Causes of ice age intensification across the Mid-Pleistocene Transition

Thomas B Chalk; Mathis P Hain; Gavin L Foster; Eelco J Rohling; Philip F Sexton; Marcus P S Badger; Soraya G Cherry; Adam P Hasenfratz; Gerald H Haug; Samuel L Jaccard; Alfredo Martínez-García; Heiko Pälike; Richard D Pancost; Paul A Wilson

doi:10.1073/pnas.1702143114

Causes of ice age intensification across the Mid-Pleistocene Transition

Proc Natl Acad Sci U S A. 2017 Dec 12;114(50):13114-13119. doi: 10.1073/pnas.1702143114. Epub 2017 Nov 27.

Authors

Thomas B Chalk^{1

2}, Mathis P Hain¹, Gavin L Foster³, Eelco J Rohling^{3

4}, Philip F Sexton⁵, Marcus P S Badger^{5

6}, Soraya G Cherry³, Adam P Hasenfratz⁷, Gerald H Haug⁸, Samuel L Jaccard^{9

10}, Alfredo Martínez-García⁸, Heiko Pälike^{3

11}, Richard D Pancost⁶, Paul A Wilson³

Affiliations

¹ Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom; T.chalk@noc.soton.ac.uk M.P.Hain@soton.ac.uk.
² Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.
³ Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom.
⁴ Research School of Earth Sciences, The Australian National University, Canberra 2601, Australia.
⁵ School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom.
⁶ Organic Geochemistry Unit, School of Chemistry, The Cabot Institute, University of Bristol, Bristol BS8 1TS, United Kingdom.
⁷ Geologisches Institut, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland.
⁸ Max Planck Institut für Chemie, 55128 Mainz, Germany.
⁹ Institute of Geological Sciences, University of Bern, 3012 Bern, Switzerland.
¹⁰ Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland.
¹¹ Center for Marine Environmental Sciences (MARUM), University of Bremen, 28359 Bremen, Germany.

Abstract

During the Mid-Pleistocene Transition (MPT; 1,200-800 kya), Earth's orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO₂ levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO₂ data to show that the glacial to interglacial CO₂ difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO₂ levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO₂-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO₂ change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.

Keywords: MPT; boron isotopes; carbon dioxide; geochemistry; paleoclimate.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.
Research Support, Non-U.S. Gov't