Causes of ice age intensification across the Mid-Pleistocene Transition


25 April 2018, 1.00 PM - 25 April 2018, 2.00 PM

Peel Lecture theatre, School of Geographical Sciences, University of Bristol

A Geography Departmental Seminar by Professor Gavin Foster, University of Southampton.

Please note this event is only open to University of Bristol staff and students.


During the Mid-Pleistocene Transition (MPT) around 1 million years ago, Earth’s orbitally paced ice age cycles intensified, lengthened from ~40 kyr to ~100 kyr and become distinctly asymmetric.  A number of conflicting hypotheses exist for this event and all invoke either a role for changing ice dynamics or a decrease in atmospheric carbon dioxide.  Here I will present new high resolution d11B-based CO2 estimates from early in the MPT to show that the glacial to interglacial CO2 difference increased from ~43 to ~75 ppm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modelling we are able to attribute this decline primarily to the initiation of substantive dust-borne Fe-fertilisation of the Southern Ocean during post-MPT 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 CO2change 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.


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