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, and Paul A. Wilson
PNAS December 12, 2017 114 (50) 13114-13119; first published November 27, 2017 https://doi.org/10.1073/pnas.1702143114

  1. Edited by Maureen E. Raymo, Lamont–Doherty Earth Observatory of Columbia University, Palisades, NY, and approved September 7, 2017 (received for review February 9, 2017)

Significance

Conflicting sets of hypotheses highlight either the role of ice sheets or atmospheric carbon dioxide (CO2) in causing the increase in duration and severity of ice age cycles ∼1 Mya during the Mid-Pleistocene Transition (MPT). We document early MPT CO2 cycles that were smaller than during recent ice age cycles. Using model simulations, we attribute this to post-MPT increase in glacial-stage dustiness and its effect on Southern Ocean productivity. Detailed analysis reveals the importance of CO2 climate forcing as a powerful positive feedback that magnified MPT climate change originally triggered by a change in ice sheet dynamics. These findings offer insights into the close coupling of climate, oceans, and ice sheets within the Earth System.

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.

Footnotes

  • ↵1T.B.C. and M.P.H. contributed equally to this work.

  • ↵2To whom correspondence may be addressed. Email: T.chalk{at}noc.soton.ac.uk or M.P.Hain{at}soton.ac.uk.

  • Author contributions: T.B.C., M.P.H., G.L.F., E.J.R., A.P.H., G.H.H., S.L.J., A.M.-G., R.D.P., and P.A.W. designed research; T.B.C., M.P.H., M.P.S.B., and S.G.C. performed research; T.B.C., M.P.H., G.L.F., E.J.R., P.F.S., S.G.C., H.P., and P.A.W. analyzed data; and T.B.C. and M.P.H. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • Data deposition: The data reported in this paper have been deposited in the Pangaea database (https://doi.pangaea.de/10.1594/PANGAEA.882551).

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1702143114/-/DCSupplemental.

  1. Thomas B. Chalka,b,1,2,
  2. Mathis P. Haina,1,2,
  3. Gavin L. Fostera,
  4. Eelco J. Rohlinga,c,
  5. Philip F. Sextond,
  6. Marcus P. S. Badgerd,e,
  7. Soraya G. Cherrya,
  8. Adam P. Hasenfratzf,
  9. Gerald H. Haugg,
  10. Samuel L. Jaccardh,i,
  11. Alfredo Martínez-Garcíag,
  12. Heiko Pälikea,j,
  13. Richard D. Pancoste, and
  14. Paul A. Wilsona
  1. aOcean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom;
  2. bDepartment of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543;
  3. cResearch School of Earth Sciences, The Australian National University, Canberra 2601, Australia;
  4. dSchool of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom;
  5. eOrganic Geochemistry Unit, School of Chemistry, The Cabot Institute, University of Bristol, Bristol BS8 1TS, United Kingdom;
  6. fGeologisches Institut, Eidgenössische Technische Hochschule Zürich, 8092 Zürich, Switzerland;
  7. gMax Planck Institut für Chemie, 55128 Mainz, Germany;
  8. hInstitute of Geological Sciences, University of Bern, 3012 Bern, Switzerland;
  9. iOeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland;
  10. jCenter for Marine Environmental Sciences (MARUM), University of Bremen, 28359 Bremen, Germany

  1. Edited by Maureen E. Raymo, Lamont–Doherty Earth Observatory of Columbia University, Palisades, NY, and approved September 7, 2017 (received for review February 9, 2017)

Significance

Conflicting sets of hypotheses highlight either the role of ice sheets or atmospheric carbon dioxide (CO2) in causing the increase in duration and severity of ice age cycles ∼1 Mya during the Mid-Pleistocene Transition (MPT). We document early MPT CO2 cycles that were smaller than during recent ice age cycles. Using model simulations, we attribute this to post-MPT increase in glacial-stage dustiness and its effect on Southern Ocean productivity. Detailed analysis reveals the importance of CO2 climate forcing as a powerful positive feedback that magnified MPT climate change originally triggered by a change in ice sheet dynamics. These findings offer insights into the close coupling of climate, oceans, and ice sheets within the Earth System.

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.

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

Footnotes

  • ↵1T.B.C. and M.P.H. contributed equally to this work.

  • ↵2To whom correspondence may be addressed. Email: T.chalk{at}noc.soton.ac.uk or M.P.Hain{at}soton.ac.uk.

  • Author contributions: T.B.C., M.P.H., G.L.F., E.J.R., A.P.H., G.H.H., S.L.J., A.M.-G., R.D.P., and P.A.W. designed research; T.B.C., M.P.H., M.P.S.B., and S.G.C. performed research; T.B.C., M.P.H., G.L.F., E.J.R., P.F.S., S.G.C., H.P., and P.A.W. analyzed data; and T.B.C. and M.P.H. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • Data deposition: The data reported in this paper have been deposited in the Pangaea database (https://doi.pangaea.de/10.1594/PANGAEA.882551).

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1702143114/-/DCSupplemental.

View Full Text
View Full Text
Back to top
Article Alerts
Email Article
Citation Tools
Request Permissions
Causes of ice age intensification across the MPT
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
Proceedings of the National Academy of Sciences Dec 2017, 114 (50) 13114-13119; DOI: 10.1073/pnas.1702143114
del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Facebook logo Google logo Mendeley logo
Proceedings of the National Academy of Sciences: 116 (34)
Current Issue

Submit

Article Classifications

Jump to section

You May Also be Interested in

The ammonite in Burmese amber. Image courtesy of Bo Wang.
Rare instance of ammonite preserved in amber
Researchers report a marine ammonite from the Cretaceous Period preserved in Burmese amber from Myanmar, and the rare specimen in amber warrants exploration of the possibly exceptional circumstances of its fossilization.
Image courtesy of Bo Wang.
Virus. Image courtesy of Pixabay/qimono.
How dry air increases susceptibility to influenza
Exposure to low humidity makes mice infected with influenza more susceptible to severe disease by impairing airway tissue repair and innate antiviral defense, suggesting that controlling humidity may help curb influenza during winter.
Image courtesy of Pixabay/qimono.

Similar Articles