OCEAN STRATIFICATION

SURFACE AND DEPTH SALINITY VARIATIONS

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Surface variations

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Varies with latitude

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Lowest at high latitudes

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Highest at tropics of Cancer and Capricorn

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Dips near the Equator

Surface Variations

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Why vary at the surface?

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High Latitudes: low salinity

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Lots of precipitation

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Melting of ice

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Runoff

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Limited evaporation

Surface Variations

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Why vary at the surface?

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Tropics of Capricorn and Cancer: High salinity

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Warm air descends here

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Evaporation rates are high

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Little precipitation

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Little runoff

Surface Variation

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Why vary at the surface?

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Equator:

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Warm temperatures

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High evaporation rates

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Increased precipitation

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Increased runoff

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Kind of offset one another

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Depth Salinity Variation Low latitude regions

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High salinity at surface

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Dips to intermediate level with depth High latitude regions

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Low salinity at surface

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Goes to intermediate level with depth

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Approaches value of low latitude version at depth Salinity varies little with ocean depth

The Halocline

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Rapid change in salinity with depth

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Between 300m – 1000m Low latitude:

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Curve is a decrease in salinity High latitude:

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Curve is an increase in salinity

SEAWATER DENSITY

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Pure water = 1.000g/cm 3 at 4°C Seawater:

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Dissolved substances increase density

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1.022 – 1.030g/cm 3

The ocean is layered

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Ocean Stratification

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Lower density floats on top

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Higher density at bottom

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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

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Density remains fairly constant till 300m

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Good surface mixing from currents, waves and tides Below 300m:

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Density increases rapidly with depth to 1000m Below 1000m:

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Density remains constant

Density curve – High latitudes

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Very little variation with depth High density at surface – low water temp

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High density below the surface –low water temp

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Straight line

Pycnocline and Thermocline

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Pycnocline:

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Layer of rapidly changing density with depth Thermocline:

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Layer of rapidly changing temperature with depth Typically occurs between 300-1000m

Thermoclines in High Latitudes

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Cold year round surface water Thermocline and pycnocline rarely develop

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Only during the short summer

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Long days of sunlight

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Stays isothermal and isopycnal

Why is it important?

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Pycnocline=barrier to mixing

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Results from combined effects of halo and thermoclines

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Results in a layered ocean