1. Abrupt climate change

2. Abrupt climate change events during last glacial period (20-60kyr BP)
Dansgaard-Oeschger events (ice cores)
Heinrich events (ocean sediments)
Younger Dryas event

3. Ice cores: a record of past climate history
Snow turns into ice under pressure
Ice core drilling in EPICA, Antarctica: 800,000 yr of climate history

4. Dansgaard-Oeschger events

5. Global warming vs abrupt past climate change: D/O & Heinrich events
Amplitude
0.6C
10C
Duration of change
100 years
20 years

6. Heinrich events

7. Collecting the data: Deep sea cores CSS Hudson; gravity piston core

8. Cores stored in lab and retrieving a10m long gravity piston core

9. Deep Sea Drilling
Named for the Captain James Cook‘s HMS Resolution, 200 yrs ago. a derrick 61.5 m (202 ft) above water line; 143 m (469 ft) long; 21 m (68.9 ft) wide. Rig can suspend 9,150 m (30,020 ft) of drill pipe to ocean depth 8,235 m
Resolution Drill Ship, originally an oil exploration ship
operations days:
6,591
n. miles traveled
355,781
# of sites visited:
669
# of holes drilled:
1797
# recovered cores :
35,772

10. Micrograph of sand-size fraction in core HU87033-009.
Henrich’s 1988 cores from Dreizack seamounts: chain of extinct underwater volcanoes; 1000m above the sea floor; eastern North Atlantic, west of portugal
Micrograph of sand-size fraction in core HU
sand-size fraction from the same core at cm depth, within H-2.

11. Color and X-ray of lithic-rich sediments.
Heinrich (1988) discovered unexpectedly abrupt transitions between foraminifera & lithic sediments. Lithic sediments found at six depths. Changes are visible in color and X-rays: between dark-colored (foraminifera) & light-colored (lithic) segments.

12. Heinrich events (fraction of lithic material as function of time)
How did these continental sand/ rocks get to the middle of the ocean??

13. Spatial extent of Heinrich layers

14. Source of lithic sediments: icebergs released from land ice

16. Source of ice rafted debri: “Dirty ice”
East Greenland: We seldom think of icebergs as dirty, and with good reason: only some icebergs contain debris, and even then, only in a 1-2m layer like that which is plainly visible in this iceberg.

17. Heinrich “teleconnections”

18. Mechanism of Heinrich events: The Binge/ Purge Oscillator:
The mechanism of periodic ice discharges from Laurentide ice sheet (Doug MacAyeal 1993):

19. Which is what?
Dansgaard/ Oeschger (DO) events: abrupt warming events seen in Greenland ice cores every ~1,500 years. Warming occurs within 20 years, and lasts years.
Heinrich events are massive releases of icebergs into North Atlantic ocean from Laurentide ice sheet and possibly others. Occurs every ~7,000-10,000 years
Are they linked?

20. Climate effects of Heinrich events; Possible link between Heinrich and D/O events:
 Some of the larger D/O warming events seem to follow and perhaps result from Heinrich events:

21. Connection between D/O and Heinrich events: the “bond cycle”
No satisfactory explanation currently exists for this cycle…

22. Mechanism of D/O warming events in Greenland ice cores

23. Two alternative explanations to observed abrupt warmings: 1: Thermohaline circulation
Density=-Temperature+Salinity;
THC: driven by temperature gradients due to atmc heating & cooling. braked by salinity gradients due to evaporation & precipitation.
Transport = 20Sv (world rivers combined = 1Sv =10^6m^3/sec)
Large heat transport from equator to poles.

24. Two alternative explanations to observed abrupt warmings: 2: sea ice
Sea ice albedo:
Sea LGM:
Sea ice pancakes:

26. Younger Dryas
Abrupt return to glacial conditions in the northern north Atlantic at around 12,900 – 11,500 yr BP; some related climate signals in many areas around globe
Due to weakening of thermohaline circulation and expansion of sea ice?

27. Finally, the good(?) news about D/O events
Some scientists suggested that global warming may result in an unstable climate, as during the last glacial maximum:
However, this is not likely if D/O events were caused by sea ice changes around Greenland. Sea ice is expected to melt even in the arctic within years
Is this good news…?

28. Sea ice and global warming
Arctic sea ice animation from satellite data:
winter: smallest sea ice recovery on record
Arctic sea ice area shrinking by some 25% from 1979 to 2005