Understanding Deep Ocean Circulation and Salinity Patterns

 
Deep Ocean Circulation
 
GEO101
Spring 2023
 
Contents
 
 Ocean Salinity
 The Vertical Structure of Oceans
 Deep-water Formation
 The Thermohaline Conveyor Belt
 Deep Ocean Currents and Climate
Ocean salinity
salinity = salt
  Ocean is 3.5% salt.
  extra density
concentrated in oceans:
  Precipitation dissolves salts.
  Rivers transport.
  Evaporation leaves the salt.
 
[31.5%]
 
Ocean salinity
 
oceans ever-saltier?
  early oceans less salty, but stable for
last 1.5 billion years
  input = outputs
 
 
Salt deposits
Biological uptake
(e.g., coral)
Salt spray
 
Ocean salinity
 
spatial variation
    salt inputs:
        rivers (e.g., Mediterranean & Nile)
    salt outputs:
        sediments or spray
    water loss minus gain:
        sea ice: ice crystals exclude salt
        evaporation – precipitation
 
 
 
Ocean Salinity
 
evaporation - precipitation
 
Ocean Salinity
 
Brinicle video
 
The Vertical Structure of Oceans
 
Ocean water varies vertically in terms of:
   temperature:
 
As you go deeper, temperature drops.
         Sun and atmosphere warmth
   salinity:
 
As you go deeper, salinity increases.
          salt inputs from river and rainfall
         deep ocean receives salt no freshwater
 
 
 
Vertical Structure of Oceans
 
water density:
    As you go deeper, density increases.
    Why?
      higher salinity
      pressure from overlying water
      lower temperature (note: freshwater
density peaks at 4°C)
 
 
 
Vertical Structure of Oceans
 
three general layers:
    surface layer: warm, mixed by wind
    transition zone:  rapid changes
    deep water: cold, salty, dense.
How do the three layers mix?
 
Deep-water Formation
 
surface water moved by wind
   Density and salinity change with latitudes.
      Evaporation increases salinity.
      Ice formation increases salinity.
      Cooling increases density.
   Cold, dense water sinks.
 
Deep-water formed as:
   North Atlantic Deep Water (NADW), off the coast of Greenland
   Antarctic Bottom Water (AABW), off Antarctica
 
The Thermohaline Conveyor Belt
 
Sinking water creates a “conveyor belt”.
“thermohaline” (temperature and salinity)
   After sinking, NADW travels south and joins AABW.
   Water upward in Indian Ocean and North Pacific Ocean
deep water:
   17 ft hr
-1
, residence time = 500 years
 
conveyor belt moves:
nutrients
water
 
 
 
the thermohaline “conveyor belt” circulation connecting the surface currents (dotted lines)
with deep-ocean currents (solid line).
 
 
 
 
 
Deep Ocean Currents and Climate
 
Deep ocean delivers cold water, thus
cools atmosphere.
Thermohaline circulation plays an
important role in the carbon cycle by
moving CO
2
-rich surface waters into the
ocean depths.
It could be slowed or stopped by inputs
of fresh water into the North Atlantic.
 
Deep Ocean Currents and Climate
 
Fresh water inputs could come from the sudden drainage of
large lakes formed by melting ice at the close of the last Ice Age.
The fresh water would decrease the density of the ocean water,
keeping the water from sinking.
Without sinking, circulation would stop.
This would interrupt the transfer of heat from equatorial regions
to the northern midlatitudes.
This mechanism could result in relatively rapid climatic change
and is one explanation for periodic cycles of warm and cold
temperatures since the melting of continental ice sheets about
12,000 years ago.
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Explore the intricate relationship between ocean salinity, vertical structure, and deep-water currents in this informative collection of images and explanations. Discover how salt inputs and outputs influence ocean salinity levels, and learn about the factors that contribute to the vertical variations in temperature, salinity, and density within the oceans. Gain insights into the mechanisms driving the complex patterns of deep ocean circulation and their impact on climate.


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  1. Deep Ocean Circulation GEO101 Spring 2023

  2. Contents Ocean Salinity The Vertical Structure of Oceans Deep-water Formation The Thermohaline Conveyor Belt Deep Ocean Currents and Climate

  3. Ocean salinity salinity = salt Ocean is 3.5% salt. extra density concentrated in oceans: Precipitation dissolves salts. Rivers transport. Evaporation leaves the salt. [31.5%]

  4. Ocean salinity oceans ever-saltier? early oceans less salty, but stable for last 1.5 billion years input = outputs

  5. Salt deposits Biological uptake (e.g., coral) Salt spray

  6. Ocean salinity spatial variation salt inputs: rivers (e.g., Mediterranean & Nile) salt outputs: sediments or spray water loss minus gain: sea ice: ice crystals exclude salt evaporation precipitation

  7. Ocean Salinity evaporation - precipitation

  8. Ocean Salinity Brinicle video

  9. The Vertical Structure of Oceans Ocean water varies vertically in terms of: temperature: As you go deeper, temperature drops. Sun and atmosphere warmth salinity: As you go deeper, salinity increases. salt inputs from river and rainfall deep ocean receives salt no freshwater

  10. Vertical Structure of Oceans water density: As you go deeper, density increases. Why? higher salinity pressure from overlying water lower temperature (note: freshwater density peaks at 4 C)

  11. Vertical Structure of Oceans three general layers: surface layer: warm, mixed by wind transition zone: rapid changes deep water: cold, salty, dense. How do the three layers mix?

  12. Deep-water Formation surface water moved by wind Density and salinity change with latitudes. Evaporation increases salinity. Ice formation increases salinity. Cooling increases density. Cold, dense water sinks. Deep-water formed as: North Atlantic Deep Water (NADW), off the coast of Greenland Antarctic Bottom Water (AABW), off Antarctica

  13. The Thermohaline Conveyor Belt Sinking water creates a conveyor belt . thermohaline (temperature and salinity) After sinking, NADW travels south and joins AABW. Water upward in Indian Ocean and North Pacific Ocean deep water: 17 ft hr-1, residence time = 500 years conveyor belt moves: nutrients water

  14. the thermohaline conveyor belt circulation connecting the surface currents (dotted lines) with deep-ocean currents (solid line).

  15. Deep Ocean Currents and Climate Deep ocean delivers cold water, thus cools atmosphere. Thermohaline circulation plays an important role in the carbon cycle by moving CO2-rich surface waters into the ocean depths. It could be slowed or stopped by inputs of fresh water into the North Atlantic.

  16. Deep Ocean Currents and Climate Fresh water inputs could come from the sudden drainage of large lakes formed by melting ice at the close of the last Ice Age. The fresh water would decrease the density of the ocean water, keeping the water from sinking. Without sinking, circulation would stop. This would interrupt the transfer of heat from equatorial regions to the northern midlatitudes. This mechanism could result in relatively rapid climatic change and is one explanation for periodic cycles of warm and cold temperatures since the melting of continental ice sheets about 12,000 years ago.

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