Upwelling in the World OceanUpwelling in the World Ocean

Presentation PointsPresentation Points

Mechanisms that create ocean upwellingTypes of upwellingIdentifying upwelling on satellite-derived

mapsEcological and economic effects of

upwelling

Mechanisms that create Mechanisms that create ocean upwellingocean upwelling

WindCoriolis EffectEkman Transport

Upwelling refers to deep water Upwelling refers to deep water that is brought to the surface.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.

To understand upwelling, you must be familiar with how To understand upwelling, you must be familiar with how the Coriolis Force affects ocean surface currents. The the Coriolis Force affects ocean surface currents. The Coriolis Effect acts on moving water, because it is not Coriolis Effect acts on moving water, because it is not attached to the rotating Earth. As water flows over the attached to the rotating Earth. As water flows over the

rotating earth, it appears to deflect to the right in the rotating earth, it appears to deflect to the right in the Northern Hemisphere and the left in the Southern.Northern Hemisphere and the left in the Southern.

Due to friction between the layers of water in the ocean Due to friction between the layers of water in the ocean and the Coriolis Effect, the net result of wind blowing and the Coriolis Effect, the net result of wind blowing across the surface of the water is transportation of a across the surface of the water is transportation of a

layer of water 90 degrees to the direction of the wind. layer of water 90 degrees to the direction of the wind. This is known as Ekman Transport.This is known as Ekman Transport.

Types of UpwellingTypes of Upwelling

EquatorialCoastalSeasonal

1. Equatorial Upwelling1. Equatorial Upwelling

Water Flow

Upwelling

Look at the equator in the Look at the equator in the Pacific Ocean.Pacific Ocean.

2. Coastal Upwelling 2. Coastal Upwelling (follow the black arrows)(follow the black arrows)

What’s the difference between What’s the difference between Peru(A) and Columbia (B)?Peru(A) and Columbia (B)?

B

A

3. Seasonal upwelling3. Seasonal upwelling

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.

Wind Wind

The Monsoonal wind shifts in The Monsoonal wind shifts in Oman create very different Oman create very different

conditions.conditions.

August, 1999Offshore winds: Upwelling

April, 1999Onshore winds: Downwelling

WindWind

Identifying upwelling on Identifying upwelling on satellite-derived mapssatellite-derived maps

Sea Surface TemperatureOcean Color

The deep water that surfaces in upwelling is The deep water that surfaces in upwelling is cold; by looking at Sea Surface Temperature cold; by looking at Sea Surface Temperature

maps we can identify cool upwelled water maps we can identify cool upwelled water versus hotter surface water.versus hotter surface water.

Upwelled water also contains nutrients Upwelled water also contains nutrients (nitrate, phosphate, silicate) and dissolved (nitrate, phosphate, silicate) and dissolved

gases (oxygen and carbon dioxide) that gases (oxygen and carbon dioxide) that are not utilized at depth because of a lack are not utilized at depth because of a lack

of sunlight.of sunlight.

Now on the surface, these nutrients and Now on the surface, these nutrients and gases help to fuel photosynthesis by gases help to fuel photosynthesis by

small algae called phytoplanktonsmall algae called phytoplankton..

Phytoplankton photosynthesize using Phytoplankton photosynthesize using specialized color pigments called chlorophyll. specialized color pigments called chlorophyll. Thus, “Ocean Color” maps are another way to Thus, “Ocean Color” maps are another way to

identify areas of upwelling. Where on this identify areas of upwelling. Where on this ocean color map are high phytoplankton ocean color map are high phytoplankton

concentrations?concentrations?

Ecological and Economic Ecological and Economic effects of upwelling: effects of upwelling:

Upwelling leads to more phytoplanktonMore phytoplankton leads to more fishMore fish lead to commercial fishing jobs

and to more seafood

Phytoplankton come in many shapes Phytoplankton come in many shapes and forms. Collectively they form the and forms. Collectively they form the

base of oceanic food webs.base of oceanic food webs.

Without upwelling many of the Without upwelling many of the world’s fisheries would not thrive.world’s fisheries would not thrive.

Some climatic events can reduce Some climatic events can reduce upwellings.upwellings.

El Nino

~

Along Peru’s coast, an El Nino event decreases Along Peru’s coast, an El Nino event decreases the coastal winds. Thus the upwelling from the coastal winds. Thus the upwelling from

below is slowed.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.

Even though upwelling areas Even though upwelling areas account for only 1% of the ocean account for only 1% of the ocean surface, they support 50% of the surface, they support 50% of the

worlds fisheries.worlds fisheries.

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.

few vs. manysmall vs. large

Classification of upwelling systems in terms of Classification of upwelling systems in terms of rate and duration:rate and duration:

After Thurman, H.V. (1994)

Low Medium HighRATE

DU

RA

TIO

N

Lon

g

S

hort

•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.

Upwelling and FisheriesUpwelling and Fisheries

Using this series of Sea Surface Temperature Maps from 1999, can you determine areas/times for possible fisheries?

(Hint: Look at Peru’s coast in January and April. Look at the northwestern tip of Africa in July and October.)

January April

July October