Causes of ice age intensification across the Mid-Pleistocene Transition (original) (raw)
ADS
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- Hain, Mathis P. ;
- Foster, Gavin L. ;
- Rohling, Eelco J. ;
- Sexton, Philip F. ;
- Badger, Marcus P. S. ;
- Cherry, Soraya G. ;
- Hasenfratz, Adam P. ;
- Haug, Gerald H. ;
- Jaccard, Samuel L. ;
- Martínez-García, Alfredo ;
- Pälike, Heiko ;
- Pancost, Richard D. ;
- Wilson, Paul A.
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.
Publication:
Proceedings of the National Academy of Science
Pub Date:
December 2017
DOI:
Bibcode:
Keywords:
- boron isotopes;
- MPT;
- geochemistry;
- carbon dioxide;
- paleoclimate