Salinity refers to the concentration of dissolved ions in water, measured in parts per thousand (‰). Average ocean salinity is 35‰ but it varies depending on evaporation, precipitation, and water sources. Salinity is higher in enclosed seas like the Red Sea (40‰) and Mediterranean Sea (38‰) due to limited freshwater input and high evaporation. It is lower in semi-enclosed seas connected to oceans by narrow straits, like the Black Sea (18‰) and Baltic Sea (8‰), which receive more freshwater from rivers. Temperature, pressure, and density can also impact ocean salinity.

1. Salinity

2. Definition of Salinity
• The concentration of ions in a liter of water
• The number of grams of dissolved solids in
1000 g of water.
– Ex: a 1000 g sample of seawater containing 34.7 g
of dissolved material has a salinity of 34.7 parts
per 1000 g
– In the above example, what is the remaining
96.53%?

3. What units describe salinity?
When we measure salinity, we use these
descriptive terms:
– ‰ = a percent sign with the extra zero to indicate
not parts per hundred, but parts per thousand
– ppt = parts per thousand

4. Variability in Salinity
Even though the proportions of the ions remain the
same throughout the ocean (principal of constant
proportions), the concentration of ions changes
with:
– Evaporation
– Precipitation
Q: what do you think the salinity would look like in the
middle of the ocean, along the equator, compared to
near the edges of the continents?

6. World Ocean Salinity
• Average is 35 ‰
• Red Sea is 40 ‰, Mediterranean Sea is 38 ‰
Q: Why? Look at a map!
• Black Sea is 18 ‰, Baltic Sea is 8 ‰
Q: Why? Look at a map!

7. Variability in Salinity cont.
Other influences on salinity that we’ll cover later:
– Temperature
– Pressure
– Density
Start thinking about how each of these would impact the
salinity of the seawater. . . .