What is oceanography and what are its four branches?
Biological oceanography –- sometimes called marine biology
Chemical oceanography
Physical oceanography
Geological oceanography
What percentage of the Earth is covered with water?
You may already know that water covers about 71 percent of the Earth’s surface.
What is the deepest point in any ocean and it’s average depth?
The deepest known point in any ocean is the Challenger Deep in the Mariana Trench in the Pacific Ocean.
The average depth of the entire ocean
The average depth of the entire ocean is 3,730 metres/12,238 feet.
Why do oceanographers argue that the earth is really covered by one large ocean, rather than being divided into several oceans?
All water on our planet is connected through global hydrologic cycle and ocean currents.
What is the hydrologic cycle and what is its relevance to divers?
Water travels in what is called the hydrologic cycle. This cycle is continuous and shows the movement of water around the Earth. Water is constantly changing from liquid to solid to gas and back again.
Solar heat evaporates water into the air from primarily the ocean, but also from rivers, lakes, and land. Some water vapor also enters the atmosphere from plants in a process called “transpiration” – the passage of water vapor from living organisms.
The atmospheric moisture spreads over the surface of the planet and condenses into clouds before falling again as precipitation – rain or snow. Precipitation is the main source of fresh water in rivers, lakes, and on the ground.
Runoff and ground water ultimately returns the water to the ocean.
What two influences, vital to life, do the oceans produce?
The weather and world climate patterns dictate how warm, cold, wet, or dry it will be. Because of this, the ocean largely determines what organisms live on land, and where.
Important resources such as food and oxygen, and natural resources, such as oil. For divers, the oceans also provide untold hours of recreation and exploration
How do the oceans influence the world’s climate and weather?
The oceans carry heat to areas that would otherwise be cooler and absorb heat in areas that would otherwise be hotter.
Why does ice float and how is this important to life on Earth?
As water cools below the point of maximum density, it begins to crystallize into ice. As water moves into a solid state, it becomes less dense.
If ice sank, ponds, lakes and even oceans would freeze solid, killing most aquatic life as we know it. Surface ice actually insulates the water below, allowing life to thrive.
What is a thermocline and how does it affect divers?
Relatively warm, low-density surface waters are separated from cool, high-density deep waters by a “thermocline,” the zone in which temperature changes rapidly with depth.
Differences in water temperature and salinity cause differences in water density, which causes water to separate into layers. Low-density surface waters are separated from cool, high-density deep waters.
What is a halocline, how is it formed and how does it affect divers?
Besides temperature, water can form layers characterized by an abrupt change in salinity. The interface between these two layers is called a “halocline.”
This is common where fresh water from the land forms a layer over salt water from the ocean.
Why is it important that ice floats on water? (Choose all that apply.)
If ice sank, ponds, lakes and even oceans would freeze solid, killing most aquatic life as we know it. Surface ice actually insulates the water below, allowing life to thrive.
What forces are responsible for currents and what influences current direction?
Essentially, currents are flowing masses of water within a body of water. Large, global currents are caused primarily by the influence of surface winds and variations in water density. Wind transfers momentum to the water it blows across by creating friction on the water’s surface.
The rotation of the earth is another factor in creating currents. Currents rotate in an opposite direction in the northern and southern hemispheres.
In most circumstances, which way should a diver go when there’s a mild current present?
When there’s a mild current at a dive site, begin your dive by slowly swimming into the current so that at the end of the dive, instead of fighting to get back to the boat or shore, the current assists your return.
What makes upwelling and downwelling occur, what biological effects do they have and how do they affect divers?
In addition to horizontal water flow, wind-driven currents sometimes cause a vertical flow called upwelling or downwelling.
An** upwelling is an upward vertical current that brings deep water to the surface**. A downwelling is a downward vertical current that pushes surface water deeper into the ocean. Wind blowing offshore could cause an upwelling, while wind blowing onshore may cause a downwelling.
What biological effects does upwelling and downwelling have
Upwelling and downwelling have** strong biological effects.**
An upwelling tends to bring nutrients up into shallow water. This can significantly increase biological productivity, often on a large scale. For example, the productive fishing grounds off the South American west coast exist because of frequent upwelling.
The biological effect of** downwelling is to carry nutrients and other essential materials to the deep ocean.** Normally throughout the ocean, some nutrients are returned to deeper water when they sink. However, surface organisms recycle most of the organic matter before it can sink. Downwelling removes organic nutrients from the surface. The effect may be a reduction in the productivity of some surface species and an increase in the productivity of some bottom species.
What is a rip current, how do you identify one, and how can you avoid and survive a rip current?
A rip current is a strong channel of water flowing away from the shoreline, typically through a surf line.
You can identify a rip current by looking for any of these conditions:
1 A channel of churning, choppy water
2 An area having a notable difference in water color
3 A line of foam, seaweed, or debris moving steadily seaward
4 A break in the incoming wave pattern
As a diver, if you are caught in a strong rip current, ride the current and swim to the side. Do not try to swim against the current.
Currents along the west coast of continents flow primarily from cooler regions to warmer. On the east coast, the flow is from tropical, warmer areas to cooler.
The west coasts of continents receive water from cooler regions, while the east coasts are bathed with warmer water from the equatorial area.
What is a wave?
A wave is the transmission of energy through matter – in this case water. When energy moves through water as a wave, the water moves back and forth or rotates, but then the water returns to its original position.
What are the parts of a wave?
The crest is the highest point above the average water level.
The trough is the lowest point.
The height is the vertical distance from the trough to the crest.
Wavelength is the horizontal distance between the identical points on two waves, such as crest to crest.
Period is the time it takes for the same spot on two waves to pass a single point.
Frequency is the number of waves that pass a fixed point in one second.
What is the depth at which a wave’s energy can be felt by divers?
At deeper depths, wave energy dissipates until no wave energy is found. The depth at which a wave’s energy can no longer be felt by a diver is about half the wave’s wavelength.
What disturbing forces cause waves?
Disturbing forces that cause ocean waves include:
Wind
Changes in gravity
Seismic activity – undersea landslides and volcanos
Wind is the most common disturbing force. As wind blows over water, friction creates waves.
What is the primary restoring force that resists waves?
Restoring forces that resist ocean wave formation include:
Gravity
Earth’s rotation
Surface tension
Gravity is the main restoring force for large waves and seismic waves. Gravity tends to flatten waves by pulling water back to level.
Gravity and the Earth’s rotation are the primary restoring forces for the tides, because their wavelengths are so long.
What are the three types of waves?
Deepwater Waves These waves occur in water that is deeper than half their wavelength. Water motion in orbital waves decreases very quickly with depth. As you’ve learned, a fish swimming at 18 metres/60 feet would not notice any effects from a wave passing overhead if the wavelength is 36 metres/120 feet or less.
Transitional Waves In depths between one-half and one-twentieth the wavelength, waves are transitional, progressing from deepwater to shallow-water characteristics. At this point, the bottom begins to affect the wave.
Shallow-Water Waves When the depth is about one-twentieth of the wavelength, the wave becomes a shallow-water wave. This is when waves begin to “feel” the bottom forming surf.
