OCEAN STRATIFICATION
SURFACE AND DEPTH SALINITY
VARIATIONS
• Surface variations
–Varies with latitude
• Lowest at high latitudes
• Highest at tropics of Cancer and
Capricorn
• Dips near the Equator
Surface Variations
• Why vary at the surface?
–High Latitudes: low salinity
• Lots of precipitation
• Melting of ice
• Runoff
• Limited evaporation
Surface Variations
• Why vary at the surface?
–Tropics of Capricorn and Cancer: High
salinity
• Warm air descends here
• Evaporation rates are high
• Little precipitation
• Little runoff
Surface Variation
• Why vary at the surface?
– Equator:
• Warm temperatures
• High evaporation rates
• Increased precipitation
• Increased runoff
• Kind of offset one another
Depth Salinity Variation
• Low latitude regions
– High salinity at surface
– Dips to intermediate level with depth
• High latitude regions
– Low salinity at surface
– Goes to intermediate level with depth
– Approaches value of low latitude version at
depth
• Salinity varies little with ocean depth
The Halocline
• Rapid change in salinity with depth
–Between 300m – 1000m
• Low latitude:
–Curve is a decrease in salinity
• High latitude:
–Curve is an increase in salinity
SEAWATER DENSITY
• Pure water = 1.000g/cm3 at 4°C
• Seawater:
–Dissolved substances increase density
–1.022 – 1.030g/cm3
The ocean is layered
• Ocean Stratification
–Lower density floats on top
–Higher density at bottom
Density is affected by…
• Temperature:
– Density increases as temperature decreases
– Greatest influence
• Salinity:
– Density increases as salinity increases
– Has more effect at poles
• Pressure:
– Density increases as pressure increases
– Least effect
Density curves – low-latitude
• Density remains fairly constant till 300m
– Good surface mixing from currents, waves
and tides
• Below 300m:
– Density increases rapidly with depth to
1000m
• Below 1000m:
– Density remains constant
Density curve – High latitudes
• Very little variation with depth
• High density at surface – low water
temp
• High density below the surface –low
water temp
• Straight line
Pycnocline and Thermocline
• Pycnocline:
– Layer of rapidly changing density with depth
• Thermocline:
– Layer of rapidly changing temperature with
depth
• Typically occurs between 300-1000m
Thermoclines in High Latitudes
• Cold year round surface water
• Thermocline and pycnocline rarely
develop
–Only during the short summer
• Long days of sunlight
–Stays isothermal and isopycnal
Why is it important?
• Pycnocline=barrier to mixing
–Results from combined effects of halo
and thermoclines
–Results in a layered ocean