If there is one thing that just about everyone knows about the ocean is that it is salty. The two most common elements in sea water, after oxygen and hydrogen, are sodium and chloride. Sodium and chloride combine to form what we know as table salt.
Sea water salinity is expressed as a ratio of salt (in grams) to liter of water. In sea water there is typically close to 35 grams of dissolved salts in each liter. It is written as 35‰ The normal range of ocean salinity ranges between 33-37 grams per liter (33‰ - 37‰).
But as in weather, where there are areas of high and low pressure, there are areas of high and low salinity. Of the five ocean basins, the Atlantic Ocean is the saltiest. On average, there is a distinct decrease of salinity near the equator and at both poles, although for different reasons.
Near the equator, the tropics receive the most rain on a consistent basis. As a result, the fresh water falling into the ocean helps decrease the salinity of the surface water in that region. As one move toward the poles, the region of rain decreases and with less rain and more sunshine, evaporation increases.
Fresh water, in the form of water vapor, moves from the ocean to the atmosphere through evaporation causing the higher salinity. Toward the poles, fresh water from melting ice decreases the surface salinity once again.
The saltiest locations in the ocean are the regions where evaporation is highest or in large bodies of water where there is no outlet into the ocean. The saltiest ocean water is in the Red Sea and in the Persian Gulf region (around 40‰) due to very high evaporation and little fresh water inflow.
A Funny Bath" - The Dead Sea
No place on earth is like the Dead Sea in the Middle East. Not really a sea but a large lake, the Dead Sea is 47 miles (76 km) long and up to 11 miles (18 km) wide. The name "Dead Sea" was attributed by Christian Monks, when they noticed the absence of any form of life in the salty water.
It is located in the deepest part of the valley that comprises the great Syrian-African rift valley fault. The surface is about 1,300 feet (430 meters) below sea level, the lowest point on earth and varies with each season. It is also very deep with a depth of around 1,300 feet (430 meters).
Fresh water can only flow into the Dead Sea and not out. The only way for water to escape the region is through evaporation. It is estimated that up to seven million tons of water (840,000 gallons) evaporates each day due to the arid climate. Average annual rain fall is only two to four inches (50-100 mm).
When water evaporates, it leaves any impurities behind. As a result, the Dead Sea has the saltiest and most mineral-laden natural water in the world. The surface water has a salinity of about five to nine times that found in the oceans, and the salinity increases with depth. The water of the Dead Sea has a greasy feel to it. The water stings cuts, and causes pain if it comes in contact with the eyes.
At a depth of about 130 feet (40 meters), salinity approaches 300‰, nearly ten times the salinity of the oceans. Below 300 feet (100 meters), though, the water has a salinity of 332‰ and is saturated.
This means the water can hold no more salt in solution and so precipitates out and piles up on the bottom.
The high salinity increases the density of the water which, in turn, makes objects in the water more buoyant. All one needs to do in the Dead Sea is recline and just float.
In fact, it is hard to swim in the Dead Sea because of the buoyancy. Actually people just "hang out".
Mark Twain (1835 - 1910) best described swimming the Dead Sea as he traveled through the Middle East in 1867...
...My face smarted for a couple of hours, but it was partly because I got it badly sun-burned while I was bathing, and staid [sic] in so long that it became plastered over with salt.
It was a funny bath. We could not sink. One could stretch himself at full length on his back, with his arms on his breast, and all of his body above a line drawn from the corner of his jaw past the middle of his side, the middle of his leg and through his ancle [sic] bone, would remain out of water. He could lift his head clear out, if he chose."
"No position can be retained long; you lose your balance and whirl over, first on your back and then on your face, and so on. You can lie comfortably, on your back, with your head out, and your legs out from your knees down, by steadying yourself with your hands. You can sit, with your knees drawn up to your chin and your arms clasped around them, but you are bound to turn over presently, because you are top-heavy in that position."
"You can stand up straight in water that is over your head, and from the middle of your breast upward you will not be wet. But you can not remain so. The water will soon float your feet to the surface. You can not swim on your back and make any progress of any consequence, because your feet stick away above the surface, and there is nothing to propel yourself with but your heels. If you swim on your face, you kick up the water like a stern-wheel boat. You make no headway."
"A horse is so top-heavy that he can neither swim nor stand up in the Dead Sea. He turns over on his side at once."
"Some of us bathed for more than an hour, and then came out coated with salt till we shone like icicles. We scrubbed it off with a coarse towel and rode off with a splendid brand-new smell, though it was one which was not any more disagreeable than those we have been for several weeks enjoying.
It was the variegated villainy and novelty of it that charmed us. Salt crystals glitter in the sun about the shores of the lake. In places they coat the ground like a brilliant crust of ice."M. Twain, The Innocents Abroad
A Funny Taste
We all know the oceans are salty but so are other sources of water. The oceans have a salinity (salt content) of 35‰. The Dead Sea has an average salinity of 290‰, almost nine times saltier than the oceans. But what actually does that mean? Just how salty tasting are these various bodies of water? With up to seven containers of water and table salt, the student a taste of different salinities in various bodies of water around the earth.
|TOTAL TIME||25 minutes.|
|SUPPLIES||7 - 1.5 liter beakers (quart and a half) or larger; 7 sheets of paper; A small drinking cup for each student; 8 liters (2 gallons) of distilled water; One 26-ounce container of salt.|
|PRINTED/AV MATERIAL||Map/globe to show the locations of the various bodies of water.|
|TEACHER PREPARATION||The water and salt solutions (see procedure below) can be prepared before hand or as a classroom participation. The procedure is designed to produce liter size solutions but salt/water amounts can be halved or quartered should lessor amounts be desired.|
|SAFETY FOCUS||Rip Current Safety|
- Write one of the following words on each of the seven sheets of paper: Distilled, Human Tears, The Black Sea, The Oceans, The Red Sea, Great Salt Lake, The Dead Sea.
- Fill each beaker with one liter (one quart) of distilled water and dissolve the proper amount the salt (see table right) in each beaker and place it on the appropriate sheet. (Warming the water in the Great Salt Lake and Dead Sea beakers will help to dissolve the salt.)
- Beginning with the distilled water, place a teaspoon size sample, or less, in each student's drinking cup to allow them to taste it. Repeat with each increasingly salty solution.
Distilled water is water that has been boiled (changed to water vapor) and then recondensed (turns back into a liquid). Water is distilled to purify it of contaminants, like salts, which are left behind.
This same process talks place in the earth's atmosphere. As the sun heats the oceans, water evaporates leaving the salts and other minerals in the ocean behind. In the atmosphere, the water vapor cools and recondenses into tiny water droplets forming clouds.
Given the right conditions, these droplets collided to form larger and larger drops. Finally, when the rising air can no longer support the weight of the drops, the distilled water returns to the earth as rain eventually flowing back into the sea to begin the process all over again.
Just the addition of the different amounts of salt alone will be an eye opening event, especially with the very large amount of salt needed to simulate the Dead Sea's salinity.
For an extended demonstration, place the beakers in a sunny window sill to allow the water to evaporate. Eventually, all that is left will be the original salt.
Since the oceans cover nearly 75% of the earth's surface it is likely your students will visit the beach at least once in their lives. Rip currents are powerful, channeled currents of water flowing away from shore. They typically extend from the shoreline, through the surf zone, and past the line of breaking waves. Rip currents can occur at any beach with breaking waves, including the Great Lakes.
If you see someone in trouble, don't become a victim too:
- Get help from a lifeguard.
- If a lifeguard is not available, have someone call 9-1-1.
- Throw the rip current victim something that floats such as a lifejacket, a cooler, an inflatable ball.
- Yell instructions on how to escape the 'rip'..
Rip Currents: Break The Grip of the Rip!
National Weather Service and National Sea Grant Program, in partnership with the United States Lifesaving Association, are working together to raise awareness about the dangers of rip currents and how to protect yourself.
Before you go to the beach...
- KNOW HOW TO SWIM.
Seems simple enough, but those who do not know how to swim and are pulled out to sea by a rip current stand little chance of survival. And just because you are in shallow water does not mean you are safe either. A person standing waist deep in water can be dragged out into deeper waters, where he/she can drown.
In April 2004, an 19-year-old man was killed by a rip current simply by standing in knee-deep ocean water. Knocked off his feet, this non-swimmer was pulled out to sea and drowned. In 2010, a woman, walking along the shore, was knocked over by a wave, swept out to sea and drowned.
- Check the Surf Zone Forecast for your region.
Surf Zone Forecasts will contain Rip Current Outlooks using the following, three-tiered set of qualifiers:
- Low Risk of rip currents. Wind and/or wave conditions are not expected to support the development of rip currents; however, rip currents can sometimes occur, especially in the vicinity of groins, jetties, and piers. Know how to swim and heed the advice of lifeguards.
- Moderate Risk of rip currents. Wind and/or wave conditions support stronger or more frequent rip currents. Only experienced surf swimmers should enter the water.
- High Risk of rip currents. Wind and/or wave conditions support dangerous rip currents. Rip currents are life-threatening to anyone entering the surf.
When you get to the beach...
- Even just wading in the water is dangerous as a wave can knock you off your feet. If you can't swim, stay out of the water.
- Whenever possible, swim at a lifeguard-protected beach. Ask a lifeguard about the conditions before entering the water. This is part of their job.
- Never, ever swim alone
- Never, ever swim at night. Rip currents can be more dangerous at night simply because you cannot see them like you can during daylight hours.
- Stay at least 100 feet (30 meters) away from piers and jetties. Permanent rip currents often exist along side these structures.
- Use polarized sunglasses. They will help you to spot signatures of rip currents by cutting down glare and reflected sunlight off the ocean's surface.
- Avoid the "it won't/didn't happen to me" syndrome. Obey all instructions/orders from lifeguards and posted signs. They are there for your wellbeing.
If caught in a rip current...
- Remain calm. You will not be pulled under the surface of the water.
- Then only swim parallel to the shore to escape the current. As soon as you are out of the current, only then swim toward the beach. You will not make it swimming directly against the current. It will be too strong for you.
- Another option is to just float. Eventually you will
reach the end of the current. Then either...
- Swim parallel to the shore to get out of the path of the rip current and once you do so, only then swim toward the beach OR
- Draw attention to yourself by waving your arm and yelling for help (which you can do because you are not swimming alone...correct???)
If you see someone in trouble...
- Throw the rip current victim something that floats--a life vest, a cooler, an inflatable ball.
- Get help from a lifeguard. If a lifeguard is not available, call 9-1-1.
- Yell instructions on how to escape the rip current. Tell them which way to swim.
- KNOW HOW TO SWIM.
- Remember, many people drown while trying to save someone else from a rip current
Water has a unique property. As the temperature decreases to 40°F (4°C) the molecules slow, water contracts and the density increases. Below 40°F (4°C) the molecules begin to bond to each other and as they do, the water begins to expand again, decreasing the density. At 32°F (0°C) all molecule are locked into a crystalline structure with a resulting nine percent expansion in size. This expansion, and corresponding decrease in density, is the reason ice floats.
Icebergs are blocks of fresh-water ice that break off, called "calving", from glaciers and float out to sea. Icebergs are found in both the Arctic and Antarctic regions but differ in form and size from each region. Icebergs in the Arctic regions are formed from mountain glaciers and are typically high and narrow.
Called castle bergs, the above-water shapes resemble towers. In the Antarctic, large, and sometime enormous, flat-topped chunks of ice break off off ice shelves and are called tabular bergs. The Arctic produces 10,000 to 50,000 icebergs annually and normally have a four-year life-span.
To be classified as an iceberg, the ice must originate from glaciers or shelf ice. The height must be greater than 15 feet (5 meters) above sea-level, the thickness must be 95-160 feet (30-50 meters), and the area must cover at least 1,500 square feet (500 square meters).
There are smaller pieces of ice known as bergy bits and growlers. Bergy bits and growlers can originate from glaciers or shelf ice, and may also be the result of a large iceberg that has broken up.
Icebergs are typically white or light blue. The white color is from the snow sitting on the berg. The light blue is due to the scattering of blue light, much the same way the sky is blue. However, there are also stripped icebergs in which, during its formation, different colored earthy materials become imbedded in the ice.
A bergy bit is classified as a medium to large fragment of ice. Its height is generally greater than 3 feet (1 meter) but less than 15 feet (5 meters) above sea-level and its area is normally about 300-900 square feet (100-300 square meters).
Growlers are smaller fragments of ice and are roughly the size of a truck or grand piano. They are often transparent but can appear green or black in color. They extend less than 3 feet (1 meter) above the sea surface and occupy an area of about 60 square feet (20 square meters). The green color comes from algae that grows on the submerged portion that becomes exposed when it rolls over into view.
Icebergs are just as much a threat to the shipping industry today as they were in 1912. Ship Masters are weary of even the seemingly smallest pieces of ice near their vessel. As a result of the sinking of the RMS Titanic, U.S. Coast Guard ice patrols were begun to chart the location of icebergs.
Up to World War II, ice patrols were routinely performed by ships. After the war, aerial surveillance became the primary ice reconnaissance method.
Today, it is the basic Coast Guard authority to operated the International Ice Patrol (IIP). Their mission is to monitor iceberg dangers near the Grand Banks of Newfoundland and provide the limits of all known ice to the maritime community. Ships in the vicinity of the "limits of all known ice" normally will pass just to the south of this boundary.
|Growler||<3 ft (<1 m)||<16 ft (<5 m)|
|Bergy Bit||3-13 ft (1-4 m)||15-46 ft (5-14 m)|
|Small||14-50 ft (5-15 m)||47-200 ft (15-60 m)|
|Medium||51-150 ft (16-45 m)||201-400 ft (61-122 m)|
|Large||151-240 ft (46-75 m)||401-670 ft (123-213 m)|
|Very Large||>240 ft (>75 m)||>670 ft (>213 m)|
Vessels passing through the Ice Patrol's published ice limit run the risk of a collision with an iceberg. In this area, the Labrador Current meets the warm Gulf Stream.
The temperature differences between the two water masses can reach up to 36°F (20°C), which often results in dense fog. The combination of icebergs, fog, severe storms, fishing vessels, and busy Trans-Atlantic shipping lanes makes this area one of the most dangerous to navigate through.
Partnered with the International Ice Patrol is the National Ice Center (NIC). The NIC is a unique U.S. government interagency, as it is composed of U.S. Navy, USCG, and NOAA active duty and civilian personnel. While the IIP, through the USCG, monitors iceberg activity in the trans-Atlantic shipping lanes, the NIC monitors iceberg activity around Antarctica. The NIC also provides operational support to the IIP through the USCG year-round.
The amount of salt in sea water also determines the temperature at which sea water freezes. Adding salt to water lowers the freezing temperature. Water with a salinity of 17‰ freezes at about 30°F (-1°C) and 35‰ water freezes at about about 28.5°F (-2°C). Yet, despite the saltiness of the ocean, sea ice contains very little salt, about a tenth of the amount of salt that sea water has. This is because ice will not incorporate sea salt into its crystal structure. Therefore, sea ice is actually drinkable.
We all Scream for Ice Cream
Water freezes at 32°F (0°C). Adding salt to water lowers the freezing point. How low the freezing point goes depends upon the amount of salt in water. The students will make homemade ice cream but the "freezing times" will vary using different amounts of salt to lower the freezing point of water.
- For each pair of students, combine the milk, sugar, and vanilla/chocolate syrup into a sandwich-size baggy and seal closed.
- Have the students shake/squish their baggy for one minute to thoroughly mix the contents.
- Place the baggy inside the larger freezer-size zip-seal plastic baggy and fill that bag one half full with crushed ice.
- In 2 ounce increments, up to 10 ounces, place varying amounts of rock salt in each large baggy. Include a pair or two of students with no salt added.
- Have each pair estimate how long it will take for their mixture to freeze.
- With all students beginning at the same time, have them mix and churn their baggy at a fast pace until the contents have solidified.
- Record their times.
- When finished, dispose of the large bag and eat the ice cream.
The baggies with the most salt should "freeze" first with the bags containing decreasing amounts of salt taking longer. The greater the salt content, the lower the freezing point of the water and therefore the colder saltwater/ice solution becomes generating ice cream quicker.
A common misconceptions is salt makes the ice melt faster. Salt has nothing to do with how quickly the ice melts - it just determines what temperatures it will melt (or freeze). The table (right) provides the average freezing points of water for various bodies of water based on their salinity.
The lowest freezing point for a salt solution is -6.0°F (-21.1°C). At that temperature, the salt begins to crystallize out of solution, along with the ice, until the solution completely freezes. Below -6.0°F (-21.1°C), the frozen solution is a mixture of separate saltwater crystals and fresh water ice crystals, not a uniform mixture of saltwater crystals.
The baggies without any salt will not freeze. Pretty much anything that dissolves in water (or milk) will lower the freezing point; such as sugar. Salt is used on roads because it's inexpensive. Adding sugar to the milk lowered the freezing point to below that of the plain ice (32°F) and therefore will not freeze.
Exposure to cold can cause frostbite or hypothermia and become life-threatening. What constitutes extreme cold varies in different parts of the country. In the Deep South, near freezing temperatures can be considered extreme cold.
Freezing temperatures can cause severe damage to citrus fruit crops and other vegetation. Pipes may freeze and burst in homes that are poorly insulated or without heat. In the North, extreme cold means temperatures well below zero.
Frostbite is damage to body tissue caused by extreme cold. Frostbite causes a loss of feeling and a white or pale appearance in extremities, such as fingers, toes, ear lobes or the tip of the nose.
If symptoms are detected, get medical help immediately! If you must wait for help, slowly rewarm affected areas. However, if the person is also showing signs of hypothermia, warm the body core before the extremities.
The temperature and salinity of the sea water also help determine its density. As the temperature of sea water decreases the density also increases. Also, as the salt content of sea water increases, so does its density. This makes the density of sea water, unlike fresh water, below the freezing point. So in situations of sea ice formation, the salinity, and therefore the density of the underlying water continues to increase well after an area is iced over.
Salt 'n Lighter
Just as air can have different densities, water can have different densities as well. As the salinity of water increases, the density increases as well. Fresh eggs will float saltwater, but will sink in freshwater. This will show that as the salinity increases the density also increases.
- Fill each beaker with one liter of tap water (or each quart jar with one pint of water).
- Add 35 grams of salt to one beaker and 290 grams of salt to a second beaker (½ ounce of salt to one quart jar and 4½ ounces of salt to a second jar).
- Ask the students to speculate in which water solution, if any, will the eggs float.
- Place an egg in each solution and observed which egg floats.
Fresh eggs are more dense than fresh water and therefore will sink. However, as the salt content increases in water, it becomes more dense. The egg will float in the two beakers with the added salt. This happens because the added salt makes the water heavier than the egg causing the egg to float.
The solution with the 35 grams of salt represents the salinity of the oceans. The solution with 290 grams of salt added represents the salinity of the Dead Sea. As the salinity increases, the density increases as well. The egg in the beaker with the most salt should float higher that in the other salty solution.
The increased density of the salty water actually increased the weight of the water. An egg will be buoyant (float) if the weight the egg is less than the weight of the water it displaced. The egg sinks if it weights more than the weight of the water that was displaced.
Ships float for the same reason. Their actual weight is less than the weight of the water that is displaced. Since the weight of the water is greater, ships floats. The following are sizes of some large ships and the weight of the that is displaced.
|Ship||Year Built||Type||Owner||Length (Feet)||Width (Feet)||Weight (Tons)|
|Titanic||1912||Liner||White Star Line||883||92||46,328|
|Enterprise||1962||Aircraft Carrier||United States||1,101||133||89,600|
|Ronald Reagan||2003||Aircraft Carrier||United States||1,092||134||101,000|
|Queen Mary 2||2004||Liner||Cunard||1,132||135||149,000|
|Madrid Maersk||2017||Container ship||Maersk Line||1,309||192||214,000|
|Harmony of the Seas||2016||Cruise ship||Royal Caribbean||1,188||215||227,000|
|Mont*||1981||Supertanker||Amber Development Corp.||1,504||226||647,000|
|*a.k.a. Knock Nevis, Jahre Viking, Happy Giant, Seawise Giant|
Turn Around, Don't Drown
During periods of very heavy rainfall and flash flooding is occurring, many people risk their lives by driving through flooded roads. People erroneously think their "heavy" vehicle will keep them on the road.
Look once again at the size and weight of the ships in the table above. If these vessels float what would make a person think their puny 2 ton vehicle will not float?
When is comes to flooding, just "Turn Around, Don't Drown". https://youtu.be/eI6mIlHKrVY Either find an alternative route to your destination or wait until the water subsides. It is not worth the risk to attempt a crossing of a flooded road!
In the "Average Salinity" map (right), it shows the lowest salinity in the polar regions. Bear in mind, this image depicts surface salinity only. The surface salinity is lower in the polar regions than in the tropical regions due to melting each summer. However, each winter below the ocean surface, the increased salinity in the water due to ice formation, causes the water below the ice to sink and that sinking motion governs the motion of the ocean's deep water currents.
Learning Lesson: Diet Light