The Quaternary Ice Age

Question 1

Last GM and Interglacial dates?

Answer 1

LGM: 18,000 years BP

Last interglacial 125,000 years BP

Question 2

When and what was the Younger Dryas?

Answer 2

15,000 Years BP and an exceptionally cold period

Question 3

Placing it together: The last interglacial

Answer 3

• Many attempts to correlate marine timescales to terrestrial records
• Terrestrial interglacial extended into MIS 5d
• Evidence provided a broad range of times for Last Interglacial duration (11kyr – 23kyr)
• Poor chronologies were the main problem

The accurate U-Th chronology possible with stalagmites has helped to constrain low-latitude terrestrial climate change

Question 4

EPICA what is it and what are the results?

Answer 4

o Actual past atmosphere concentrations taken from bubbles
o Modern CO2 concentrations 30% higher than at any point in last 650,000 years
 CO2 never drops below 180 or above 300 (now at 400)
• = Anthropogenic
o CO2 and temperature strongly coupled
 Again, means anthropogenic

Question 5

Co2 results from ice cores?

Answer 5

• Carbon dioxide very well correlated with temperature over last 450 ka. (Vostok)
• Carbon dioxide very well correlated with temperature over last 15,000 years (Taylor Dome)
• Carbon dioxide very well correlated with temperature over last 40 years (instrumental)
• So is carbon dioxide the principal driver of Quaternary Climate Change

Question 6

Problems with ice cores

Answer 6

• Provides both T and CO2 information but:
o Ice must reach a closure depth before it is sealed from the atmosphere
o Until this depth is reached the CO2 will continue to mix with the atmosphere
• Delta 18O represents T at time but CO2 represents atmosphere a couple of decades after
• Can be corrected however
• This was done and it was found that CO2 and temp change before ice

Question 7

Current paradigm on Co2 temperature relationship

Answer 7

• Temperature begins to change around 800 years before CO2
• CO2 first responds to T, or deglaciation
• But…does CO2 then drive the positive feedback?
• CO2 probably drives most of g-ig climate change – but does not initiate it

Question 8

Glacial worlds and the carbon problem

Answer 8

• Glacial world a very low biomass system
• The d13C of deep sea sediment cores indicates an influx of ‘light’ carbon at glacial terminations
• Where did this carbon come from?
• Interglacial CO2 increased by 80 ppmv, or 170 gigatonnes C (GtC)
• The total amount of carbon emitted to the atmosphere by fossil fuel burning between 1860-1997 is 290 GtC, so interglacial increase is ca 60% of this.

Question 9

Some proposed explanations for CO2 increase in glacial worlds

Answer 9

• Exclusively from degassing of CO2 from oceans
• ‘Clathrate Gun’ Hypothesis
• Iron Fertilization Hypothesis
• Terrestrial Biomass Hypothesis
Some of these are climate engineering ideas

Question 10

Degassing of CO2 from oceans (CO2 increase technique)

Answer 10

• CO2 is more soluble in cold water = cold ocean = more co2 in = cools oceans = feedback
• Also works with warming
• Insolation T increase of 1ºC will produce between 10 and 20 ppm carbon dioxide, far short of the observed g-ig increase of 80 ppm
• So although oceanic degassing undoubtedly does add CO2 to the atmosphere, it is not the primary source.

Question 11

Iron Fertilization Hypothesis

Answer 11

• Parts of the Southern Ocean are designated as “High Nutrient, Low Chlorophyll” (HNLC) – iron tends to be the limiting agent on bioproductivity
• ‘Iron Fertilization’ Hypothesis states that increased dust influx during glacial periods alleviates the iron limitation in HNLC areas
• Increased uptake of atmospheric CO2 during glacial periods and export production (carbon exported to seafloor) decreases atmospheric CO2

Question 12

Pros and Cons of iron fertilisation hypothesis?

Answer 12

PROS
• Modern experimental evidence demonstrates that iron fertilization does result in phytoplankton blooms and CO2 sequestration
• Explains observed increase in foraminiferal d13C during glacial periods (more light biogenic C being absorbed by plankton)

CONS
• Periods of increased dust flux do not seem to coincide with periods of decreased carbon dioxide
• Various models (Kohfeld et al., 2005) suggest that any kind of increased export production model only explains about 50% of observed CO2 decrease during glacials
• Increased dust input must arise from already changed biomes. Hypothesis does not account for this initial change

Question 13

Terrestrial Biomass Hypothesis

Answer 13

• During glaciations fewer carbon sinks exist due reduced terrestrial biomass: any CO2 produced would linger longer in atmosphere
• Earth warms, deglaciates and more terrestrial biomes form
• CO2 once again stored in biosphere reserves (peat, boreal forest).
• Temperature slowly begins decreasing

Question 14

Ocean circulation changes (CO2 sink)

Answer 14

• Carbon cycle basics understood but scales and new sources constantly being redefined and discovered
• Reduced ocean circulation during glacial periods
• Gradually increasing oxygen circulation could release substantial deep ocean CO2 to atmosphere

Question 15

Other ‘biological pump’ hypotheses

Answer 15

• Whole-Ocean Nutrient Increase Theory
• Nutrient Utilization
• CaCO3 / Corg Rain Ratio
• Silica Leakage Hypothesis
• But all account for less than 50% of observed CO2 g-ig variability

Question 16

DO events?

Answer 16

• Dansgaard Oeschger Events (DO events)
o ‘Sawtooth’ shaped
o Rapid warming
o Gradual cooling
o Millennial Scale
o 23 identified between 110 and 23 ka BP
• DO events initiate by Ice Rafting events?
o Ice rafted IRD sediment deposition in Atlantic
• IRD events coincide with warming
• Implication: ice sheets play role in millennial climate fluctuations

Question 17

Heinrich Events

Answer 17

o Six Events (H1 to H6)
o All defined by ratio of grains in N. Atlantic sediment
o Massive iceberg events
o All seem to initiate warming

Question 18

Channeled Scablands features

Answer 18

Enigmatic geomorphological features

o Heavily eroded region
o Lakes and scours – not glaciation
o Waterfalls – ‘dryfalls’
o Giant ripple marks

Question 19

J Harlen Bretz - his story

Answer 19

o Interpreted evidence as catastrophic flooding in the 1920s
o Canyons = huge river channels
o Hundreds of extinct waterfalls
o Removal of loess hundreds of feet deep
o Anastomosis due to huge volume of water
o Presented evidence at GSA in 1927. The response was overwhelmingly negative – no source
o For 13 years no one believed a flood of this magnitude could occur
o Joe Pardee mapped area to the east of Channeled Scablands as a huge glacial lake – provided source for water

Question 20

Glacial Lake Missoula Floods

Answer 20

o Glacial Lake Missoula forms behind a southern extension of Cordilleran Ice Sheet – the Purcell Lobe
o When water gets deep enough the ice dam floated upwards
o Water escaped from underneath
o Lake drains
o Flood produces ten times combined flow of all the rivers in the world
o Lake refilled as ice readvanced
o Lake filled and emptied 55 times in 2,000 years (from 15 ka BP)

Streamlined Scabland Hills seen on Mars = Mars had water

Question 21

Deglacial Meltwater Releases

Answer 21

Meltwater pulse 1a
o Sea level rose 25m in 500 yrs
o ~14 ka BP
o Maybe from Greenland?
o Probably from Antarctica
Younger Dryas
o Freshwater discharge from Proglacial Lakes Agassiz and Ojibway
8.2 ka event – larges climate excursion of holocene
o 100x as great as Lake Missoula flood
o Freshwater discharge from Lakes Agassiz and Ojibway

Question 22

8.2Ka Event

Answer 22

o The event is believed to have been caused by the catastrophic drainage of large proglacial lakes in Canada.
o Around 8,400 years before present, the remnants of the Laurentide Ice Sheets formed a large ice dome over the modern day location of Hudson Bay.
o On the southern fringes of the ice sheet were located several large proglacial lakes, the largest of which were lakes agassiz and ojibway.
o Together they contained 5x as much freshwater as the modern day great lakes.
o Around 8,200 years BP the ice dome collapsed, catastrophically releasing 4.67 x 10^14 cubic metres of water through the Hudson Strait into the North Atlantic. According to some estimates global sea level rose by almost ½ of a metre within two days of the event. However, what caused the climate to change dramatically was the location the freshwater entered the North Atlantic
o The injection of low-density fresh water at a high latitude prevents the sinking and formation of the NADW, weakening or shutting down the North Atlantics conveyor belt. Warm water no longer flows into the higher latitudes, resulting in a colder, drier climate
o Temperature models show 8-degree maximum cooling associated with the 8,200 year event, as well as a 5 degree N Hemispheric cooling.
o Proxy data suggests drier conditions throughout the N atlantic.

Question 23

Thermohaline conveyor belt:

Answer 23

o Warm water flow northward as part of the gulf stream, eventually separating into the North Atlantic drift. The warm water continues northward, becomes colder and denser, eventually sinking to form the NADW, which then flows back to the low latitudes.
o It’s this conveyor of warm water to the north and cold water to the south that provides Ireland with its genial albeit wet climate.
o If you shut off the belt, then warm water will stop travelling to the North = easy cooling

Question 24

G-IG Asymmetry

Answer 24

o Most glaciations end quickly
o Interglacials end very slowly
o Whatever the mechanism, G-IG variability involves the carbon cycle