Banse Early Career Scientist Seminar

Wednesday, March 06, 03:30 PM to 04:30 PM PST

Ocean Sciences Building (OSB), Room 425 with tea and cookies to follow

Sophie Nuber, UW Oceanography

Title: Mid Pleistocene Climate Transition Forced by a Combination of CO2 and Ocean Climate Dynamics

Abstract: The Mid-Pleistocene transition (MPT) is a period of major unexplained increases in glacial ice volume leading to changes in the shape, periodicity and amplitude of glacial-interglacial climate cycles. Late Pleistocene glacial cycles are largely shaped by a feedback combination of ice volume with atmospheric CO2. As such, low glacial CO2 values aid the development of extreme glacial maxima causing glacial periods to sustain multiple insolation peaks. Yet, little is known about the relationship between pCO2 and ice volume during the MPT, as data has been sparse. Here, we present the first glacial-interglacial resolving d11B-derived atmospheric CO2 composite across the MPT. Prior to the MPT, pCO2 and ice volume closely follow integrated summer insolation at 65°N with a strong 41kyr cyclicity. We find that pCO2 and ice volume diverge in-tandem from external forcing for the first time during early-MPT glacials, a signature of Late Pleistocene climate cycles. The prolonged low glacial pCO2 values during early MPT glacials occur in line with saltier Atlantic deep waters enriched in d13C which we interpret to be of southern origin and linked to a reorganisation of deep water formation around Antarctica. Additional ice sheet modelling shows that the 100kyr cycle emerges as a result of the interplay between CO2 and ocean circulation, whereby a threshold in interglacial CO2 values is crossed which causes the extension of ice in the following glacial, while ocean circulation enhances the northward heat transport to sustain ice sheets in the north.