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Water SalinitySalt in the water
A salt crystal dissolved in water
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Earth's Oceans are salty|
Imagine, 71 % of Earth is covered by oceans!
Did you ever swim in the ocean?
If your answer is yes you probably found out that the water tasted very different than the tab water at home or the water you buy in the store. It tastes really salty.
Fresh water has dissolved salts in it too, but not nearly as many as ocean water!
When scientists talk about salt in the water they call it salinity.
In oceanography the salinity is not expressed in percent, but in parts per thousand ‰.
Chemical analyses of solutions uses for salinity parts per million ppm.
The salinity of oceans ranges from 35 to 37 ppt.
That's the same as saying 3.5% to 3.7% of ocean water is salt.
How does the salt get in the ocean?
Salinity is key to understanding interactions among the ocean, climate, and water cycle.
Most of the salt in the sea comes from minerals that were part of the land. When rivers flow over rocks, minerals get dissolved by the water. Part of these minerals is salt later deposited by the rivers into our oceans. Other sources of salt are solid and gaseous materials escaping from the Earth's crust through volcanic vents.
When water evaporates, it leaves the salts and other minerals behind. This makes the water left behind more salty.
|When fresh water is added for example by rivers, or precipitation, the salinity of the ocean will decrease. That explains why some oceans are less salty than others Factors like the melting of ice, the inflow of river water, rain, snowfall, evaporation, wind, wave motion and currents affect the salinity.|
How do we measure salinity?|
Salinity is often defined by measuring how well electricity travels through the water. This is called conductivity of the water. Water that has dissolved salt in it will conduct electricity better than water with no dissolved salt. The more salt is dissolved in the water, the better the water conducts electricity. The salt content of the water can be measured very precisely using the conductivity method. Scientists measure salinity using a CTD Instrument. The abbreviation stands for conductivity, temperature, depth.
Salinity can also be measured with a hand held refractometer. A refractometer measures the change of direction or bending of the light when it passes from air to water. Light moves slower in water than in air. The more salt is in the water, the slower the light moves.
You can see the effect of light bending also called refracting when it passes from the water into the air by putting a pencil in a glass of water.
It looks like the pencil bends where it enters the water. But the pencil is not really bent. The light we see has bent as it moves from water to air.
Hydrometer often used|
to test the water in
of the salinity of the
aquarium water is good
for the fish.
Hydrometer - The specific gravity or relative density of a liquid can be measured.
All water contains dissolved chemicals and minerals that are referred to as "salts".
Talking about salt in the water:
About 90 percent of the salt is called sodium chloride, or ordinary table salt.
Chlorine + Sodium
Magnesium + Sulfur
Calcium + Potassium
are the other major dis-solvents of our ocean.
1 cubic foot of seawater contains about 2.2 pounds of salt, but 1 cubic foot of fresh water from Lake Superior contains 0.01 pound of salt, or about one sixth of an ounce.|
That means sea water is about 220 times saltier than a fresh water lake.
Seawater is a lot saltier than the water in the rivers.
Protecting the flow of freshwater to estuaries is critically important. A special amount of freshwater is needed to ensure rivers continue to maintain historical salinity patterns in estuaries. Dams and using huge amounts of river water for irrigation have already disturbed this balance in many places!
WHY is the right salinity in estuaries so important?
Imagine: A fish lays its eggs onto the ground. With the right salinity these eggs stay there and after a while young fish will be born.
Imagine: The salinity is changing. The eggs on the ground are lifted up, floating on the surface, not protected anymore. A lot of animals will eat the eggs.
In consequence: NO young fish, the next fish generation is killed.
Another problem occurs when salty water enters surface waters through groundwater systems. This saltwater intrusion is seen often when groundwater is pumped for use as public water supply, allowing saltwater to migrate inland.
We need to conserve groundwater resources -water conservation on land is critical to protecting life in rivers and oceans!
What we show know about salinity|
Salt affects water’s freezing point. That is the reason we put salt on roads as a de-icing mechanism.
Salt affects the Earth's ocean currents. The North Atlantic is a key area for sinking of dense, cold, high-salinity water masses that drive "thermohaline" = temperature-salinity circulation. Earth's climate is affected by these ocean currents.
Icebergs form in polar regions & are made of fresh water. Sea ice is frozen seawater has zero salinity = fresh water. Melting icebergs change salinity.
El Niño and La Niña are both influenced by ocean salinity
Ocean salinity is changed by hurricanes which dump hundreds of trillions of gallons of freshwater on the ocean surface.
Lets have a Quiz about salinity|
What do you think?
Which lake has more salt in it?
Lake Michigan or the lake next to Salt Lake City?
Yes, Salt Lake City got its name from its salty lake
300 times more salty than Lake Michigan
What do you think?
Why is sea water less salty near the equator?
Water is less salty because of the abundance of equatorial precipitation throughout the year.
What do you think?
Why is the salinity of the seawater lower towards the poles?
The salinity of water is lower because the salt water around the poles is diluted by melting ice. Additionally, there is only little evaporation in these areas.
What do you think?
Where do we find the most salty water?
The saltiest water with 40 o/oo occurs in the Red Sea, where evaporation is very high and only a little bit of new water comes from rain and rivers.
Why do we need to protect Nature?
What you can clearly see:
Water, rivers are beautiful!
Rivers transport water to the next lake, next stream, always ending up in an ocean or sea!
Along these water lines and shores we can relax, play, watch the birds, discover aquatic plants, enjoy nature and have a good time with family and friends..
That's why it is important to protect water - without healthy water Nature cannot exist!
Nature Conservation protects the water, the plants that need water, the animals and humans that only can live a few days without good drinking water!!
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