IB Environmental systems and societies Topic 4.1D Stratification Revision Notes (HL)

IB Environmental systems and societies Topic 4.1D Stratification Revision Notes (HL) | RevisionDojo

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Stratification: density differences lock water bodies into stable layers that resist mixing

Definition

Stratification

Stratification is a common phenomenon in aquatic ecosystems, where water forms distinct layers due to differences in temperature and density.

In most lakes and oceans temperature falls with depth, so warm, less dense water sits above colder, denser water.
This density difference produces stratification, distinct layers that resist vertical mixing.
Because layers stay separate, stratification controls the distribution of oxygen, nutrients, and organisms, shaping productivity and stability.
The cause is water's maximum density at 4°C: water above or below 4°C is less dense, so it floats (covered fully in 4.1B).

The three thermal layers of a deep lake

Epilimnion: the warm, wind-mixed surface layer, rich in oxygen from air exchange and photosynthesis, where phytoplankton grow.
Metalimnion (thermocline): the transition zone where temperature drops rapidly, forming a barrier that blocks the exchange of oxygen and nutrients between layers.
Hypolimnion: the cold, dark, dense bottom layer where decomposition dominates, so oxygen is low but decomposition-released nutrients are high.

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IB Environmental systems and societies 4.1D Stratification Notes

Stratification: density differences lock water bodies into stable layers that resist mixing

The three thermal layers of a deep lake

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Stratification: density differences lock water bodies into stable layers that resist mixing

The three thermal layers of a deep lake

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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 4.1D Stratification 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

Stratification: density differences lock water bodies into stable layers that resist mixing

The three thermal layers of a deep lake

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Stratification: density differences lock water bodies into stable layers that resist mixing

The three thermal layers of a deep lake

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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