Stratigraphy of climate change
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Stratigraphy of climate change. Lecture 19. The predominant power in this spectrum is at about 100,000, 41,000 and 19-23,000 years. from Alley, 2000. The Milankovitch hypothesis: climate change results from changes in Earth’s orbital parameters. Barbados.

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from Alley, 2000 41,000 and 19-23,000 years

The Milankovitch hypothesis: climate change results from changes in Earth’s orbital parameters

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Barbados 41,000 and 19-23,000 years

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Today we’ll look at examples of climate changes seen in the stratigraphic record that are NOT controlled by orbital parameters

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Orbital Forcing – Ice Cores the stratigraphic record that are NOT controlled by orbital parameters

  • Ice core 18O records temperature

  • Orbital frequencies are clearly dominant, but higher frequencies are present

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Heinrich Events the stratigraphic record that are NOT controlled by orbital parameters

  • Discovered in 1988 in marine sediment cores

  • Recognized as distinct layers with significant increase in lithic fragments, and large clasts in some areas

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Heinrich Layer Isopachs the stratigraphic record that are NOT controlled by orbital parameters

  • Double maxima in isopachs

  • Layers thicken to NW into Labrador Sea

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Source of Heinrich events the stratigraphic record that are NOT controlled by orbital parameters

  • Black areas are regions with large carbonate deposits

  • Sediment must have been ice-rafted

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Heinrich Layer 4 (~40,000 years BP) the stratigraphic record that are NOT controlled by orbital parameters

18O in polar planktonic foraminifera

Modeling shows about 250-year duration and 2-m rise in sea level

Nature, Roche et al., 2004

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Heinrich Events in context level

  • Occur at times of coldest weather in N. Atlantic

  • Followed by a sharp warming

  • No clear periodicity

Bond 1993 figure

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Summary of Heinrich events level

  • Effects are global – signature of Heinrich events has been found around the world

  • Massive discharge of ice into N. Atlantic from the Laurentide ice sheet is well established

  • No clear explanation for such dynamics in the ice sheet

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Dansgaard-Oeschger Events level

  • Characterized by rapid warming in the N. Atlantic, followed by slower cooling

  • Quasi-Periodic, with a timescale of ~1400 years

  • Recorded by diverse climate proxies

  • Evidence for global climatic effects

(Data From

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Greenland and D-O events level

  • Within the Greenland ice cores, several independent variables all show D-O events prominently

    • 18O – Temperature

    • Ca/Dust concentrations – varying weather in Asia?

    • Na/Cl concentrations – increased storminess in N. Atlantic

    • Etc…

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Other Evidence of D-O events level

  • Sediment cores from the Santa Barbara Basin (Hendy and Kennet, 1999)

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Other Evidence of D-O events level

  • Stalagmites from Eastern China (Wang et al., 2001)

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Global Map of D-O records level

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Theories for rapid climate change level

  • Heinrich, D-O periods are too rapid for orbital frequencies

  • Some combination of the ocean/atmosphere/cryosphere must be responsible

  • Need a source with enough power to affect global climate

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Deep water formation level

Atlantic Circulation

  • Deep Water is formed at the Northern and Southern extents of the Atlantic Ocean

  • This deep circulation has an overturning timescale of ~103 years

  • Surface currents strongly influence climate in many areas, as in the N. Atlantic

Deep water formation

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Stratigraphic Evidence level

  • Recent work (April 2004) has investigated a proxy for Atlantic circulation using a marine sediment core from the Bermuda Rise

  • Th settles out of water faster than Pa, so the ratio between the two can provide information about the strength of flow away from source

  • Result – Atlantic circulation essentially shut down during Heinrich events

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Summary level

  • There is still no clear trigger for Heinrich or Dansgaard-Oeschger events, nor an explanation for their periods

  • However, changes in Atlantic circulation seem to account for many of the side effects of both processes

  • More stratigraphic records = more clues

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End of Agriculture??? level

Why it all matters

Beginning of Agriculture

  • Late Pleistocene was not simply cold – it was totally chaotic

  • Even modern agricultural processes probably couldn’t overcome such variability

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A few references… level

  • Bradley, Raymond S. Paleoclimatology. Harcourt Press, 1999.

  • Siedov et al., Ed. The Oceans and rapid climate change. AGU, 2001.

  • Hesse, R. and Khodabakhsh, S. Depositional Facies of Late Pleistocene Heinrich Events I nthe Labrador Sea. Geology 26:2 103-106, 1998.

  • Dansgaard, W et al. Evidence for general instability of past climate from a 250kyr ice-core record. Nature 364, 15 July 1993.

  • Bond, G. et al. Evidence for massive discharges of icebergs into the North Atlantic Ocean during the last glacial period. Nature 360, 19 Nov. 1992.

  • Sarnthein, M. et al. Exploring Late Pleistocene Climate Variations. Eos. 81:51 2000.

  • Bond, G. et al. Correlations between climate records from North Atlantic sediments and Greenland ice. Nature 365, 9 Sept. 1993.

  • Bard, E. Climate Shock: Abrupt changes over Millennial time scales. Physics Today Dec. 2002.

  • Hendy and Kennett. Dansgaard-Oeschger cycles and the California Current System: Planktonic foraminiferal response to rapid climate change in Santa Barbara Basin, Ocean Drilling Program hole 893A. Paleoceanography, 15:1, 2000.

  • Phillips, FM. Climatic and hydrologic oscillations in the Owens Lake basin and adjacent Sierra Nevada, California. Science 274:5288, 1996.

  • Wang, YJ. A High-Resolution Absolute-Dated Late Pleistocene Monsoon Record from Hulu Cave, China. 294:5550, 2001.