Quiz 5

Question 1

General Circulation of the atmosphere

Answer 1

Intertropical convergence zone (ITCZ)
Trade winds
Subtropical highs
Westerlies
Polar front (Subpolar lows)
Polar easterlies
Polar highs

Question 2

What is the Monsoonal Circulation?

Answer 2

• In summer, air moves upward over the land and downward over the ocean
• Upward movement creates low pressure above land
• Downward movement creates high pressure above ocean
• Precipitation is heaviest in regions with low pressure and upward air motion

Question 3

What are examples of today’s monsoon areas around the world?

Answer 3

They consist of those in South Asia, Southeast Asia, parts of West Africa which are very weak. The only monsoon systems in the Southern Hemisphere are the Amazon Valley and NE Australia.

Question 4

Monsoons on pangea ~200 myA

Answer 4

“Supermonsoons” due to strong heating in the summer and strong cooling in winter

Question 5

Earth’s axis tilt change (obliquity)

Answer 5

• In 41,000-year cycle, larger tilt (closer to 24.5°) produces more insolation at both poles in their respective summers
• ~10,000 years ago earth’s tilt was at its maximum
• Each hemisphere had warmer summers, colder winters
• Today, both hemispheres experience smaller seasonal amplitudes

Question 6

What is the Precession of the Equinoxes: Insolation Control of Seasonal Variations?

Answer 6

It explains how one full orbit around the Sun is completed in 23,000 years and gives a prediction that in 11,500 years from today June and December solstices will be in exactly opposite positions on the orbit.

Question 7

What is the evidence of the June 21 solstice position occurring near the aphelion (most distant pass)?

Answer 7

There is reduced radiation during our summer.

Question 8

11,500 years ago situation was reverse, what happened during that time?

Answer 8

There was increased radiation during the Northern Hemisphere summer (perihelion position); decreased radiation during the Northern Hemisphere winter and greater temperature differences between winter and summer occurred 11.5K years ago.

Question 9

What is the Orbital Monsoon Theory?

Answer 9

• greater summer radiation intensifies the wet summer monsoon
• decreased winter radiation intensifies the dry winter monsoon
• Monsoonal strength is modified by a 23,000-year precessional cycle

Question 10

Evidence form the North African Summer Monsoon ~11K years ago, What was the sapropel accumulation in the Mediterranean Sea?

Answer 10

The evidence points deep water is oxygen-rich (sinking of saltier water to the bottom) in which deposits were found on the sea floor dated 10,000-8,000 years old.

Question 11

What is saporel?

Answer 11

They are organic carbon-rich deposits formed in anoxic conditions.

Question 12

When are the sapropel layers best developed?

Answer 12

They are best developed near the time of the strongest summer insolation (last time ~11,000 years ago). Earlier sapropel layers occur at regular 23,000-year intervals

Question 13

What are examples of glaciers?

Answer 13

Continental ice sheets (now only in Greenland and Antarctica), and mountain (alpine) glaciers

Question 14

How do glaciers form?

Answer 14

They form by compaction of snow; transformation into firn, and finally into glacial ice along with accumulation and ablation.

Question 15

The fastest moving ice is at the surface why is that?

Answer 15

• It is due to the central portions of large ice sheets which form high central domes
• ice streams down the flanks which forms ice lobes, ice shelves over shallow ocean
• icebergs occasionally break off and float away.

Question 16

What controls the size of ice sheets?

Answer 16

• Through accumulation in which they initially as snow at mean annual temps below 10°C
• melting begins at mean summer temps above 0°C (= mean annual temps above -10°C).

Question 17

What is ice mass balance?

Answer 17

It is net balance between accumulation and ablation.

Question 18

What is the equilibrium line?

Answer 18

The boundary between positive and negative mass balance.

Question 19

What is The Milankovitch Theory?

Answer 19

• summer insolation controls ice sheet growth
• ice sheet growth in the Northern Hemisphere which occurs during times when summer insolation is reduced
• the amount of summer insolation arriving at the top of atmosphere at 65°N can vary by +/-12% around the long-term mean value

Question 20

In perfect ice sheet growth conditions, when does Low summer insolation occur?

Answer 20

When:

• the earth’s orbital tilt is small
• the northern summer solstice occurs once the earth is farthest from the sun
• orbit is highly eccentric

Question 21

What else happens in a low summer insolation?

Answer 21

Decrease in tilt results in diminishing seasonal amplitude such as warmer winters, colder summers. The June 21 solstice position starts to occur near the aphelion (most distant pass) which causes a reduction in radiation during Northern Hemisphere summer and 11,500 years ago (and ~ 11,000 years from now) there will be increased radiation during the Northern Hemisphere summer (perihelion position).

Question 22

Tops of ice sheets can reach elevations of 2-3 km where temps are cooler
What is the average lapse rate of cooling?

Answer 22

The feedback effect weakens when ice sheets reach high elevations

Question 23

Annual accumulation rate is ~ 0.3 meters of ice

How long will it take a full-sized glacier to grow up to 3,000 meters thick?

Answer 23

Around 10,000 years

Question 24

Ice sheets lag behind insolation max & MIN

Answer 24

• Water has a high heat capacity and reacts slowly to changes to heat applied to it
• Similarly, ice sheet rates of growth and ablation react slowly to radiation increase or decrease
• Theoretically, the phase lag between the orbital and ice sheet cycles is ¼ wavelength

Question 25

Is the Milankovitch Theory a Full Answer?

Answer 25

It explains the ice volumes at 41K and 23K-year cycles. It also explains the time lag behind summer insolation maxima. However, it does not explain the dominance of 41K-year cycle over 23K-year cycle over the interval of 2 million years in the Northern Hemisphere. It also fails to explain the emergence of a 100K-year oscillation in the last 0.9 million years

Question 26

What are examples of how you would use ice cores as the climate data?

Answer 26

• Oldest cores in an ice sheet taken at the top of ice domes

- air circulates in the upper part of unconsolidated ice dome

Question 27

What are examples of Orbital-Scale CO2 Changes?

Answer 27

• 800,000-year record from Dome C in Antarctica
• Large-scale 100,000-year cycles similar to the ice volume cycles determined by the marine O18/O16 isotope analysis
• Variations of CO2 between ~200 ppm during glaciations and ~300 ppm in the interglacials

Question 28

What are examples of tectonic-scale carbon transfers?

Answer 28

• Chemical weathering (hydrolysis) removes CO2 from the atmosphere
• carbon stored in shells and buried on the ocean floor
• subduction which carries carbon down to the mantle
• volcanism which is the main source of CO2 in the atmosphere

Question 29

Carbon Isotope Analysis

Answer 29

• C12 isotope accounts for 99% of all carbon on Earth
• photosynthesis converts inorganic carbon to organic form
• plants incorporate C12 in their tissue more easily than C13 in the process of carbon isotope fractionation
• values of δO13 range from +2‰ in surface water (inorganic carbon) to -28 ‰ in terrestrial biomass (C12-enriched).

Question 30

What are examples of orbital-scale carbon transfers?

Answer 30

Ocean plankton converts inorganic carbon from seawater to organic carbon
shells of marine foraminifera CaCO3 are formed from inorganic carbon dissolved in seawater
- decrease in glacial carbon was due to the expansion of ice sheets and natural deforestation due to cooling of climate
- over 1,000 billion tons of carbon added to the deep ocean.

Question 31

What happened during the glacial transfers of carbon and oxygen?

Answer 31

• During glaciations, C12-enriched organic matter transferred to deep ocean
• O16-enriched water is extracted from the ocean to form glaciers
• Opposite transfers of C12 and O16 occur during interglacials: increase of terrestrial biomass and melt-water returning to the ocean

Question 32

How did carbon get into the deep ocean: increased co2 solubility in sea water

Answer 32

• Increased solubility of CO2 in colder seawater

- Atmospheric CO2 decreased by ~20-30 ppm when the deep ocean cooled by 2-3ºC during the LGM

Question 33

How did carbon get into the deep ocean: biological transfer from surface water

Answer 33

• Photosynthesis in the surface layer
• Organic tissue sinks to the seafloor
• Oxidation of organic matter to nutrient form

Question 34

biological transfer from surface water

Answer 34

• Today, most productive zones in the ocean are the areas of equatorial upwelling, coastal areas, and high-latitude oceans
• Lower productivity in central ocean gyres

Question 35

What is the carbon pump?

Answer 35

export of carbon due to higher productivity of plant plankton

Question 36

Iron fertilization hypothesis

Answer 36

iron delivered from the continents by stronger glacial winds

Question 37

What is the origin of the Orbital-Scale Changes in Methane?

Answer 37

• methane CH4 originated in wetlands, in anoxic (reducing) conditions
• wetland sources in the tropics such as swamps regulated by the summer monsoons
• bogs in subarctic regions expand during wet monsoon maxima and shrink during monsoon minima following the 23,000-year precession cycle.

Question 38

What does an 800,000-year record of atmospheric CH4 from Dome C, Antarctica show?

Answer 38

A presence of strong 23,000-year CH4 variations which can be explained by the control of tropical wetlands by summer monsoon rainfall along with the control of emissions from subarctic wetlands by midsummer warmth driven by insulation heating.

Question 39

Prior to 350 MYA, why is the 41,000-year cycle considered to be more obvious?

Answer 39

It is because the climate changes in the Arctic regions are more influenced by the tilt.

Question 40

What happened In the last 150,000 years?

Answer 40

There was phasing of the GHG relative to ice volume at the orbital period, forcing of the ice sheets at the 23K-year period (CH4), and finally an ice-driven feedback at the 41K-year period (CO2).