Evolution of Ocean Temperature and Ice Volume Through the Mid-Pleistocene Climate Transition

Abstract

Earth's climate underwent a fundamental change between 1250 and 700 thousand years ago, the mid-Pleistocene transition (MPT), when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing. Over this time, an increase occurred in the amplitude of change of deep-ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature. We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume 900 thousand years ago. We see no evidence of a pattern of gradual cooling, but near-freezing temperatures occur at every glacial maximum.

Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

“…The PGMeLGM value of Dz estimated from d sw (Elderfield et al, 2012) appears less well defined and less conclusive than that estimated from the other sea-level records (Table 2). Ice-volume/ sea-level reconstructions from seawater d 18 O records have so far either assumed a temporally invariant relationship, or one in which ice became isotopically more negative with increasing ice volume within a glacial cycle (e.g., Duplessy et al, 2002;Waelbroeck et al, 2002;Bintanja et al, 2005;Siddall et al, 2010;de Boer et al, 2014 LGM values that are identical within uncertainties (Table 4).…”

“…Ice-sheet nucleation may, in addition, depend on chaotic aspects of the weather/climate system; for example, successive winters with heavy snowfall may e almost randomly e cause some locations to receive an initial snow cover with enough volume and albedo feedback to ensure its survival and subsequent growth potential (e.g., Oglesby, 1990). Finally, modelling studies (e.g., Abe-Ouchi et al, 2013) indicate that glacial culminations like the PGM and LGM reflect the outcome of temporal developments in forcings and feedbacks through the preceding glacial cycle that include insolation (e.g., Laskar et al, 2004;Colleoni et al, 2011), CO 2 and CH 4 concentrations (Monnin et al, 2001;Loulergue et al, 2008; Waelbroeck et al, 2002;Rohling et al, 2009Rohling et al, , 2014Elderfield et al, 2012;Grant et al, 2014), and also in state variables such as surface and deep-sea temperature (e.g., Stenni et al, 2010;Elderfield et al, 2012;Parrenin et al, 2013;Rohling et al, 2012Rohling et al, , 2014Martínez-Botí et al, 2015;Snyder, 2016a,b). Climate simulations by Colleoni et al (2014) suggest that orbital and greenhouse-gas changes for the penultimate glacial cycle were more favourable for glacial inception over Eurasia than over North America, relative to the last glacial cycle.…”

“…The LGM gap in the Red Sea data-series represents the prominent LGM aplanktonic zone discussed in the text. c. Results from a and b compared with SW Pacific deep-sea d sw sea-level estimates with 1s uncertainties (Elderfield et al, 2012), and its probabilistic assessment . d. As c, but compared with fossil coral positions (Zcp) (Hibbert et al, 2016) with 95% uncertainties.…”

“…The first two are (near) continuous relative sea-level records derived from surface-water d 18 O residence-time effects in the highly evaporative Red Sea and Mediterranean Sea (Siddall et al, 2003;Rohling et al, 2014). The third source is a (near) continuous time-series of past ice volume/ sea level from deep-sea seawater d 18 O, hereafter named d sw (e.g., Martin et al, 2002;Sosdian and Rosenthal, 2009;Elderfield et al, 2012). The fourth source for our assessment of a PGMeLGM sealevel offset concerns fossil coral position data (Z cp ) from a comprehensive database that has been harmonised in terms of dating and uplift-correction protocols (Hibbert et al, 2016).…”

“…Martin et al, 2002;Elderfield et al, 2012). These are derived from benthic foraminiferal carbonate d 18 O data (d c ) that are corrected for temperature changes using Mg/Ca analyses of the same benthic foraminifera (Martin et al, 2002;Sosdian and Rosenthal, 2009;Elderfield et al, 2010Elderfield et al, , 2012 (Elderfield et al, 2012). Specifically, we use a probabilistic assessment of that record, which highlights the overall signal structure, and accounts for both chronological and sea-level uncertainties (Fig.…”