Upwelling in the World Ocean

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Upwelling in the World Ocean
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Presentation Points

• Mechanisms that create ocean upwelling
• Types of upwelling
• Identifying upwelling on satellite-derived maps
• Ecological and economic effects of upwelling

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Mechanisms that create ocean upwelling

• Wind
• Coriolis Effect
• Ekman Transport

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Upwelling refers to deep water that is brought to
the surface.
Areas of upwelling are created by surface winds
that pull water away from an area. This deficit
of water on the surface invites water to come up
from deeper regions.
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To understand upwelling, you must be familiar
with how the Coriolis Force affects ocean surface
currents. The Coriolis Effect acts on moving
water, because it is not attached to the rotating
Earth. As water flows over the rotating earth,
it appears to deflect to the right in the
Northern Hemisphere and the left in the Southern.
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Due to friction between the layers of water in
the ocean and the Coriolis Effect, the net result
of wind blowing across the surface of the water
is transportation of a layer of water 90 degrees
to the direction of the wind. This is known as
Ekman Transport.
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Types of Upwelling

• Equatorial
• Coastal
• Seasonal

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1. Equatorial Upwelling
Water Flow
Upwelling
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Look at the equator in the Pacific Ocean.
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2. Coastal Upwelling (follow the black arrows)
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Whats the difference between Peru(A) and
Columbia (B)?
B
A
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3. Seasonal upwelling
Wind
Wind
Onshore winds pile water up on shore, thus
surface water will be forced downward. This is
downwelling.
Offshore winds take water away from shore, thus
water from depth will upwell to the surface.
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The Monsoonal wind shifts in Oman create very
different conditions.
Wind
Wind
April, 1999 Onshore winds Downwelling
August, 1999 Offshore winds Upwelling
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Identifying upwelling on satellite-derived maps

• Sea Surface Temperature
• Ocean Color

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The deep water that surfaces in upwelling is
cold by looking at Sea Surface Temperature maps
we can identify cool upwelled water versus hotter
surface water.
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Upwelled water also contains nutrients (nitrate,
phosphate, silicate) and dissolved gases (oxygen
and carbon dioxide) that are not utilized at
depth because of a lack of sunlight.Now on the
surface, these nutrients and gases help to fuel
photosynthesis by small algae called
phytoplankton.
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Phytoplankton photosynthesize using specialized
color pigments called chlorophyll. Thus, Ocean
Color maps are another way to identify areas of
upwelling. Where on this ocean color map are
high phytoplankton concentrations?
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Ecological and Economic effects of upwelling

• Upwelling leads to more phytoplankton
• More phytoplankton leads to more fish
• More fish lead to commercial fishing jobs and to
  more seafood

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Phytoplankton come in many shapes and forms.
Collectively they form the base of oceanic food
webs.
Without upwelling many of the worlds fisheries
would not thrive.
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Some climatic events can reduce upwellings.

El Nino
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Along Perus coast, an El Nino event decreases
the coastal winds. Thus the upwelling from below
is slowed.
An El Nino condition results from weakened trade
winds in the western Pacific Ocean near
Indonesia, allowing piled-up warm water to flow
toward South America.
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Even though upwelling areas account for only 1
of the ocean surface, they support 50 of the
worlds fisheries.
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Productivity (phytoplankton growth) of an area
is determined by the rate and the duration of
upwelling.

• Rate of upwelling determines phytoplankton cell
  size.

• Duration of upwelling determines the total amount
  of phytoplankton.

small vs. large
few vs. many
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Classification of upwelling systems in terms of
rate and duration
After Thurman, H.V. (1994)
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• Moderate rates of upwelling for long duration (8
  months or longer) provide the ultimate
  combination for a large fishery.
• With too low or too high a rate, phytoplankton
  are small, so there is a trophic level between
  the algae and the fish.therefore the fish
  receive less energy.

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Upwelling and Fisheries
January
April
July
October
Using this series of Sea Surface Temperature Maps
from 1999, can you determine areas/times for
possible fisheries? (Hint Look at Perus coast
in January and April. Look at the northwestern
tip of Africa in July and October.)