Abrupt Climate Change Evidence of climate changes that are too abrupt to be explained orbitally.

Abrupt Climate ChangeEvidence of climate changes that are too abrupt to be explained orbitally.

The last 7 glacial cycles from foram 18O

Lisiecki & Raymo, 2005

3.25

5.25

4.25

THE DISCOVERY OF HEINRICH EVENTS….THE DISCOVERY OF HEINRICH EVENTS….

……. IN MARINE SEDIMENT ARCHIVES. IN MARINE SEDIMENT ARCHIVES

Transport of ice-rafted debris (IRD)Transport of ice-rafted debris (IRD)

““IRD Belt” - based on IRD Belt” - based on network of N. Atlantic network of N. Atlantic marine sediment recordsmarine sediment records

Site withice-rafteddebris

Site withoutice-rafteddebris

HEINRICH EVENT CHRONOLOGYHEINRICH EVENT CHRONOLOGY

IRD peaks

Bond et al. (1992)

Dansgaard-OeschgerDansgaard-Oeschger CyclesCycles discovered in Greenland ice discovered in Greenland ice

18Oicewarmcold

Bond and Lotti (1995)

COLDER COLDER

BOND IDENTIFIES MORE IRD PEAKS IN N. ATLANTIC SEDIMENTSBOND IDENTIFIES MORE IRD PEAKS IN N. ATLANTIC SEDIMENTS

In addition to Heinrich events (Huge IRD peaks, cold Greenland air temp. and cold N. Atl. SST)…

Cold phases of D-O cycles - smaller amplitude IRD peaks; smaller SST signal

N. Atlantic SSTs track Greenland Air TemperaturesH-events occurred during extreme cold phases of D-O cycles in Greenland ice

cool

erw

arm

er

HEINRICH EVENTSHEINRICH EVENTS• Hartmut Heinrich discovered a cyclic pattern of ice-rafted debris over the last 130 ky in a series of sediment records from the North Atlantic

• Broecker and Bond later identified six of these events between 70 and 14 ky B.P., and named them Heinrich events (H1-H6)

• Heinrich events occur every ~7-10 ky, and are associated with pronounced cooling in the Greenland ice core records and North Atlantic region

• Bond et al. (1993) noted that Heinrich events appear to occur towards the end of increasingly colder D-O cycles

Blunier and Brook, 2001

Greenland and Antarctic‘antiphased’

THE YOUNGER DRYAS IN THE SANTA BARBARA BASINTHE YOUNGER DRYAS IN THE SANTA BARBARA BASIN

• Increased bioturbation suggesting higher O2

levels (D-O interstadials show the opposite with reduced bioturbation)

• Increased 18Obenthic

• Increased Pacific ventilation?

GLOBAL SIGNATURE OF D/O EVENTS: CARIACO BASINGLOBAL SIGNATURE OF D/O EVENTS: CARIACO BASIN

GLOBAL SIGNATURE OF D/O EVENTS: ARABIAN SEAGLOBAL SIGNATURE OF D/O EVENTS: ARABIAN SEA

Total organic carbon Total organic carbon (TOC) records from (TOC) records from two marine sediment two marine sediment cores off Pakistan cores off Pakistan showing millennial-showing millennial-scale variability of scale variability of monsoonal surface monsoonal surface water productivity water productivity and bottom-water and bottom-water oxygenoxygenlaminatedbioturbated

Increased prod., lower O2

Greenland Greenland 1818OOiceice

Wang et al, 2001

Chinese monsoon andthe shifting of the ITCZ

ICE SHEET STABILITY: THE BINGE-PURGE THEORYICE SHEET STABILITY: THE BINGE-PURGE THEORYMacAyeal’s explanation for Heinrich Events

~7 ky pacing

~7 ky pacing

Laurentide Ice Sheet (LIS) Model:

Binge (Growth) phase - basal sediment frozen, ice sheet immobile; slow growth of LIS

Purge phase - geothermal flux gradually increases basal temperature, thawing basal sediments; rapid discharge of icebergs; (meltwater input reduces THC, cool North Atlantic, allowing ice growth again)

BINGE

PU

RG

EP

UR

GEBIN

GE

THERMOHALINE CIRCULATION: THE SALT OSCILLATORTHERMOHALINE CIRCULATION: THE SALT OSCILLATOR

Conveyor On: Northward heat transport initiates ice melting, which reduces density of upper ocean, reducing deep water formation

Conveyor Off: Cooling of North Atlantic (less melt water input) and reduced salt export gradually increase density (and thus deep water formation); return to Conveyor On mode

Three Modes of North Atlantic Deep Ocean CirculationThree Modes of North Atlantic Deep Ocean Circulation

Oc/AtmAtm

SOLAR VARIABILITY: IRD and Cosmogenic Nuclides in the Holocene SOLAR VARIABILITY: IRD and Cosmogenic Nuclides in the Holocene

10Be

14C

Bond et al. (2001)Similar pacing of ice rafting events during last interglacial (MIS-5)

TROPICAL DYNAMICS: EASTERN TROPICAL PACIFICTROPICAL DYNAMICS: EASTERN TROPICAL PACIFIC

The Idea: El Niño/Southern Oscillation (ENSO) system in the eastern tropical Pacific affects tropical SST distribution, which controls convection/atmospheric circulation patterns - very strong teleconnections, which could explain near-global synchroneity of millennial events

Experiment: Coupled ocean-atmosphere model of the tropical Pacific is run for 150,000 years, both with and without orbital (precession) forcing

Result: Millennial increases or decreases in the frequency of ENSO warm or cold events and changes in their amplitudes

EVENT AMPLITUDE

EVENT FREQUENCY

Clement et al. (1999)