Horizontal and vertical changes in salinity and temperature:
Salinity
= A measure of the concentration of salt (NaCl). Measured as g per 1000g water (ppt) by
NASA’s Aquarius Satellite.
Freshwater – <0.5ppt
Seawater – 35ppt
Salinity is lowest in the surface zone and increases with depth. It influences water density,
causing this to also increase with depth. Water density affects ocean currents and the
vertical movement of water.
Halocline = The rapid change in salinity close to the surface.
Pycnocline = The rapid change in density close to the surface.
Temperature
High levels of energy are required to heat water (high specific heat capacity) but it retains
warmth very efficiently. This means fluctuations in temperature are much less significant
than on land. Water temperature decreases with depth.
Thermocline = The rapid change in temperature close to the surface.
The global distribution of warm and cold surface currents:
Surface currents = Surface circulation – make up about 10% of ocean water and form in the
upper 400m.
Deep water currents = Thermohaline circulation – 90% of oceans and are driven by density
and gravity.
Influenced by solar heating, winds, gravity and the Coriolis effect.
Ocean conveyor belt:
• Ocean circulation regulates climate as oceans respond at a slower rate.
• Water has a very high specific heat capacity and stores 50% solar insolation.
Absorption and sea-surface temps highest at the equator.
• Surface currents transport warm water poleward but tend not to mix with cold deep
water.
• The Coriolis effect (left deflection of wind due to Earth’s spin) causes surface winds
and currents to rotate anticlockwise in the southern hemisphere and clockwise in
the northern hemisphere.
• At polar regions surface currents become cooler, more saline and denser.
• Water sinks to ocean depths and starts to disperse horizontally as deep-water
currents called thermohaline circulation which flows back to the equator.
The pattern of circulation in the North Atlantic
Gulf stream = relatively warm, saline water flows off the coast of Florida northeast. Heat
energy transferred to mid latitudes of western Europe.
North Atlantic Drift = moves from the Norwegian coast into the Arctic. Water cools and
sinks to form deep-water currents which will surface at the equator in 150-250 years.
Labrador Current = Northwest Atlantic, flows south from the Arctic.
Mediterranean inflow = Warm and saline through the straights of Gibraltar and into the
Atlantic. Eventually density is matched, and mixing occurs.
Future – melting Arctic ice would decrease salinity which could reduce density sufficiently to
prevent water sinking in the North Atlantic. Disrupts the ocean conveyor belt and alters
climate/weather. Argo project uses free-drifting floats to monitor temp and salinity of upper
2000m of ocean.