Professor Gavin Foster
Peel Lecture Theatre, Geographical Sciences
Please note this event is only open to University of Bristol staff and students.
Professor Gavin Foster - Causes of ice age intensification across the Mid-Pleistocene Transition
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 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.
Gavin Foster is a Professor of Isotope Geochemistry at the University of Southampton.