Long-term atmospheric changes

Question 1

Carbon dioxide

Answer 1

• Carbon dioxide is an important ‘Greenhouse’ gas in Quaternary glaciations
• CO2 plays a role in the synchronisation of Northern and Southern Hemisphere glaciations

Question 2

Why does atmospheric CO2 decline during a glaciation?

(1) Chemical weathering

Answer 2

– 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

Question 3

Why does atmospheric CO2 decline during a glaciation?

(2) Changes in oceans

Answer 3

– (a) Temperature change
– (b) Productivity of the oceans
» Light
» Nutrients

Question 4

Changes in glacial oceans

(a) Temperature

Answer 4

• 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

Question 5

Changes in glacial oceans

(b) Productivity

Answer 5

• 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?

Question 6

Ocean productivity

Abundance of plankton is
usually limited by availability of :

(1) Light

Answer 6

(1) Light
In a glacial period northern sea
ice pushes plankton belts to S
where sun is stronger
increasing productivity

Question 7

Ocean productivity

Abundance of plankton is
usually limited by availability of :

(2) Nutrients

Answer 7

• Iron is usually in very limited supply in oceans
• It is an important nutrient
• The supply of iron increases in glacial
oceans

Question 8

The effect of extra dust in the glacial atmosphere

Answer 8

• Dust not only generates greater productivity in the
oceans it also leads to:-
- Greater cloudiness = greater albedo
- consequent estimated cooling of 1oC

Question 9

Dust in the atmosphere

Answer 9

• Dust is a source of condensation
nuclei
• The nuclei are important for cloud development
(if air humidity allows this)

Question 10

Water vapour in the atmosphere

Answer 10

• Normally super abundant in interglacial phases
• Very effective greenhouse gas
• Exchange with the oceans is very important

Question 11

Level of water vapour greatly reduced because:

Answer 11

– cold air holds less vapour
– restricted evaporation from cold oceans
– sea ice formation prevents evaporation

Question 12

The importance of water vapour in glaciation

Answer 12

• 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

Question 13

The Holocene began

Answer 13

11,700 calendar years ago

Question 14

The Ipswichian Interglacial occurred in Oxygen Isotope Stage

Answer 14

5e

Question 15

The Quaternary is

Answer 15

2.6 million years old

Question 16

In the late Quaternary ice ages have occurred with a pacing of approximately

Answer 16

100,000 years

Question 17

The eccentricity of the earth’s orbit is

Answer 17

the circularity of the orbit

Question 18

Ocean current upwelling predominantly occurs

Answer 18

In the Indian and North Pacific Oceans

Question 19

Orbital variations consist of:-

Answer 19

• Eccentricity - c. 100 k yrs (circularity)
• Obliquity - c. 42 k yrs (tilt of axis)
• Precession - c. 21 k yrs (‘wobble of axis)

Question 20

Eccentricity is the weakest effect yet the ice

ages occur every

Answer 20

100,000 years

Question 21

At present the northern hemisphere mid winter occurs

Answer 21

at perihelion

Question 22

Perihelion is the point in the orbit when the Earth is

Answer 22

closest to the sun

Question 23

The positions of the seasons on the Earth’s orbit will be reversed after

Answer 23

10,500 years

Question 24

Summer solstice =

Answer 24

Hemisphere tilted directly

towards sun…produces longest day of year

Question 25

Equinox =

Answer 25

direction of axis side on to sun

Question 26

Aphelion =

Answer 26

Earth at most distant part of elliptical orbit

Question 27

Perihelion =

Answer 27

Earth closest to sun

Question 28

Increased algal blooms occur in the world’s oceans during glacial stages because

Answer 28

increased levels of iron enter the oceans, supplying a key nutrient

Question 29

In the last 800,000 years, CO2 typically peaks

Answer 29

at the start of an interglacial

Question 30

Eustatic sea level relates to

Answer 30

Global sea level change