Mid-Pleistocene transition in glacial cycles explained by declining CO ₂ and regolith removal

Abstract

Variations in Earth’s orbit pace the glacial-interglacial cycles of the Quaternary, but the mechanisms that transform regional and seasonal variations in solar insolation into glacial-interglacial cycles are still elusive. Here, we present transient simulations of coevolution of climate, ice sheets, and carbon cycle over the past 3 million years. We show that a gradual lowering of atmospheric CO2and regolith removal are essential to reproduce the evolution of climate variability over the Quaternary. The long-term CO2decrease leads to the initiation of Northern Hemisphere glaciation and an increase in the amplitude of glacial-interglacial variations, while the combined effect of CO2decline and regolith removal controls the timing of the transition from a 41,000- to 100,000-year world. Our results suggest that the current CO2concentration is unprecedented over the past 3 million years and that global temperature never exceeded the preindustrial value by more than 2°C during the Quaternary.

Plio‐Pleistocene Hemispheric (A)Symmetries in the Northern and Southern Hemisphere Midlatitudes

“…Multiple studies have invoked a carbon cycle change to explain the origin of the MPT, for example, via iron fertilization in the Southern Ocean (Martínez-Garcia et al, 2011), ocean overturning circulation changes leading to an increase in deep sea carbon storage (Farmer et al, 2019;Lear et al, 2016;Pena & Goldstein, 2014) or enhanced silicate weathering (Clark et al, 2006). Such a carbon cycle change could have operated with or without the additional influence of a change in ice sheet dynamics, by either regolith removal (Clark & Pollard, 1998) or phase locking of the Northern and Southern Hemisphere ice sheets (Raymo et al, 2006), though recent modeling results support the interpretation that a carbon cycle change acted in tandem with evolving ice sheet dynamics in order to trigger the transition to the 100-kyr world (Chalk et al, 2017;Willeit et al, 2019).…”

“…A second major climate shift, the mid-Pleistocene transition (MPT;~0.7-1.25 Ma), is defined by what appears to be a globally synchronous switch from dominant 41-to~100-kyr climate cycles, for which the ultimate cause is still unknown (e.g., Chalk et al, 2017;Clark & Pollard, 1998;Farmer et al, 2019;Pena & Goldstein, 2014;Raymo et al, 2006;Willeit et al, 2019). Secular-scale and orbital-scale changes in greenhouse gas concentrations have been invoked to explain both the LPT (e.g., Lunt et al, 2008;Martínez-Botí et al, 2015;Seki et al, 2010) and the MPT (Chalk et al, 2017;Farmer et al, 2019;Hönisch et al, 2009;Willeit et al, 2019), the latter of which may have also involved critical changes in ice sheet dynamics in either the Northern (Clark & Pollard, 1998) or Southern (Raymo et al, 2006) Hemisphere cryosphere. Given important questions regarding the hemispheric symmetry of climate evolution over these profound transitions, as well as the critical role of the Southern Hemisphere in carbon cycling, better characterization of Southern Hemisphere climate evolution over the Plio-Pleistocene is essential in improving our understanding of the mechanisms behind the significant climate changes that occurred over this interval.…”

Interglacial Paleoclimate in the Arctic

“…Understanding high‐latitude cryospheric and climate variability during MIS 11 helps determine the sensitivity of Greenland and Antarctic Ice Sheets to atmospheric CO 2 (Jouzel et al, ); the role of orbitally driven insolation (Rohling et al, ; Willeit et al, ; Yin & Berger, ); the phenomenon of Arctic Amplification, that is, amplified warming in Arctic regions due to sea ice loss and other processes, relative to global mean temperature (Cronin et al, ); and the potential for abrupt, millennial scale events during warm climate intervals (McManus et al, ). Importantly, MIS 11 is also relevant for understanding the evolution of climate during the Holocene interglacial, specifically for distinguishing natural climate variability from anthropogenic influence on climate (Palumbo et al, ; Ruddiman, ).…”

Modeling perspectives on the mid-Pleistocene transition

“…We have used the simplified Earth system model CLIMbEr-2 to elucidate the drivers behind the transitions in glacial cycles of the Quaternary (Willeit et al 2019). besides the ocean and atmosphere, the model includes a dynamic vegetation module, interactive ice sheets for the Northern Hemisphere, and a fully coupled global carbon cycle, allowing us to interactively simulate atmospheric CO 2 (Ganopolski and brovkin 2017).…”