CO 2 over the past 5 million years: Continuous simulation and new δ 11 B-based proxy data

Stap, Lennert B.; Boer, Bas de; Ziegler, Martin; Bintanja, Richard; Lourens, Lucas Joost; Wal, R. S. W. van de

doi:10.1016/j.epsl.2016.01.022

Cited by 92 publications

(131 citation statements)

References 48 publications

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“…The record of Lisiecki and Raymo (2005) was used to force the 5 Myr run after initialising the model for 100 kyr with 430 ppm CO 2 . This run served as a reference run before in Stap et al (2016a). When we compare the The starting point of the simulation at 450 ppm CO 2 is marked by an S, and the consequent evolution for both runs is marked by coloured arrows.…”

Section: Hysteresismentioning

confidence: 99%

“…where CO 2 is the mean CO 2 concentration of the preceding 15 kyr, and c is a strength-determining parameter (Stap et al, 2016a). For the observed benthic δ 18 O values we use stacked records (Lisiecki and Raymo, 2005;Zachos et al, 2008), which effectively serve as model input.…”

Section: Modelmentioning

confidence: 99%

“…Originally, the 5 Myr run was calibrated to an Antarctic ice core proxy CO 2 record (Petit et al, 1999;Siegenthaler et al, 2005;Lüthi et al, 2008) over the past 800 kyr (Stap et al, 2016a). It shows negligible bias (−3.9 ppm) to that record.…”

Section: Retuning: New Reference Simulationmentioning

confidence: 99%

“…The gain factor γ is set to 0.28 ‰ K −1 , taken from a paleotemperature equation (Duplessy et al, 2002). The coupled model is forced by insolation data (Laskar et al, 2004) and an inverse routine, which yields CO 2 concentrations from the difference between the modelled benthic δ 18 O value and an observed value an output timestep later (Stap et al, 2016a):…”

Section: Modelmentioning

confidence: 99%

“…Furthermore, instead of annual mean and globally uniform temperature perturbations to present-day climate, seasonal meridional temperature distributions were used to force the different ice sheets. In a subsequent study, the inverse routine was transformed to yield CO 2 concentrations using the benthic δ 18 O as input, making CO 2 a prognostic variable (Stap et al, 2016a). The resulting values were used to force the coupled model over the past 5 Myr.…”

Section: Introductionmentioning

confidence: 99%

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The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

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Abstract. Since the inception of the Antarctic ice sheet at the Eocene-Oligocene transition ( ∼ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice-albedo and surface-height-temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO 2 . Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO 2 and temperature is subject to hysteresis. When the climate cools from very high CO 2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO 2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO 2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO 2 , temperature, ice-volume-equivalent sea level, and benthic δ 18 O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet-climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice-albedo and surfaceheight-temperature feedbacks. We find that ice volume variability has a strong enhancing effect on atmospheric temperature changes, particularly in the regions where the ice sheets are located. As a result, polar amplification in the Northern Hemisphere decreases towards warmer climates as there is little land ice left to melt. Conversely, decay of the Antarctic ice sheet increases polar amplification in the Southern Hemisphere in the high-CO 2 regime. Our results also show that in cooler climates than the pre-industrial, the ice-albedo feedback predominates the surface-heighttemperature feedback, while in warmer climates they are more equal in strength.

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Section: Hysteresismentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Section: Retuning: New Reference Simulationmentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

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Low‐frequency Pliocene climate variability in the eastern Nordic Seas

et al. 2016

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The MMCO‐EOT conundrum: Same benthic δ¹⁸O, different CO₂

et al. 2016

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Knowledge on climate change during the Cenozoic largely stems from benthic δ18O records, which document combined effects of deep‐sea temperature and ice volume. Information on CO2 is expanding but remains uncertain and intermittent. Attempts to reconcile δ18O, sea level, and CO2 by studying proxy data suffer from paucity of data and apparent inconsistencies among different records. One outstanding issue is the difference suggested by proxy CO2 data between the Eocene‐Oligocene boundary (EOT) and the Middle‐Miocene Climatic Optimum (MMCO), while similar levels of δ18O are shown during these times. This conundrum implies changing relations between δ18O, CO2, and temperature over time. Here we use a coupled climate‐ice sheet model, forced by two different benthic δ18O records, to obtain continuous and mutually consistent records of δ18O, CO2, temperature, and sea level over the period 38 to 10 Myr ago. We show that the different CO2 levels between the EOT and MMCO can be explained neither by the standard configuration of our model nor by altering the uncertain ablation parametrization on the East Antarctic Ice Sheet. However, we offer an explanation for the MMCO‐EOT conundrum by considering erosion and/or tectonic movement of Antarctica, letting the topography evolve over time. A decreasing height of the Antarctic continent leads to higher surface temperatures, reducing the CO2 needed to maintain the same ice volume. This also leads to an increasing contribution of ice volume to the δ18O signal. This result is, however, dependent on how the topographic changes are implemented in our ice sheet model.

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CO 2 over the past 5 million years: Continuous simulation and new δ 11 B-based proxy data

Cited by 92 publications

References 48 publications

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

Low‐frequency Pliocene climate variability in the eastern Nordic Seas

The MMCO‐EOT conundrum: Same benthic δ¹⁸O, different CO₂

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CO 2 over the past 5 million years: Continuous simulation and new δ 11 B-based proxy data

Cited by 92 publications

References 48 publications

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

Low‐frequency Pliocene climate variability in the eastern Nordic Seas

The MMCO‐EOT conundrum: Same benthic δ18O, different CO2

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The MMCO‐EOT conundrum: Same benthic δ¹⁸O, different CO₂