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