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High Latitude Insolation and Climate Response

High Latitude Insolation and Climate Response. 23 April 2009 /// EAS 4803 Sean Miller. Introduction. Milankovitch: high latitude NH summer insolation drives glacial-interglacial cycles Changes in precession (19-23 kyr cycle), obliquity (41 kyrs), eccentricity (100 kyrs) are important

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High Latitude Insolation and Climate Response

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  1. High Latitude Insolation and Climate Response 23 April 2009 /// EAS 4803 Sean Miller

  2. Introduction • Milankovitch: high latitude NH summer insolation drives glacial-interglacial cycles • Changes in precession (19-23 kyr cycle), obliquity (41 kyrs), eccentricity (100 kyrs) are important • Marine benthic foraminifera δ18O used to track global ice volume changes

  3. Introduction • Eccentricity: Orbit Shape • Obliquity: Axial Tilt • Precession: Direction of Axis • All change slowly over time http://www.sciencecourseware.org/eec/GlobalWarming/Tutorials/Milankovitch

  4. Data • δ18O from Benthic Foraminifera • δ18O : Oxygen Isotope Ratio • Tracks global ice volume variability • Lighter δ18O values suggest more precipitation over ice sheet • Recorded every 1 kyr • 780 ky of data • 60ºN June Insolation • Insolation received during NH high latitude summer • Recorded every 1 kyr • 1000 kyr of data http://en.wikipedia.org/wiki/File:Benthic_foraminifera.jpg

  5. Methods • Create matrix of data • Detrend data • Fourier Power Spectrum • plot periodograms • Cross-Spectral Analysis • cpsd • Coherence • mscohere

  6. Time Series

  7. Spectral Analysis Functions used: interp1, detrend, periodogram, xcov 1 2 3 2 1 3 4 • δ18O Signal of NH Ice Volume • 1 – 87.0 kyr (Strongest) • 2 – 39.1 kyr • 3 – 23.0 kyr • 4 – 18.6 kyr • 60ºN June Insolation Changes • 1 – 40.0 kyr • 2 – 23.3 kyr (Strongest) • 3 – 18.9 kyr

  8. Cross-Spectral Analysis Functions used: detrend, cpsd, mscohere • 1 – 97.7 kyr  eccentricity? • 2 – 41.1 kyr  obliquity • 3 – 23.0 kyr  precession • The 23 year cycle has frequencies that show greatest variability among the two datasets. • Variability is also noted at 41.1 and 97.7 kyr. • All three peaks are coherent. 3 2 1

  9. Results • Proxy data have cycles with 87, 39, 21, and 19 kyr periodicities • Insolation data have cycles with 40, 23, and 19 kyr periodicities • Cross-Spectral Analysis shows 98, 41, and 23 kyr periodicities

  10. Discussion • Strongest signal varied mainly at 23 kyrs • Suggests ice volume response to precession • 41 kyr signal • Suggests ice volume response to obliquity • 90-100 kyr signal • More complicated • No peak in 60ºN insolation data • Pronounced peak in paleoproxy record • Possibly from internal feedbacks within the ice sheets themselves • Ice sheets are non-linear systems

  11. References • Berger A. and Loutre M.F., “Insolation values for the climate of the last 10 million years.” Quaternary Sciences Review, Vol. 10 No. 4 pp. 297-317, 1991 • Imbrie, J. Hays, J.D. Martinson, D.G., McIntyre, A., Mix, A. C, Morely, J.J, Pisias, N.G., Prell, W. L., and Shackleton, N. J., “The Orbital theory of Pleistocene climate: support from a revised chronology of the marine δ18O record. In Berger, A., Imbrie, J., Hays, J., Kulka, G., and Saltzman, B., (Eds.), Milonkovitch and Climate (Part 1)”. NATO ASI Ser. C, Math Phys. Sci., 126:269-305, 1984 • Ruddiman, William F., Earth’s Climate Past and Future, New York: W.H. Freeman and Company, 2008 • Ruddiman, W.F. Orbital insolation, ice volume, and greenhouse gases. Quaternary Science Reviews, 22(15), pp 1597-1629.

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