Atmosphere 3 - Case-Study from Earth’s past: Insolation control of Monsoons

Question 1

Who was Henrich Barth?

Answer 1

a German explorer who was the first European to witness cave art in the Sahara

Question 2

What does the Sahara cave art depict?

Answer 2

state of life depicted is very different the the present ecosystem

Question 3

What are the 2 hypothesis for how the cave art is depicted in the Sahara?

Answer 3

Travellers from fertile crescent showed what was in their civilisation (unlikely to travel so far)
These depict what the Saharan habitat was like in the past

Question 4

How is a wet summer monsoon generated in the Sahara?

Answer 4

strong summer heating, creates low pressure over N Africa drawing moisture from tropical Atlantic

Question 5

How do dry trade winds inhibit precipitation in N Africa?

Answer 5

Winter cooling creates high pressure
in northwest Sahara Desert enhancing
flow of the northern trade winds

Question 6

Where does most rainfall in N Africa come from?

Answer 6

summer monsoon

Question 7

What is an example of how vegetation patterns are driven by summer monsoon patterns?

Answer 7

Rainforest near equator
Desert scrub in the Sahara

Question 8

How can orbital cycles be linked to monsoons?

Answer 8

Monsoons are linked with the strength of insolation on orbital time scales

Question 9

When was the last green Sahara?

Answer 9

started 14 Ka ago and ended 5 Ka ago

Question 10

What lakes were present in the Sahara?

Answer 10

Many small lakes in the western Sahara in Central Sahara there was the Megalake chad
Complex river system and alluvial outwash plains

Question 11

What is palaeo-limnology? (evidence for orbital scale changes)

Answer 11

drilling ancient lake sites

Question 12

What is happening to the Sahara that is removing the geological record?

Answer 12

lake sediment has dried and turned to dust which gets blown away by strong seasonal winds (dust storms in UK)

Question 13

What are diatoms?

Answer 13

single-celled algae

Question 14

What do diatoms live in and why is this the case?

Answer 14

“houses of glass” as their shells are made of opaline silica which has a glassy texture

Question 15

Why is the silica shell of diatoms so important for predicting past climates?

Answer 15

the silica glass is very resistant so does not break down easily

Question 16

How much of the air we breath is produced by diatoms?

Answer 16

20-30%

Question 17

How do diatoms form a fundamental part of the food chain?

Answer 17

they are in the first trophic level so are a primary producer
produce long-chain fatty acids

Question 18

How many species are there though to be of diatoms?

Answer 18

20,000 to 2 million (making them one of the most diverse protists on earth)

Question 19

How can diatoms tell us about the health of aquatic eocsystems?

Answer 19

Specific diatoms will only live in specific conditions

Question 20

How can diatoms specificity help reconstruct paleoclimate?

Answer 20

as we know the conditions that certain ones can live in so if freshwater diatoms are found in ocean sediments off the coast of N Africa it shows freshwater lakes were present in the Sahara

Question 21

How might have green Sahara phases have helped in hominin evolution?

Answer 21

Hundred of generations of hominins could have thrived in each green Sahara phase

Question 22

What would have happened to hominin populations with green Sahara phase termintion?

Answer 22

major population collapses and
displacements, and habitat fragmentation with associated potential for isolating
small residual populations (allowing genetic drift and natural selection)