Causes of ice-age intensification across the Mid-Pleistocene Transition, insights from a new boron isotope CO2 record

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• Thomas Chalk, National Oceanography Centre, Southampton
• Thursday 09 March 2017, 17:30-18:30
• Latimer Room (Old Court), Clare College, Trinity Lane.

If you have a question about this talk, please contact Dr Rachael Rhodes.

During the Mid-Pleistocene Transition (MPT; 1200–800 thousand years ago, kyrs) Earth’s orbitally paced ice-age cycles intensified, lengthened from _{40 to} 100 kyrs, 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 demonstrate that the glacial-to-interglacial CO2 difference increased from _{43 to} 75 µatm across the MPT , mainly due to lower CO2 levels during glacials. Through carbon-cycle modelling, 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 two-fold 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. We argue that neither ice-sheet dynamics nor CO2 change in isolation can explain the MPT . Instead, we infer that the MPT 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.

This talk is part of the Quaternary Discussion Group (QDG).

This talk is part of the Quaternary Discussion Group (QDG) series.

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