Atmosphere 3 - Case-Study from Earth’s past: Insolation control of Monsoons Flashcards
Who was Henrich Barth?
a German explorer who was the first European to witness cave art in the Sahara
What does the Sahara cave art depict?
state of life depicted is very different the the present ecosystem
What are the 2 hypothesis for how the cave art is depicted in the Sahara?
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
How is a wet summer monsoon generated in the Sahara?
strong summer heating, creates low pressure over N Africa drawing moisture from tropical Atlantic
How do dry trade winds inhibit precipitation in N Africa?
Winter cooling creates high pressure
in northwest Sahara Desert enhancing
flow of the northern trade winds
Where does most rainfall in N Africa come from?
summer monsoon
What is an example of how vegetation patterns are driven by summer monsoon patterns?
Rainforest near equator
Desert scrub in the Sahara
How can orbital cycles be linked to monsoons?
Monsoons are linked with the strength of insolation on orbital time scales
When was the last green Sahara?
started 14 Ka ago and ended 5 Ka ago
What lakes were present in the Sahara?
Many small lakes in the western Sahara in Central Sahara there was the Megalake chad
Complex river system and alluvial outwash plains
What is palaeo-limnology? (evidence for orbital scale changes)
drilling ancient lake sites
What is happening to the Sahara that is removing the geological record?
lake sediment has dried and turned to dust which gets blown away by strong seasonal winds (dust storms in UK)
What are diatoms?
single-celled algae
What do diatoms live in and why is this the case?
“houses of glass” as their shells are made of opaline silica which has a glassy texture
Why is the silica shell of diatoms so important for predicting past climates?
the silica glass is very resistant so does not break down easily
How much of the air we breath is produced by diatoms?
20-30%
How do diatoms form a fundamental part of the food chain?
they are in the first trophic level so are a primary producer
produce long-chain fatty acids
How many species are there though to be of diatoms?
20,000 to 2 million (making them one of the most diverse protists on earth)
How can diatoms tell us about the health of aquatic eocsystems?
Specific diatoms will only live in specific conditions
How can diatoms specificity help reconstruct paleoclimate?
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
How might have green Sahara phases have helped in hominin evolution?
Hundred of generations of hominins could have thrived in each green Sahara phase
What would have happened to hominin populations with green Sahara phase termintion?
major population collapses and
displacements, and habitat fragmentation with associated potential for isolating
small residual populations (allowing genetic drift and natural selection)
