1. Salinity, Temperature and Density
Page 19 in your INB

2. Salinity Salinity – the total quantity of dissolved salt in seawater
ON AVERAGE, 3.5% of the weight of seawater is dissolved salt.
We measure salinity as either a percent (3.5%) or in parts per thousand (35ppt)
Keep in mind – this is an average.
Areas where there is a lot of precipitation, freshwater runoff, or thawing of ice have lower salinity
Areas where ice is freezing or water is quickly evaporating have higher salinity,

3. What is salt?
Salt is technically any product of a reaction between an acid and a base.
Salts are held together by an ionic bond.
Ionic bonds form between metals and nonmetals, creating ions of opposite charges that attract each other.
Ions with a positive charge are called cations (Na+)
Ions with a negative charge are called anions (Cl-)

4. Which salts are present in the ocean?
NaCl or table salt is the type of salt we associate with the ocean most often, however other salts exist in seawater.
The most common ions in seawater are called major constituents – they are:
Chloride (Cl-): 55.07%
Sodium (Na+): 30.62%
Sulfate (SO42-): 7.72%
Magnesium (Mg2+): 3.68%
Calcium (Ca2+): 1.17%
Potassium (K+): 1.10%
Less common elements exist in seawater as well. They are called trace elements.
Aluminum, Gold, Copper, Lead, Zinc & many, many more…

5. Where did the salt come from?
Crust and interior of the earth
Earth’s crust is responsible for most of the positively charged cations
Acidic gases released during volcanic eruptions dissolve in rainwater and produce most of the negatively charged anions
The salts are then easily dissolved into seawater due to the polarity of the water molecules.

6. Is salt still being added?
Yes!
Rivers are carrying salts that are less soluble today and adding these salts into the ocean.
This is because the more soluble salts were already carried and added in the past.
Hot water vents located on the seafloor (also known as hydrothermal vents) also cycle salt through their systems.
Salinity of seawater that enters the hydrothermal systems is constant, but when water emerges from the vents the salinity is double! It is unclear now where the extra salt is coming from – this is a current topic of research.

7. What keeps the ocean from getting too salty?
Salt ions are removed…
When sea water as sea spray
when water evaporates
when biological organisms with salt in their systems are harvested
when salt becomes trapped in biological excretions
when biological organisms use salt to make up their shells
Through adsorption – the adherences of ions and molecules onto a particle’s (such as clay’s) surface
The ions then sink and are incorporated into sediment
A ion’s residence time
Residence time is the average time that a substance remains in solution in the ocean.
Sodium for example has a residence time of 210 million years.

8. How do we measure salinity?
Salinity is measured in a variety of ways.
A salinometer measures the conductivity of water. In order to due this correctly, it has to be calibrated to the current temperature.
Buoy systems can be deployed to measure salinity at different depths by checking for conductivity
Refractometers measure salinity by looking at the bending of light waves.
NASA launch the Aquarius satellite in 2011 to measure salinity from space.
Uses microwave radiometer sensor that detects conductivity from space.

9. Aquarius – a cooperative effort between NASA and Argentina to measure ocean salinity

10. Why is ocean salinity important?
Salinity, along with temperature and pressure, impact density.
Density is the mass per unit volume of a substance.
The density of pure water is 1 g/cm3
The density of warm water is less than that of cool water, so warmer water floats on top of cooler water.
The density of water with a high salt content is higher than that of water with a low or no salt content, so low salinity water floats on top of high salinity water.
The density of water controls our ocean’s currents, which control our planet’s climate!

11. Why is ocean salinity important?

12. Salinity and Earth’s climate

13. Key Points
Salinity is the total quantity of dissolved salt in seawater. The average salinity of the Earth’s oceans is 35 ppt or 3.5%
Salts in the ocean are formed through the combination of acids and bases, such as those that occurred during volcanic eruptions.
Common seawater salts are called major constituents. The most common salts are Na+ and Cl-.
Salts are regulated on our planet through biological and physical systems, such as hydrothermal vents or biological usage (shell creation).
Ocean salinity and temperature affect density. Cool, salty water sinks. Warm, fresh water floats.
Ocean density affects ocean currents which affect Earth’s climate.
We monitor salinity by taking conductivity measurements using buoys, salinometers, and satellites.