1. Easiest way to remember where all water ends up…..
“And though the course may change sometimes, rivers always reach the sea..”
Led Zeppelin, from “Ten Years Gone”

2. Water, the universal Solvent!
Why?

3. Water as a solvent
If you fill a glass with tap water and leave it, notice that after the water has evaporated a stain is left on the glass
If a glass of ocean water is left sitting, the water will evaporate and what will be left? Salt!
These leftovers, called residue, were chemical substances that were dissolved in the water

4. Water as a solvent
Any liquid, including water, that contains dissolved substances is called a solvent
Water is a good solvent because it can dissolve so many substances, and ocean water contains numerous dissolved substances, salt being only one of them
The study of chemical substances found in ocean water is called chemical oceanography

5. Ocean Water Made up of 96.5% water molecules
The remaining 3.5% is mostly salt, which is dissolved in the water
Any substance that is dissolved in a liquid (like water) is called a solute
In ocean water, salt is a solute because it’s dissolved in water, the solvent
This mixture between dissolved salt and water is called a solution

6. Salt (solute)+Water(solvent)=salt water(solution)

7. Ok, time to make YOUR solutions!
Groups of 4 please
Grab a beaker
Fill the beaker about 1/4 with tap water
Pass around the salt
Try to stir in at least 2 to 3 tablespoons of salt
Then, we wait!

8. Substances in Sea Water
Many solutions, like ocean water are called mixtures
A mixture contains 2 or more substances that can be separated by ordinary physical means
For example, if salt water is left to sit – the water will evaporate and the salt will be left!

9. Substances in Sea Water
The salts dissolved in ocean water are called sea salts, and sea salt is a compound
A compound is a substance that contains 2 or more kinds of atoms that are chemically bonded
Salt=sodium+chlorine (Na+Cl)
When salt is added to water, the compound breaks apart, creating charged particles called ions
Na is + charged, while the chlorine becomes a negatively charged chloride ion
Opposites attract!

10. Substances in Sea Water
Another compound found in ocean water is calcium carbonate
This is also called limestone
Calcium carbonate is the main component of seashells and of coral reefs
Again, the wearing down of seashells and coral reefs releases calcium carb into the water, resulting in ions
Calcium is + while carbonate is –
How are ions joined? Electrostatic force!

11. Sea Salts found in Sea Water
Sodium Chloride – 67%
Magnesium Chloride – 14.6%
Sodium Sulfate – 11.6%
Calcium Chloride – 3.5%
Potassium Chloride – 2.2%
Other salts – 1.1%
Remember, when sea water evaporates, all of these salts are left behind as residue!

12. pH pH is the degree of acidity or alkalinity of a solution
Water molecules break up into charged particles called ions
Water=H OH-
In this case, the hydrogen ion is positive, and the negative ion is called the hydroxyl ion
Since opposite charges attract, these ions bond to form water!

13. Moving right along…
When a solution is an acid, it means that it contains a larger amount of hydrogen atoms than hydroxyl atoms
A solution that has a larger number of hydroxyl atoms than hydrogen atoms is called a base, or an alkaline solution
So technically, pH refers to the concentration of hydrogen atoms in a solution
The pH scale! 0-14

14. Acid Rain
Acid rain is formed when chemicals released by the burning of fossil fuels are absorbed by moisture in the air
Many bodies of water can become acidic due to this acid rain, such as rivers and streams – and many have
In extreme cases, these freshwater surface waters can have a pH of 4-5, and can result in massive fish kills
The oceans, however, have a much more stable pH and are less affected by acid rain
Why?
The oceans have much more surface area to dilute the acid rain!

15. Buffers
Furthermore, the oceans have chemicals called buffers that can help maintain a stable pH
Buffers are substances that lessen the acidity or alkalinity of a solution
One of the main buffers in ocean water is the carbonate buffer
Limestone is made from carbonate, and limestone will accept hydrogen ions – so the water will become less acidic and more basic
It can also release hydrogen ions, causing the water to be MORE acidic and less basic
Since it can do both, pH is pretty much kept in check and a balance is maintained

16. Oxygen in the Water
There is oxygen present in ocean water, as well as freshwater surface sources
This is called dissolved oxygen, or DO
Surprisingly, most of Earth’s oxygen supply comes from photosynthesis carried out by algae and plants that live in the photic zones of the water
After oxygen leaves the plants, some dissolves in the water and some is released into the atmosphere

17. Soooo…..
Every time we breathe, we are inhaling some of the oxygen that marine plants and algae release!

18. Oxygen Distribution in Water
Oxygen is not very soluble in water, so the actual quantity is small
Air can hold about 200ppm of oxygen, while water can only hold about 1-12ppm
There is definitely more DO present at the ocean’s surface than in the depths. Why?
Because the photic zone (the zone where light can penetrate) is at the surface, so that’s where photosynthesis by marine plants and algae takes place!

19. Salinity Obviously, ocean water has salt in it!
Does salinity vary in different ocean waters on Earth?
It varies only slightly
In ppt, salinity levels in the Pacific are about 35ppt, while the Atlantic levels are about 37ppt
However, areas like the Red Sea and the Mediterranean are even higher. Why?
They are in areas with hot climate, so there’s more evaporation and less precipitation
So, salinity varies with climate

20. Salinity Salinity also varies with latitude
Salinity is higher at 20 degrees N and S latitude than at the equator. Why?
Regions at the equator have a lot more rain!
A lot of rain will dilute the ocean water, rendering it less salty
Also, on coasts where freshwater rivers or streams enter the oceans salinity is also less

21. Salinity and Depth Salinity also varies with depth
Salinity in the deeper areas is higher than near the surface
At a depth between m is a layer of water called the halocline
This layer shows a rapid increase in salinity, and it continues to increase as depth increases
This is because colder water causes salt ions to move closer together, so it can hold more salt

22. Sources of Salt Freshwater rivers and streams that flow into the ocean
This is because these waters erode streambeds and riverbeds that contain natural salts, and also salts from adjacent land areas enter the streams and rivers in the form of surface runoff
Salt also comes from the ocean floor from hydrothermal vents that emit hot, mineralized water into the oceans
The minerals present in the water include sodium and chloride!