IB Environmental systems and societies Topic 4.1E Thermohaline Circulation Revision Notes (HL)

IB Environmental systems and societies Topic 4.1E Thermohaline Circulation Revision Notes (HL) | RevisionDojo

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Ocean upwelling and thermohaline circulation: wind and density move water, nutrients and heat around the planet

Definition

Upwelling

Upwelling refers to the vertical movement of deep, cold, nutrient-rich water to the surface due to the displacement of surface waters by wind.

Upwelling is the rise of cold, dense, nutrient-rich water from depth to the surface when wind pushes surface water away.
The rising water carries nitrates, phosphates and silicates that fuel phytoplankton growth at the base of the food web.
Upwelling zones are among the most productive ecosystems on Earth, supplying roughly 25% of the global fish catch from about 5% of the ocean surface.

What drives coastal upwelling

Wind-driven surface flow: winds blowing parallel to a coast push surface water offshore, so deep water rises to replace it.
Coriolis effect: Earth's rotation deflects the moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Ekman transport: combining wind and Coriolis deflection, the net movement of the surface layer is about 90° to the wind direction, driving water away from the coast.
Seasonal and lake turnover: in stratified lakes, seasonal winds and cooling break stratification so cold, nutrient-rich bottom water rises.

Coastal upwelling is strongest along western continental margins, such as the Peru (Humboldt) and Benguela systems.

Why upwelling matters

Nutrients drive phytoplankton blooms that feed zooplankton, small fish, and top predators such as tuna, seabirds and whales.

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IB Environmental systems and societies 4.1E Thermohaline Circulation Notes

Ocean upwelling and thermohaline circulation: wind and density move water, nutrients and heat around the planet

What drives coastal upwelling

Why upwelling matters

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Ocean upwelling and thermohaline circulation: wind and density move water, nutrients and heat around the planet

What drives coastal upwelling

Why upwelling matters

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Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

IB Environmental systems and societies 4.1E Thermohaline Circulation Notes

Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

Ocean upwelling and thermohaline circulation: wind and density move water, nutrients and heat around the planet

What drives coastal upwelling

Why upwelling matters

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Ocean upwelling and thermohaline circulation: wind and density move water, nutrients and heat around the planet

What drives coastal upwelling

Why upwelling matters

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