Atmospheric Carbon Dioxide Concentration Across the Mid-Pleistocene Transition

Abstract

During the Mid-Pleistocene Transition (MPT; 1,200-800 kya), Earth's orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO 2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO 2 data to show that the glacial to interglacial CO 2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO 2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO 2-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 CO 2 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. boron isotopes | MPT | geochemistry | carbon dioxide | paleoclimate

Pleistocene sea-surface temperature evolution: Early cooling, delayed glacial intensification, and implications for the mid-Pleistocene climate transition

“…5 reconstructions do not show a long-term decline during the Pleistocene, but suggest that glacial values prior to ~1 Ma were 30±30 atm higher than the late Pleistocene (Hönisch et al, 2009). In contrast, estimated interglacial pCO 2 values before the MPT are statistically the same as those of the late Pleistocene, with a temporary reduction in interglacial pCO 2 between 1 and 0.6 Ma (Hönisch et al, 2009).…”

Winners always win: growth of a wide range of plant species from low to future high CO2

“…2009) but will likely experience a doubling of CO 2 in the next 80 years. This is a short period for evolutionary change especially given the rapid rise from 280 ppm to current ~400 ppm CO 2 since the start of the industrial revolution.…”

“…At an evolutionary timescale, the variation in CO 2 has been even larger, ranging from 3000 ppm in the Devonian down to 180 ppm during the Pleistocene Ice Age (Royer 2006; Hönisch et al. 2009). It is only after the industrial revolution that CO 2 levels started to rise from 280 ppm to the 400 ppm we have today.…”

The role of orbital forcing in the Early Middle Pleistocene Transition

“…Though the data is sparse it seems to indicate a drop in both the interglacial level of carbon dioxide from ~290 ppm to ~ 260 ppm and the glacial level from 220 ppm to 180 ppm. At the MBE the glacial level remains the same but the interglacial level rises to it pre-EMPT level of 290 ppm (Hönisch et al, 2009). Hence the cooling trend through the EMPT could have been driven by the observed reduced concentration of greenhouse gases in the atmosphere.…”

“…It has been suggested that the critical size of the Northern Hemisphere ice sheets may have been influenced by changing levels of greenhouse gases (Clark et al, 2006;Crowley and Hyde, 2008;DeConto et al, 2008). The atmospheric carbon dioxide reconstruction by Hönisch et al (2009) shows significant changes at the EMPT and the Mid-Brunhes Event (MBE) see Figure 7. Though the data is sparse it seems to indicate a drop in both the interglacial level of carbon dioxide from ~290 ppm to ~ 260 ppm and the glacial level from 220 ppm to 180 ppm.…”