7.5-4.0 Ma reconstructed CO2 with paleosol-CO2 method in Chinese Loess Plateau deposits (Jiaxian and Shilou sections)

We generate a high-resolution, highly variable terrestrial CO₂ record spanning 7.5–4.0 Ma by applying a machine learning-based multi-proxy paleosol-CO₂ inversion to Chinese Loess Plateau deposits (Jiaxian and Shilou sections).Data Sources:Inorganic Isotopes, Elements & Grain Size: The carbonate stable isotopes (d13Cc, d18Oc), elemental concentrations (aFe, aSi, aAl, fFe), grain size (D), and magnetic susceptibility (Xlf) were measured in this study across both sections.Organic Carbon Isotopes (d13Co):Jiaxian Section: Values are interpolated from the high-resolution nodule organic isotope record published by Gallagher et al. (2021).Shilou Section: Values were measured directly in this study on decarbonated paleosol samples.Formation Temperature (Temperature): Interpolated from soil temperature records derived from carbonate nodule clumped isotopes (Δ47) (Da, 2025).Atmospheric Carbon Isotopes (d13Ca): Estimated from high-resolution marine carbonate records (Tipple et al., 2010).Atmospheric CO₂ & Sz Reconstructions: Soil-respired CO₂ (Sz) was predicted using our optimized Gradient Boosting machine learning model, which was then inverted with the isotopic mixing ratio (R) to reconstruct atmospheric CO₂.Column Definitions and Units:Sample ID: Unique identifier for each Red Clay paleosol sample.Depth(m): Stratigraphic depth of the sample (meters).Age (Ma): Estimated age of the sample (Million years ago).Xlf: Low-frequency magnetic susceptibility. (Xlf_std: standard deviation).Ampl 46: Signal amplitude for mass 46 during isotope ratio mass spectrometry.d13Cc, d18Oc: Carbon and oxygen isotopic composition of pedogenic carbonate (‰, VPDB).d13Cc_std, d18Oc_std: 1σ uncertainties of the carbonate isotopic measurements.d13Cc_n, d18Oc_n: Number of replicate measurements for carbonate isotopes.d13Co: Carbon isotopic composition of soil organic matter (‰, VPDB).d13Co_std: 1σ uncertainty of the organic carbon isotopic composition.Temperature: Estimated formation temperature of pedogenic carbonates (°C).Temperature_std: 1σ uncertainty of the formation temperature (°C).d13Ca: Estimated carbon isotopic composition of atmospheric CO₂ (‰, VPDB).d13Ca_std: 1σ uncertainty of atmospheric CO₂ isotopic composition.aAl, aFe, aSi: Amorphous aluminum, iron, and silicon concentrations (mass %, quantified by their corresponding oxides).fFe: Free iron oxides concentration (mass %, quantified by its corresponding oxide).[Element]_std: 1σ standard deviation for the respective element concentration.[Element]_sem: Standard error of the mean for the respective element concentration.[Element]_n: Number of replicate measurements for the element extraction.n_measurements_max: Maximum number of replicates among the elemental measurements.aFe/aSi, aFe/aAl, aSi/aAl, aFe/fFe, aSi/fFe, aAl/fFe: Calculated stoichiometric ratios of the respective amorphous/free element concentrations.[Ratio]_std: 1σ uncertainties of the elemental ratios, propagated using a Taylor expansion series.D: Volume weighted mean grain size, D[4, 3] (μm).D_std: 1σ uncertainty of the grain size measurement (μm).R: Calculated mixing ratio of atmospheric CO₂ versus soil-respired CO₂.R_std: 1σ uncertainty of the mixing ratio R.R_90_low, R_90_high: Lower and upper bounds of the 90% confidence interval for R.Sz_mean: Machine-learning predicted concentration of soil-respired CO₂ (ppm).Sz_std: 1σ uncertainty of Sz (ppm).Sz_90_low, Sz_90_high: Lower and upper bounds of the 90% confidence interval for Sz.CO2_mean: Reconstructed atmospheric CO₂ concentration (ppm).CO2_std: 1σ uncertainty of the reconstructed atmospheric CO₂ (ppm).CO2_90_low, CO2_90_high: Lower and upper bounds of the 90% confidence interval for the reconstructed CO₂.Gallagher, T. M. et al. Regional Patterns in Miocene-Pliocene Aridity Across the Chinese Loess Plateau Revealed by High Resolution Records of Paleosol Carbonate and Occluded Organic Matter. Paleoceanogr. Paleoclimatology 36, e2021PA004344 (2021).Da, J. Rainy spring delayed the late Neogene expansion of C4 biomass over East Asia. 78003 Bytes figshare https://doi.org/10.6084/M9.FIGSHARE.29137106.V1 (2025).Tipple, B. J., Meyers, S. R. & Pagani, M. Carbon isotope ratio of Cenozoic CO2: A comparative evaluation of available geochemical proxies: CENOZOICδ13CCO2. Paleoceanography 25, (2010).