This document discusses salinity and its distribution in the oceans. It defines salinity as the amount of dissolved solid material in water, typically expressed in parts per thousand. The main constituents that determine ocean salinity are chloride, sodium, sulfate and magnesium. Salinity varies in different locations from around 33-38‰ in the open ocean to over 300‰ in places like the Dead Sea. Processes like evaporation and ice formation increase salinity while precipitation and melting decrease it. Global patterns of surface salinity are also discussed, with lower salinity at high latitudes and higher salinity in the tropics.

1. Salinity and it’s
distribution
Tanuj Pareek
Kirorimal College
University of Delhi

2. Salinity
Salinity = total amount
of solid material
dissolved in water
Can be determined by
measuring water
conductivity
Typically expressed in
parts per thousand (‰)
Figure 5-15

3. Constituents of ocean salinity
Average seawater
salinity = 35‰
Main constituents
of ocean salinity:
Chloride (Cl–
)
Sodium (Na+
)
Sulfate (SO4
2–
)
Magnesium (Mg2+
)
Figure 5-13

4. Salinity variations
Location/type Salinity
Normal open ocean 33-38‰
Baltic Sea 10‰ (brackish)
Red Sea 42‰ (hypersaline)
Great Salt Lake 280‰
Dead Sea 330‰
Tap water 0.8‰ or less
Premium bottled water 0.3‰

5. Processes affecting seawater
salinity
Processes that decrease seawater salinity:
Precipitation
Runoff
Icebergs melting
Sea ice melting
Processes that increase seawater salinity:
Sea ice forming
Evaporation

6. The hydrologic cycle
Figure 5-19

7. Surface salinity variation
Pattern of surface
salinity:
Lowest in high
latitudes
Highest in the
tropics
Dips at the Equator
Surface processes
help explain pattern
Figure 5-20

8. Surface salinity variation
High latitudes have low surface salinity
High precipitation and runoff
Low evaporation
Tropics have high surface salinity
High evaporation
Low precipitation
Equator has a dip in surface salinity
High precipitation partially offsets high evaporation

9. Global surface salinity
Figure 5-21

10. Salinity variation with depth
Curves for high and
low latitudes begin at
different surface
salinities
Halocline = layer of
rapidly changing
salinity
At depth, salinity is
uniform Figure 5-22

11. Seawater density
Factors affecting seawater density:
Temperature ↑, Density ↓ (inverse relationship)
Salinity ↑, Density ↑
Pressure ↑, Density ↑
Temperature has the greatest influence on
surface seawater density

12. Density and temperature
variations with depth
Figure 5-24

13. Pycnocline and thermocline
Pycnocline = layer of rapidly changing
density
Thermocline = layer of rapidly changing
temperature
Present only in low latitude regions
Barrier to vertical mixing of water and
migration of marine life

14. Ocean layering based on density
Mixed surface layer (surface to 300 meters)
Low density; well mixed by waves, currents, tides
Upper water (300 to 1000 meters)
Intermediate density water containing thermocline,
pycnocline, and halocline (if present)
Deep water (below 1000 meters)
Cold, high density water involved in deep current
movement

15. Seawater desalination
Desalination
methods:
Distillation
Solar
Heat
Electrolysis
Reverse osmosis
Freeze separation
Figure 5-25
Distillation
Reverse
Osmosis
Figure 5-26