// lecture 22

Question 1

bubbles in ice cores

Answer 1

contain ancient air with the CO2 and CH4 of the time when the ice was formed.

Question 2

antarctic ice cores

Answer 2

800kyr record from antarctica

Question 3

land ice

Answer 3

• last glacial age - 20kbp
• disappearing ice - 12kbp
• present conditions - 0kbp

Question 4

the previous ice age (-20kbp)

Answer 4

sea level was 120 meters lower than now. possible to walk from siberia to alaska.

• ice volume in NH 15 times today’s.
• ice 2-3 km thick over much of north america. much more sea ice.
• global temp. about 6 C colder than today.
• CO2 about 180 ppm compared to 275 ppm in preindustrial era and 400 ppm now.
• windier and dustier than now.

Question 5

most of ice gone by 8000 bp

Answer 5

• laurentide ice sheet entirely covered canada and some northern states.
• lower sea level allowed for migrations across the bering strait.
• meltwater was trapped inland as the ice sheet retreated.
• the great lakes are the last vestige of this ice sheet.

Question 6

ice ages are

Answer 6

simultaneous in both hemispheres

Question 7

ice cores and ice ages:

Answer 7

• temperature, dust, CO2, CH4.
• cold, dusty, low on GHGs.
• warm, wet, more GHG.

Question 8

heinrich events

Answer 8

armadas of ice bergs in the north atlantic during the ice ages. find continental rock in mud.

Question 9

the ice ages lasted

Answer 9

2.7 million ybp to about 10,000 years ago. large ice sheets covered northwestern europe and norther north america.

Question 10

antarctic ice core record of past 800,000 years

Answer 10

• last glacial max: 20 kbp
• lack glacial min: 130 kbp
• CO2 and methane are low during ice ages
• ice ages are dusty

Question 11

the last glacial maxium (LGM) occured

Answer 11

around 20,000 years ago. sea level was lower by ~120 m at the time of the LGM because of the storage of water in the continental ice sheets.

Question 12

lake missoula

Answer 12

~18,000 ybp ice core at clark fork river.

Question 13

evidence of lake missoula flood

Answer 13

channeled scablands with lava plugs, potholes drilled by giant whirlpools, giant current ripples formed by deep, fast flowing water, and deep gorges with steep walls formed by flood: Multnomah Falls

Question 14

drumlin

Answer 14

an elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine. first recorded in 1833.

Question 15

glalcial erractic

Answer 15

piece of rock that differs from the size and type of rock native to the area in which it rests. carried by glacial ice, often over distances of hundreds of kilometers.

Question 16

ice core have been taken from

Answer 16

greenland and antarctica. up to 800,000 years old and up to 3,700 m deep.

Question 17

evaporation favors

Answer 17

light isotopes, rain favors heavy isotopes. cloud above ice is enriched in light isotopes.

Question 18

isotopes in ocean sediments record

Answer 18

glacial ice volume.

Question 19

isotopes in ice cores indicate

Answer 19

local temp.

Question 20

isotopic evidence: ice cores

Answer 20

• the water vapor in the atmosphere starts out with a certain fraction of heavy isotopes of O18 and Deuterium usually in the subtropics where its warm.
• as it moves along toward the ice sheet, it cools and the heavy isotopes condense, just like they are less likely to evaporate than heavier isotopes.
• the more it cools, the less heavy isotopes remain as the vapor condenses.
• so when it forms ice, the colder it has gotten, the less heavy isotopes.
• so more heavy isotope in ice means the air was warmer when the snow formed.

Question 21

huge temp. changes in ice ages:

Answer 21

up to 10 C in antarctica, 5 C globally.

Question 22

slow onset of

Answer 22

glacial periods and rapid decay. suggests that ice dynamics may play a role in the decay process (one reason we’re concerned about dynamic loss in greenland/ west antarctica).

Question 23

isotopic evidence: ocean sediments

Answer 23

• during an ice age water evaporates from the ocean and is deposited as ice on land. the lighter isotopes, O16 and H, evaporate first.
• the heavier isotopes get left behind, so ocean sediments get enriched in the heavy isotopes O18 and Deueterium (heavy hydrogen, has a neuron).
• so you can estimate the ice volume from the O18 ratio in ocean sediments. more O18 in ocean sediment, more land ice.

Question 24

can extend records back (to 3 million years) with

Answer 24

ocean sediment data.

Question 25

from oxygen isotopes in ocean sediments:

Answer 25

more frequent switching between glacial/interglacial before 600,000 years ago.

Question 26

carbon dioxide does not

Answer 26

drive ice ages, it is a feedback. CO2 changed due to temp. changes and amplified the changes (positive feedback).

Question 27

the driver of ice ages is

Answer 27

changes in solar radiation due to changes in earth’s orbit around the sun.

Question 28

solar radiation in the NH summer is key for

Answer 28

growth/melt of ice sheets.

• it’s always cold enough for snow in the winter at high latitudes, so winter temp. doesn’t matter.
• a colder summer means snow doesn’t melt and can accumulate.
• less sunlight in the summer means colder summers and expansion of high latitude ice sheets.
• and vice versa.

Question 29

theory of the ice ages:

Answer 29

orbital induced solar radiation changes and global ice volume.

• deglaciation events happen when there’s more summer sunlight.
• onset of ice ages occur when there’s less summer sun.

Question 30

tilt angle of earth is currently

Answer 30

23.44 degrees. tilt is the reason why we have seasons.

Question 31

tilt of axis of rotation varies from

Answer 31

22.5 to 24.5 degrees. dominant period of 41 kyr.

Question 32

higher tilt makes

Answer 32

summers hotter and winters colder, especially in high altitudes.

Question 33

currently at the middle of the road for tilt, but

Answer 33

tilt is decreasing and will reach its minimum in 8,000 years