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)