Thermohaline Circulation

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Ocean Thermohaline Circulation Deep Ocean
Currents
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Thermohaline Circulation

• Thermohaline Circulation (THC)
• refers to the part of the large-scale ocean
  circulation that is driven by global density
  gradients created by variations temperature and
  salinity.

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Vertical Variation in the Ocean

• Density varies with
• Temperature (Warm water is less dense than cold
  water)
• Salinity (Salty water is denser than fresh water)
• Pressure (High pressure also increases the
  waters density)

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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.

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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?
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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!

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Halocline
What is happening to the salinity as you move
from the surface zone to the deep zone?
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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.

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• These clines are Gradients
• The thermocline the depth range with large
  temperature gradient.
• The haloclinethe 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.

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Thermohaline CirculationHow 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.

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• 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

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The Day After Tomorrow depicts what might
happen if the Thermohaline Circulation in the
North Atlantic were to suddenly switch off.
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Animation

• Animation http//www.youtube.com/watch?v3niR_-Kv
  4SM

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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