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Ocean Currents

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Title: Ocean Currents


1
Ocean Currents
  • http//oceanworld.tamu.edu/students/currents/index
    .html
  • Ocean World

2
What is a current?
3
Ocean currents
  • a steady horizontal movement of water or air in a
    definite direction.
  • Ocean currents flow in complex patterns affected
    by wind, the water's salinity and heat content,
    bottom topography, and the Earth's rotation

4
Topography of the ocean. Red and yellow hills
blue valleys
5
Ocean currents
  • Surface currents
  • Upper kilometer wind driven
  • Deeper Currents gravity driven
  • Mixing moves very cold dense water up to the
    surface. The dense water is replaced by cold
    dense water that sinks to the bottom near
    Greenland, Norway and Antarctica. Deeper water is
    affected by long variability of climate.

6
Wind
  • Wind-driven currents affect about 20 of the
    ocean's total volume. These are the only currents
    that most people see. Sailors have charted
    patterns of the ocean's currents for hundreds of
    years.
  • The sun ultimately creates winds in the
    atmosphere and ocean currents. Because the
    equator receives more direct rays from the sun
    throughout the year, this creates a temperature
    imbalance. Unequal heating of the atmosphere on
    land and the oceans creates winds and
    circulation.

7
Wind energy is converted to water movements
called "currents" by friction between the wind
and the water surface. The surface currents
resemble the surface winds. Once these surface
currents are set in motion they are influenced by
three other factors Coriolis effect, presence of
coasts, and horizontal pressure gradients.
8
Ekman spiral The Ekman transport combined with
the Coriolis force causes each layer of water to
change angle slightly creating a spiraling affect
in the water the spiraling is clockwise in the
northern hemisphere and counter-clockwise in the
southern hemisphere
9
Gyres
10
Trade winds
  • originally named by sailors, the trade-winds are
    a group of winds which blow from the east.
  • The trade-winds are part of the Hadley cells
    which lie between 30 degrees North and 30 degrees
    South. The easterly trade-winds are the surface
    component of Hadley cells which due to the
    Coriolis effect move from the Northeast north of
    the Equator and from the Southeast south of the
    equator.
  • Where the two sets of winds meet along the
    Equator the lack of persistent winds result in
    relative calm seas, this area is known by sailors
    as the doldrums. Air masses that move from
    subtropical high pressure belts toward the
    equator. They are northeasterly in the Northern
    Hemisphere and southesterly in the Southern
    Hemisphere

11
Salinity
  • a measure of the quantity of dissolved salts in
    ocean water.
  • This is influenced by the geologic formations
    underlying the area.
  • Salinity is lower in areas underlain by igneous
    formations and higher in areas underlain by
    sedimentary formations.
  • Higher salt concentrations are also more likely
    in arid regions where water evaporates leaving
    the same amount of salt in less water and thus
    increasing the salinity.

12
Density
  • the average mass per unit volume a measure of
    how much matter is squeezed into a given space
  • the more closely packed the molecules, the higher
    the density of the material.
  • Density in the ocean is determined by salinity
    and temperature

13
Deep Ocean circulation
  • the slow circulation of water at great depths is
    driven by density differences rather than by wind
    energy

14
Upwelling
  • a current of cold, nutrient-rich water rising to
    the surface.
  • Upwellings are caused by strong seasonal winds
    moving surface coastal water out from the coast
    and leaving a space that the upwelling fills in.
  • Many marine plants and animals live off this
    nutrient-rich water.

15
Great Ocean conveyor belt
16
The Global Conveyor Belt
  • The global conveyor belt thermohaline circulation
    is driven primarily by the formation and sinking
    of deep water (from around 1500 meters to the
    Antarctic bottom water overlying the bottom of
    the ocean) in the Norwegian Sea.
  • This circulation is thought to be responsible for
    the large flow of upper ocean water from the
    tropical Pacific to the Indian Ocean
  • UNEP http//www.grida.no/climate/vital/32.htm

17
Sea level changes
  • Over the last 100 years, the global sea level has
    risen by about 10 to 25 cm.
  • It is likely that much of the rise in sea level
    has been related to the concurrent rise in global
    temperature over the last 100 years.
  • On this time scale, the warming and thermal
    expansion of the oceans may account for about 2-7
    cm of the observed sea level rise, while the
    observed retreat of glaciers and ice caps may
    account for about 2-5 cm..

18
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