Lect 4

Question 1

LGM

Answer 1

Last Glacial Maximum approx 21kyrs ago = max ice sheet extent

Likely causes:
Ice sheet presence (albedo feedback)
Lower atmospheric GHG’s (Co2)

Question 2

LGM Proxies

Answer 2

Loess
GHG’s
Veg
Sea surface temp
Monsoons

Question 3

Loess

Answer 3

Wind blown dust; covers 10% earth surface
Proxy for:
Dustiness, wildfires, wind characteristics, paleo ITCZ/Hadley Cell Location (formed at deserts)

Question 4

LGM Loess

Answer 4

Extensive sand dune deposition due to:

• dry climate and strong winds
• constricted Hadley Cells (and paleo-ITCZ) because

Question 5

Palynology

Answer 5

Study of pollen

Question 6

Pollen

Answer 6

Proxy for climates reconstruction:

• rain/temp control distribution of plants/pollen therefore can interpret based on species
• C14 date-able

Limitations:
Low resolution, affected by sediment

Question 7

Pollen-North US Lakes

Answer 7

Pollen curve shows:

• Lots of spruce (cold temp liking pollen) @ LGM, very little oak (warm temp plant)
• post LGM: lots of oak, little spruce

Question 8

Dryas Octopetla

Answer 8

Cold liking plant: Alpine/Tundra

[Jensen et al 1935]
Danish sed. Core shows:
Abundant Dryas pre-LGM, but none after; eliminated due to warming (Bolling Allerod) 
->reappears 12k BP and disappears again
——> = Younger Dryas Event

Question 9

Younger Dryas

Answer 9

Cooling followed by rapid warming approx 12k BP

Question 10

Younger Dryas Evidence

Answer 10

Dryas Octopetla (Pollen)
Mississippi delta 18O sed. core

Question 11

Younger Dryas Causes

3 Hypotheses

Answer 11

1) Thermohaline Circulation shutdown
2) YD Impact Hypothesis (YDIH)
3) Eruption

Question 12

Thermohaline Circ. shutdown

YD Cause 1

Answer 12

-meltwater entered N.Atlantic from pro-glacial lakes of N.Am
= lowered density and prevents sinking/NADW formation
Ultimately;
Less heat transferred to North

Question 13

YDIH

YD Cause 2

Answer 13

[Firestone et al 2017]
Bolide impact theory based on:
-carbon rich black soot layer
-microspherules

[Kennet et al 2008]
-nano diamonds in sediment

This evidence suggests and event like the Tunguska event (cometary airburst) or Chelyabinsk impact

Question 14

Eruption Hypothesis

YD Cause 3

Answer 14

[Baldini et al 2018]
Volcano in Germany (on edge of ice extent at YD) that is known to have erupted 12k years ago = Cause due to massive sulfur etc output

Advancing ice triggered cont.movement =eruption