Ocean Thermohaline Circulation
Deep Ocean Currents
Thermohaline Circulation
Thermohaline Circulation (THC)
• refers to the part of the largescale ocean circulation that is
driven by global density gradients
created by variations temperature
and salinity.
Vertical Variation in the Ocean
Density varies with:
1. Temperature (Warm water is less dense
than cold water)
2. Salinity (Salty water is denser than fresh
water)
3. Pressure (High pressure also increases the
water’s density)
How does temperature of
sea water vary with depth?
• Mixed Layer (surface layer)
– water in this area is mixed by
wind, temperature is steady.
•Thermocline (below mixed layer)
– temperature changes rapidly
with depth (cooling).
•Deep water layer
– Coolest layer, begins once
temperatures become steady
again.
Vertical Temperature Variation in the Ocean
What is happening
to the temperature
of the water as
you move from the
surface zone to
the deep zone?
Halocline
• Related to salinity (salt content) in
water.
• Salinity content increases with depth
• Halocline is a region where the salinity
changes most drastically within a narrow
range of depth
– Same as thermocline but related to salt
content instead of temperature!
Halocline
What is happening
to the salinity as
you move from the
surface zone to
the deep zone?
Pycnocline
• Related to the density of water.
• Density increases with depth.
• Pycnocline is a region where the density
changes most drastically within a narrow
range of depth.
– Same as thermocline but for density.
These “clines” are Gradients
•
The thermocline: the depth range with large temperature
gradient.
•
The halocline:the depth range with large salinity gradient.
•
The pycnocline: the depth range with large density
gradient.
•
can be more than one in the water column.
•
usually thermocline, halocline and pycnocline are at the
same depth range.
Thermohaline Circulation
How does it work?
• The temperature and salinity of ocean
water help drive deep ocean currents.
• When water cools, it is able to “hold” more
salt – becomes more dense and sinks,
allowing ‘warm’ water to float above it.
• The cooling of water and the increasing of
salinity are the driving forces of
thermohaline circulation.
• Deep ocean currents navigate the oceans.
When they reach warmer areas (low
latitudes), the water warms and rises to
the surface. Allows for upwelling of
nutrients.
• The water now moves along the surface in
warm currents until it reaches high
latitudes where it will cool, become more
dense and sink.
• The process continues and forms the
“Global Conveyer Belt”
‘The Day After Tomorrow’ depicts what might
happen if the Thermohaline Circulation in the
North Atlantic were to suddenly switch off.
Animation
• Animation:
http://www.youtube.com/watch?v=3niR_Kv4SM
Your Task
• Complete the formative questions,
assessing your understanding of
thermoclines, haloclines, pycnoclines, and
how thermohaline circulation works.
• Show me before moving on.
• Complete Thermocline Lab Assignment