Long-term atmospheric changes Flashcards
Carbon dioxide
- Carbon dioxide is an important ‘Greenhouse’ gas in Quaternary glaciations
- CO2 plays a role in the synchronisation of Northern and Southern Hemisphere glaciations
Why does atmospheric CO2 decline during a glaciation?
(1) Chemical weathering
– Greater land area in glacial conditions
– Solution of rocks by carbonic acid locks up CO2
– Possibly 50 – 100 ppmv drop in CO2 concentration
attributable to chemical weathering
Why does atmospheric CO2 decline during a glaciation?
(2) Changes in oceans
– (a) Temperature change
– (b) Productivity of the oceans
» Light
» Nutrients
Changes in glacial oceans
(a) Temperature
• Oceans hold x60 more CO2 than atmosphere
• They control CO2 exchange with the
atmosphere
• Glacial oceans store even more CO2
• ….because CO2 is more soluble in colder water
Changes in glacial oceans
(b) Productivity
- CO2 is used by plankton
- Plankton dies and rains to ocean bottom continually
- Plankton numbers increase in the glacial oceans drawing extra CO2 from the atmosphere
- What causes plankton productivity to increase?
Ocean productivity
Abundance of plankton is
usually limited by availability of :
(1) Light
(1) Light In a glacial period northern sea ice pushes plankton belts to S where sun is stronger increasing productivity
Ocean productivity
Abundance of plankton is
usually limited by availability of :
(2) Nutrients
• Iron is usually in very limited supply in oceans
• It is an important nutrient
• The supply of iron increases in glacial
oceans
The effect of extra dust in the glacial atmosphere
• Dust not only generates greater productivity in the
oceans it also leads to:-
- Greater cloudiness = greater albedo
- consequent estimated cooling of 1oC
Dust in the atmosphere
• Dust is a source of condensation
nuclei
• The nuclei are important for cloud development
(if air humidity allows this)
Water vapour in the atmosphere
- Normally super abundant in interglacial phases
- Very effective greenhouse gas
- Exchange with the oceans is very important
Level of water vapour greatly reduced because:
– cold air holds less vapour
– restricted evaporation from cold oceans
– sea ice formation prevents evaporation
The importance of water vapour in glaciation
• Ocean still quite warm during glacial build-up
• Only later does moisture starvation affect growth of ice
sheets
• Reduced water vapour is not likely to be an initiator of global cooling
The Holocene began
11,700 calendar years ago
The Ipswichian Interglacial occurred in Oxygen Isotope Stage
5e
The Quaternary is
2.6 million years old
In the late Quaternary ice ages have occurred with a pacing of approximately
100,000 years
The eccentricity of the earth’s orbit is
the circularity of the orbit
Ocean current upwelling predominantly occurs
In the Indian and North Pacific Oceans
Orbital variations consist of:-
- Eccentricity - c. 100 k yrs (circularity)
- Obliquity - c. 42 k yrs (tilt of axis)
- Precession - c. 21 k yrs (‘wobble of axis)
Eccentricity is the weakest effect yet the ice
ages occur every
100,000 years
At present the northern hemisphere mid winter occurs
at perihelion
Perihelion is the point in the orbit when the Earth is
closest to the sun
The positions of the seasons on the Earth’s orbit will be reversed after
10,500 years
Summer solstice =
Hemisphere tilted directly
towards sun…produces longest day of year
Equinox =
direction of axis side on to sun
Aphelion =
Earth at most distant part of elliptical orbit
Perihelion =
Earth closest to sun
Increased algal blooms occur in the world’s oceans during glacial stages because
increased levels of iron enter the oceans, supplying a key nutrient
In the last 800,000 years, CO2 typically peaks
at the start of an interglacial
Eustatic sea level relates to
Global sea level change
