- Q: Why are the oceans salty?
A: According to the U.S. Geological Survey, ocean water is salty because it contains large concentrations of dissolved substances, such as sodium and chloride. The combination of these two elements creates salt. Sodium and chloride account for 90% of all dissolved ions in sea water. Salts and other chemicals found within the Earth's crusts are carried to the ocean via flowing bodies of water such as rivers and streams. Over time, these elements accumulate and increase the water's salinity. As the sun warms the ocean, water near the surface slowly evaporates, leaving behind particles of salt. The freezing of sea ice may also increase salinity. In addition, underwater volcanic eruptions and hydrothermal vents can release dissolved minerals into the sea as well.
To learn more on this topic, please visit:
United States Geological Survey 'Why is the Ocean Salty?'
- Q: Why does pressure increase with depth underwater?
A: An object will feel more pressure underwater than in air because liquid is heavier and denser than air. The deeper you dive, the more water there is to exert greater force. As pressure builds with depth, air molecules become compressed, decreasing in volume and increasing in density. Since our bodies our primarily liquid, we tend to feel this change in pressure around air-filled spaces within bodies such as our ears, sinuses, and lungs.
- Q: How is sound transmitted underwater?
A: The National Oceanic and Atmospheric Administration states that when sound travels underwater, it changes the pressure of its medium. In a liquid medium, sound is transmitted by compressing and decompressing water molecules. Since water molecules are denser than those found in air, sound travels faster underwater. However, water temperature, salinity and depth can affect the speed of sound underwater.
For more information on this topic, please visit:
NOAA Ocean Explorer 'Understanding Ocean Acoustics'
- Q: Why are the oceans blue?
A: The oceans appear blue because they absorb light from the sun. Short wavelengths of light, such as blue, are absorbed the least. This light penetrates the water and is scattered by ripples, oxygen and various ocean particles. Light that is reflected back is observed by the eye as the color blue. Other factors, such as minerals, plants and animals can also affect the color of the ocean.
For more information on this topic, please visit:
NOAA 'The ocean acts like a sunlight filter'
- Q: What is a thermocline?
A: A thermocline is a transitional zone between different layers of
water. Temperature quickly decreases with depth. In the ocean, a thermocline separates the warm, mixed water near the surface from the cold, deeper waters below.
For more information on this topic, please visit:
NASA Earth Observatory-Thermocline
- Q: Why is nautical speed measured in Knots?
A: A knot is a unit of speed that is roughly equal to one nautical mile per hour according to the National Oceanic and Atmospheric Administration (NOAA). Knots are used around the world for maritime and aviation purposes.
In the 17th Century, sailors measured ocean currents with a device called a chip log or common log. A coil of rope with knots spaced equally apart was attached to a piece of wood. The wooden panel was then placed in the water near the back of the boat and the rope was allowed to unwind freely for a specified length of time (30 seconds). When the time had lapsed, sailors would count the number of knots on the rope between the ship and the piece of wood. A ship's speed or the strength of the current was said to be the number of knots counted.
High-tech devices, like Global Positioning Systems (GPS), have replaced the common log, but the term knot is still used for navigation today.
For more information on this topic, please visit:
National Oceanic and Atmospheric Administration - Currents
- Q: What's the difference between an ocean and a sea?
A: Roughly 70 percent of the earth's surface is covered by water. There are four oceans on earth: the Atlantic, the Pacific, the Indian and the Southern Ocean.
According to the National Weather Service, seas (PowerPoint) or smaller bodies of water are "delineated by land masses, whether or not they are largely enclosed." Seas "should also communicate with the ocean." Examples of these smaller bodies of water include the Black Sea and the Mediterranean Sea.
For more information on this topic, please view this PowerPoint presentation:
National Weather Service "The Oceans"
