Talk by Dr. Tommaso Alberti

(INAF-Istituto di Astrofisica e Planetologia Spaziali Area di Ricerca Roma Tor Vergata)

Title: "Exploring the middle Pleistocene transition"

The Earth's climate is an extremely unstable complex system consisting of nonlinear and still rather unknown interactions among atmosphere, land surface, ice and oceans. Several external and internal components lead variations in temperature from decadal to multi-millennial timescales with differences between glacial and interglacial climates [Shao and Ditlevsen, 2016]. On multi-millennial timescales, glacial cycles are related to periodic and quasi-periodic changes in the insolation due to variations in Earth's orbit around the Sun. Particularly, the climate response is ∼100 kyr glacial cycles since the middle Pleistocene transition (MPT) around 1 Myr ago, where the climate has shifted regularly between the glacial and interglacial climate states, while prior to 1 Myr BP a "41-kyr world" was observed.

This observed behavior does not indicate any noticeable difference in the orbital forcing, with the climate response appearing far from to be structurally different before and after the MPT.

Here, we applied the Empirical Mode Decomposition (EMD) to the global ocean benthic foraminifera δ 18 O stack record [Lisiecki and Raymo, 2005], which is a proxy for the global ice volume. We analyse the time series during the last 2 Ma to investigate amplitude-frequency changes between glacial and interglacial climate states. We found that both 41-kyr and 100-kyr periodicities are present during the last 2 Ma although amplitudes changes in time producing the well-known separation between "100-kyr world" and "41-kyr world", while no changes in frequency are observed.

 From a dynamical system point of view we found that both 41-kyr and 100-kyr components can be seen as a single-state forcing. Interestingly, we also found a larger timescales component which is characterized by smooth transitions between three different climate states, in agreement with previous works [Paillard, 1998; Ashwin and Ditlevsen, 2015].  

References

  • Shao, Z.G. and Ditlevsen, P.D., Nature Commun., 7, 10951 (2016).
  • Lisiecki, L. E. and Raymo, M. E., Paleoceanography, 20, PA1003 (2005).
  • Paillard, D., Nature, 391, 378-381 (1998).
  • Ashwin, P. and Ditlevsen, P.D., Climate Dynamics, 45, 2683-2695 (2015).