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

Autor:	Chalk TB; 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.; Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543., Hain MP; 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., Foster GL; Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom., Rohling EJ; Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom.; Research School of Earth Sciences, The Australian National University, Canberra 2601, Australia., Sexton PF; School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom., Badger MPS; School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom.; Organic Geochemistry Unit, School of Chemistry, The Cabot Institute, University of Bristol, Bristol BS8 1TS, United Kingdom., Cherry SG; Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom., Hasenfratz AP; Geologisches Institut, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland., Haug GH; Max Planck Institut für Chemie, 55128 Mainz, Germany., Jaccard SL; Institute of Geological Sciences, University of Bern, 3012 Bern, Switzerland.; Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland., Martínez-García A; Max Planck Institut für Chemie, 55128 Mainz, Germany., Pälike H; Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom.; Center for Marine Environmental Sciences (MARUM), University of Bremen, 28359 Bremen, Germany., Pancost RD; Organic Geochemistry Unit, School of Chemistry, The Cabot Institute, University of Bristol, Bristol BS8 1TS, United Kingdom., Wilson PA; Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom.
Jazyk:	angličtina
Zdroj:	Proceedings of the National Academy of Sciences of the United States of America [Proc Natl Acad Sci U S A] 2017 Dec 12; Vol. 114 (50), pp. 13114-13119. Date of Electronic Publication: 2017 Nov 27.
DOI:	10.1073/pnas.1702143114
Abstrakt:	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 CO 2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO 2 data to show that the glacial to interglacial CO 2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO 2 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 CO 2 -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 CO 2 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. Competing Interests: The authors declare no conflict of interest. (Copyright © 2017 the Author(s). Published by PNAS.)
Databáze:	MEDLINE
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