Causes of ice age intensification across the Mid-Pleistocene Transition.

Tom B. Chalk, Mathis P. Hain, Gavin L. Foster, EJ Rohling, Philip F. Sexton, Marcus P.S. Badger, Soraya G. Cherry, Adam P. Hasenfratz, GH Haug, Samuel L. Jaccard, Alfredo Martínez-García, Heiko Pälike, Rich Pancost, Paul A. Wilson

Research output: Contribution to journalArticle (Academic Journal)peer-review

79 Citations (Scopus)
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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.
Original languageEnglish
Pages (from-to)13114-13119
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number50
Early online date27 Nov 2017
Publication statusPublished - 12 Dec 2017


  • paleoclimate
  • carbon dioxide
  • geochemistry
  • MPT
  • boron isotopes


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