Abrupt climate change http://www.ngdc.noaa.gov/paleo/slides/slideset/index19.htm

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

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

Dansgaard-Oeschger events

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

Heinrich events

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

Cores stored in lab and retrieving a10m long gravity piston core

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

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 HU87033-009. sand-size fraction from the same core at 670-672 cm depth, within H-2.

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.

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

Spatial extent of Heinrich layers

Source of lithic sediments: icebergs released from land ice

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.

Heinrich “teleconnections”

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

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 500-1000 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?

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:

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

Mechanism of D/O warming events in Greenland ice cores

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.

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

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?

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 50-100 years Is this good news…?

Sea ice and global warming Arctic sea ice animation from satellite data: 2004-2005 winter: smallest sea ice recovery on record Arctic sea ice area shrinking by some 25% from 1979 to 2005