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

The last 7 glacial cycles from foram  18 O Lisiecki & Raymo,

THE DISCOVERY OF HEINRICH EVENTS….

…. IN MARINE SEDIMENT ARCHIVES

Transport of ice-rafted debris (IRD)

“IRD Belt” - based on network of N. Atlantic marine sediment records Site with ice-rafted debris Site without ice-rafted debris

HEINRICH EVENT CHRONOLOGY IRD peaks Bond et al. (1992)

Dansgaard-Oeschger Cycles discovered in Greenland ice  18 O ice warmcold

Bond and Lotti (1995) COLDER BOND 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 Temperatures H-events occurred during extreme cold phases of D-O cycles in Greenland ice cooler warmer

HEINRICH 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 BASIN Increased bioturbation suggesting higher O 2 levels (D-O interstadials show the opposite with reduced bioturbation) Increased  18 O benthic Increased Pacific ventilation?

GLOBAL SIGNATURE OF D/O EVENTS: CARIACO BASIN

GLOBAL SIGNATURE OF D/O EVENTS: ARABIAN SEA Total organic carbon (TOC) records from two marine sediment cores off Pakistan showing millennial- scale variability of monsoonal surface water productivity and bottom-water oxygen laminated bioturbated Increased prod., lower O 2 Greenland  18 O ice

Wang et al, 2001 Chinese monsoon and the shifting of the ITCZ

ICE SHEET STABILITY: THE BINGE-PURGE THEORY MacAyeal’s explanation for Heinrich Events ~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 PURGE BINGE

THERMOHALINE 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 Circulation Oc/Atm Atm

SOLAR VARIABILITY: IRD and Cosmogenic Nuclides in the Holocene 10 Be 14 C Bond et al. (2001) Similar pacing of ice rafting events during last interglacial (MIS-5)

TROPICAL DYNAMICS: EASTERN TROPICAL PACIFIC The Idea: El Ni ñ o/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)