Upwelling,
Down welling,
and Current Types
I. Ekman Transport
A. Definition – term given for the 90
degree net transport of the surface layer
due to wind forces and Coriolis Effect.
B. First investigated in 1902 by
Vagn Walfrid Ekman
C. Ekman motion theory
1. In the northern hemisphere this
transport is at a 90 degree angle to the
right of the direction of the wind.
2. In the southern hemisphere it occurs
at a 90 degree angle to the left of the
direction of the wind.
D. Ekman Spiral – Model plotting the water
layers at various directions, speed
and depth
Ekman Spiral Model
II. Upwelling
A. Definition – upward movement of the
deeper, cooler waters toward the
surface pushing surface waters away
from the shore due to the Ekman
Transport.
B. Description
1. Coriolis Effect moves water at right
angles slightly right of the
direction the wind is blowing
resulting in surface currents
pushing the surface waters offshore.
2. When surface waters are pushed
offshore, water from below is drawn
upward to replace them.
C. Caused by Waters Diverging away from
a region.
D. Effects
1. Brings nutrient –rich waters to the
surface encouraging seaweed and
phytoplankton growth.
2. Moves drifting larvae long distances
from their natural habitat affecting
population stability.
III. Downwelling
A. Definition – Surface waters move
toward the shore due to Ekman
Transport and sink to the bottom.
B. Remember: water is a fluid in constant
motion; a change in the distribution of
water in one area is accompanied by
a compensating change in another
area.
C. Caused by a Waters Converging toward
a region.
Upwelling and Downwelling
Diagram
IV. Types of Currents
1. Gravitational Currents- the vertical pull of
gravity and the buoyant force on a mass of
fluid
2. Surface Currents- caused by movement of
a fluid due to a transfer of energy from
another source such as wind
3. Thermohaline Circulation- the movement of
a fluid due to differences in salinity or
temperature
B. Types of Currents (continued)
4. Haline Currents- the movement of a
fluid due to differences in salinity.
5. Convection Currents- the movement
of a fluid due to differences in
temperature