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Abrupt Climate Change

Abrupt Climate Change. Evidence of climate changes that are too abrupt to be explained orbitally. 3.25. 4.25. 5.25. Lisiecki & Raymo, 2005. The last 7 glacial cycles from foram  18 O. THE DISCOVERY OF HEINRICH EVENTS…. …. IN MARINE SEDIMENT ARCHIVES. Transport of ice-rafted debris (IRD).

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Abrupt Climate Change

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

  2. 3.25 4.25 5.25 Lisiecki & Raymo, 2005 The last 7 glacial cycles from foram 18O

  3. THE DISCOVERY OF HEINRICH EVENTS….

  4. …. IN MARINE SEDIMENT ARCHIVES

  5. Transport of ice-rafted debris (IRD)

  6. “IRD Belt” - based on network of N. Atlantic marine sediment records Site withoutice-rafteddebris Site withice-rafteddebris

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

  8. Dansgaard-OeschgerCycles discovered in Greenland ice cold warm d18Oice

  9. 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 COLDER COLDER Bond and Lotti (1995)

  10. H-events occurred during extreme cold phases of D-O cycles in Greenland ice N. Atlantic SSTs track Greenland Air Temperatures warmer cooler

  11. 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 HEINRICH EVENTS

  12. Greenland and Antarctic ‘antiphased’ Blunier and Brook, 2001

  13. THE 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?

  14. GLOBAL SIGNATURE OF D/O EVENTS: CARIACO BASIN

  15. Increased prod., lower O2 laminated bioturbated GLOBAL SIGNATURE OF D/O EVENTS: ARABIAN SEA Greenland d18Oice 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

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

  17. ~7 ky pacing ~7 ky pacing ICE SHEET STABILITY: THE BINGE-PURGE THEORY MacAyeal’s explanation for Heinrich Events BINGE PURGE 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

  18. 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

  19. Three Modes of North Atlantic Deep Ocean Circulation Oc/Atm Atm

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

  21. TROPICAL 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 FREQUENCY EVENT AMPLITUDE Clement et al. (1999)

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