Scatter plot of the different CO 2 proxies as a function of the reconstructed temperature, which is derived from the benthic δ 18 O record as shown in Fig. 1. Only records with filled symbols δ 11 B h (Hönisch et al., 2009), B/Ca (Tripati et al., 2009), alkenones+ δ 11 B s (Seki et al., 2010), stomata data (Kürschner et al., 1996, 2008; Retallack 2009), and the ice-core record (Petit et al., 1999; Siegenthaler et al., 2005; Lüthi et al., 2008) are used for further analysis. For reasons of transparency CO 2 is plotted in ppmv. If CO 2 would be plotted as ln(CO 2 /CO 2 , ref ) a similar picture emerges. The latter is physically more consistent as it takes the saturation of the absorption bands into account.

Scatter plot of the different CO 2 proxies as a function of the reconstructed temperature, which is derived from the benthic δ 18 O record as shown in Fig. 1. Only records with filled symbols δ 11 B h (Hönisch et al., 2009), B/Ca (Tripati et al., 2009), alkenones+ δ 11 B s (Seki et al., 2010), stomata data (Kürschner et al., 1996, 2008; Retallack 2009), and the ice-core record (Petit et al., 1999; Siegenthaler et al., 2005; Lüthi et al., 2008) are used for further analysis. For reasons of transparency CO 2 is plotted in ppmv. If CO 2 would be plotted as ln(CO 2 /CO 2 , ref ) a similar picture emerges. The latter is physically more consistent as it takes the saturation of the absorption bands into account.

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The gradual cooling of the climate during the Cenozoic has generally been attributed to a decrease in CO2 concentration in the atmosphere. The lack of transient climate models and, in particular, the lack of high-resolution proxy records of CO2, beyond the ice-core record prohibit, however, a full understanding of, for example, the inception of the...

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... δ 18 O record offers a framework to do so. We use the modelled temperature as a tool to select mu- tually consistent CO 2 records by assuming that there is a re- lation between CO 2 and T NH , which is comparable to the relation found in ice cores. In fact, this is justified as sev- eral independent proxies do show a similar linear relation (Fig. 4). Different methodologies may explain why the δ 11 B h (δ 11 B from Hönisch et al., 2009) is more consistent with the ice cores CO 2 data then the δ 11 B p (δ 11 around glacial and interglacial extremes, which was not done by Pearson and Palmer (2000). In addition, it has been ar- gued that the Pearson and Palmer (2000) data need to be ...
Context 2
... and interglacial extremes, which was not done by Pearson and Palmer (2000). In addition, it has been ar- gued that the Pearson and Palmer (2000) data need to be re- jected for reasons related to diagenesis, use of incorrect frac- tionation factors, and poor modelling of seawater alkalinity and δ 11 B ( Foster et al., 2006). The comparison in Fig. 4 reveals that the CO 2 estimates derived from the ice cores, B/Ca, stomata, δ 11 B h and the combination of alkenones and δ 11 B s (δ 11 B from Seki et al., 2010) are mutually consistent, because they reveal similar slopes, whereas the δ 11 B p , and alkenones-derived CO 2 estimates do not show a consistency with the ice-core record. ...

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... Similar results were reported for the Chinese alligator (Wan et al., 2013) and elapid snakes (Ludington & Sanders, 2020). Marine reptiles also showed a decline in N e size over the last glacial period (Fitak & Johnsen, 2018;Kishida et al., 2020;Ludington & Sanders, 2020) suggesting that global climatic events including a generalised decrease in temperature ( Van de Wal, De Boer, Lourens, Köhler, & Bintanja, 2011), may have had major demographic consequences for ectothermic species. A reduction in temperature could have played only a minor role in Komodo dragon N e reduction. ...
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... Furthermore, in an additional step these inverse modeling approaches have also been used to reconstruct the temporal evolution of atmospheric CO 2 across the Pleistocene (Berends et al., 2021;Stap et al., 2018;van de Wal et al., 2011). Van de Wal et al. (2011) calculated CO 2 in post-processing as function of temperature change, while it was directly included in the inverse approach in the other studies. Although these inverse modeling studies are, necessarily, based on simplifications of complex physical processes (e.g., a linearized relation between surface temperatures and deep-sea temperatures, neglecting secondary influences on benthic δ 18 O such as changes in ocean pH, etc.; Modestou et al., 2020), their results generally show a good agreement with proxy records of global mean temperature, ice surface temperature, and ice core CO 2 (Berends et al., 2021). ...
... An advantage of the approach is that ice volume, temperature, and CO 2 are reconstructed simultaneously, allowing lead-lag relations to be studied without the age model uncertainties present in independent proxy reconstructions. The reconstructed contributions to the benthic δ 18 O signal from changes in ice volume and deep-water temperature by Berends et al. (2021) and de Boer et al. (2014) are shown in Figure 6 (while van de Wal et al. (2011) used the same inverse modeling approach, they did not report the separate δ 18 O contributions). ...
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... The CO 2 reconstruction for the past 800 kyr is compared to the EPICA Dome C ice-core record (Bereiter et al., 2015) in Fig. 6, as well as to several different model reconstructions and proxy-based reconstructions. The three other modelbased reconstructions shown were created by decoupling the benthic δ 18 O signal using a 1-D ice-sheet model (van de Wal et al., 2011;Stap et al., 2017), or by using an insolationforced, fully coupled ice-sheet-climate-carbon-cycle model (Willeit et al., 2019). The geological proxies are either based on alkenones (Seki et al., 2010;Badger et al., 2013;Zhang et al., 2013) or δ 11 B ratios Seki et al., 2010;Bartoli et al., 2011;Martínez-Botí et al., 2015;Stap et al., 2016;Chalk et al., 2017;Dyez et al., 2018;Sosdian et al., 2018) derived from benthic foraminifera, or based on stomata (Kürschner et al., 1996;Stults et al., 2011;Bai et al., 2015;Hu et al., 2015). ...
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... This interpretation of little long-term change in the temperature of glacial maxima across the MPT agrees with a 29,48,49 . e Atmospheric CO 2 and its radiative forcing of ΔR ½CO 2 based on ice cores 37 , Allan Hills Blue Ice 34 , various marine proxies (δ 11 B from either T sacculifer 10,12,57 or G ruber 11,58-61 , alkenones 58,62,63 ) paleosol 33 , model simulation 9 and data-based reconstruction 38,39 . Error bars show 1σ uncertainty. ...
... CO 2 reconstructions seemed to some degree to depend on the underlying proxy 12 (Fig. 4d). Simulated CO 2 shows specifically small glacial/interglacial amplitudes of only 20-40 ppm early in the Quaternary 9 , not yet contained in individual proxy-data sets or in the model-based synthesis of previous approaches 38,39 . Simulation experiments 40 have shown that glacial/interglacial transitions during the late Quaternary also occur when CO 2 is kept fixed, although no lengthening of the glacial cycles has then been observed, pointing towards a central role of a carbon cycle feedback during the MPT. ...
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Article
Steep topography, a tropical climate, and mafic lithologies contribute to efficient chemical weathering and carbon sequestration in the Southeast Asian islands. Ongoing arc-continent collision between the Sunda-Banda arc system and Australia has increased the area of subaerially exposed land in the region since the mid-Miocene. Concurrently, Earth's climate has cooled since the Miocene Climatic Optimum, leading to growth of the Antarctic ice sheet and the onset of Northern Hemisphere glaciation. We seek to evaluate the hypothesis that the emergence of the Southeast Asian islands played a significant role in driving this cooling trend through increasing global weatherability. To do so, we have compiled paleoshoreline data and incorporated them into GEOCLIM, which couples a global climate model to a silicate weathering model with spatially resolved lithology. We find that without the increase in area of the Southeast Asian islands over the Neogene, atmospheric pCO2 would have been significantly higher than preindustrial values, remaining above the levels necessary for initiating Northern Hemisphere ice sheets.
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