where it came from.

What do you think it is?