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

• Published in: Earth and Planetary Science Letters
• Main Authors: Stap, Lennert B., de Boer, Bas, Ziegler, Martin, Bintanja, Richard, Lourens, Lucas J., van de Wal, Roderik S.W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Carbon dioxide; Global climate; Global ice volume; Plio-Pleistocene; Proxy data; Sea level; /dk/atira/pure/sustainabledevelopmentgoals/climate_action; name=SDG 13 - Climate Action; /dk/atira/pure/sustainabledevelopmentgoals/life_below_water; name=SDG 14 - Life Below Water; Antarctic; East Antarctica; Antarc*; Antarctica; ice core; Ice Sheet
• Online Access: https://research.vu.nl/en/publications/33f0db0c-3f1d-4b02-bde6-6b7cd8de93c4; https://doi.org/10.1016/j.epsl.2016.01.022; https://hdl.handle.net/1871.1/33f0db0c-3f1d-4b02-bde6-6b7cd8de93c4; http://www.scopus.com/inward/record.url?scp=84961332596&partnerID=8YFLogxK; http://www.scopus.com/inward/citedby.url?scp=84961332596&partnerID=8YFLogxK

During the past five million yrs, benthic δ 18 O records indicate a large range of climates, from warmer than today during the Pliocene Warm Period to considerably colder during glacials. Antarctic ice cores have revealed Pleistocene glacial-interglacial CO 2 variability of 60-100 ppm, while sea level fluctuations of typically 125 m are documented by proxy data. However, in the pre-ice core period, CO 2 and sea level proxy data are scarce and there is disagreement between different proxies and different records of the same proxy. This hampers comprehensive understanding of the long-term relations between CO 2 , sea level and climate. Here, we drive a coupled climate-ice sheet model over the past five million years, inversely forced by a stacked benthic δ 18 O record. We obtain continuous simulations of benthic δ 18 O, sea level and CO 2 that are mutually consistent. Our model shows CO 2 concentrations of 300 to 470 ppm during the Early Pliocene. Furthermore, we simulate strong CO 2 variability during the Pliocene and Early Pleistocene. These features are broadly supported by existing and new δ 11 B-based proxy CO 2 data, but less by alkenone-based records. The simulated concentrations and variations therein are larger than expected from global mean temperature changes. Our findings thus suggest a smaller Earth System Sensitivity than previously thought. This is explained by a more restricted role of land ice variability in the Pliocene. The largest uncertainty in our simulation arises from the mass balance formulation of East Antarctica, which governs the variability in sea level, but only modestly affects the modeled CO 2 concentrations.