the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
On the magnitude and uncertainties of global and regional soil organic carbon: A comparative analysis using multiple estimates
Abstract. Globally, soil is one of the largest terrestrial carbon reservoirs, with soil organic carbon (SOC) regulating overall soil carbon dynamics. Robust quantification of SOC stocks in existing global observation-based estimates avails accurate predictions in carbon climate feedbacks and future climate trends. In this study, we investigated global and regional SOC estimates, based on five widely used global gridded SOC datasets (HWSD, WISE30sec, GSDE, SoilGrids250m, and GSOCmap), a regional permafrost dataset from Mishra et al. (UM2021), and a global-scale soil profile database (the World Soil Information Service soil profile database, WoSIS) reporting measurements of a series physical and chemical edaphic attributes. Our comparative analyses show that the magnitude and distribution of SOC varies widely among datasets, with certain datasets showing region-specific robustness. At the global scale, the magnitude of SOC stocks simulated by GSDE, GSOCmap, and WISE30sec are comparable, while estimates of SoilGrids250m and HWSD are at the upper and lower ends, respectively. Global SOC stocks ranged from 577–1171 Pg C and 1086–2678 Pg C at 0–30 cm and 0–100 cm depth. The spatial distribution of SOC stocks varies greatly among datasets, especially in the northern circumpolar and Tibetan Plateau permafrost regions. In general, the UM2021 and WISE30sec perform better in the northern circumpolar permafrost regions, and GSDE performs better in China. SOC stocks estimated by different datasets also show large variabilities across different soil layers and biomes. Overall, GSOCmap performs well at 0–30 cm depth, while SoilGrids250m and GSDE perform better at multiple depths. Among the five gridded global datasets, SoilGrids250m exhibits a more consistent spatial pattern and depth distribution with WoSIS. Large uncertainties in existing global gridded SOC estimates are generally derived from soil sampling density, diverse sources and mapping methods for soil datasets. We call for future efforts for standardizing soil sampling efforts, cross-dataset comparison, proper validation, and overall global collaboration to improve SOC estimates. The data are available at https://doi.org/10.6084/m9.figshare.20220234 (Lin et al., 2022).
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- RC1: 'Comment on essd-2022-232', Anonymous Referee #1, 02 Dec 2022
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RC2: 'Comment on essd-2022-232', Anonymous Referee #2, 22 Dec 2022
essd-2022-232
On the magnitude and uncertainties of global and regional soil organic carbon: A comparative analysis using multiple estimates
The authors used five datasets to compare the global soil carbon pool density and its regional distribution characteristics. The authors conclude that among the five gridded global datasets, SoilGrids250m exhibits a more consistent spatial pattern and depth distribution with WoSIS. The overall quality of the manuscript is good in line with the theme of the journal. However, I think the author should have made some improvements before publication, which I think would have helped to improve the quality of the manuscript. The authors used 5 databases, however, I found that some information was missing. For example, the issue of the number of samples per database and the distribution of these samples. For example, the SoilGrids250m database has a high spatial resolution compared to the other databases, which means that this database has more sample points and therefore this result is more accurate. Therefore, it is not surprising that the current conclusions are based on such results. In addition, the global sample distribution area of each database also determines the data variability and characteristics of its different regional organic carbon pools. I suggest the authors to provide the size of the number of samples and map their regional distribution so that the data characteristics can be clarified. In addition, the discussion section needs to be strengthened to avoid re-description of the results whenever possible.
Due to the lack of line numbers, I can only circle them by this “”
“Globally, soil is one of the largest terrestrial carbon reservoirs, with soil organic carbon (SOC) regulating overall soil carbon dynamics”. In my opinion, “soil organic carbon (SOC) regulating overall soil carbon dynamics” formulation is wrong, please modify. You can say that its small changes have a significant impact on global carbon cycle.
“Soil stores twice the amount of carbon in atmosphere and vegetation combined thus plays a fundamental role in the global carbon cycle (Piao et al., 2009; Bastida et al., 2019)” Now there are also studies that point out that soils are 3-4 times the sum of atmospheric and vegetation carbon pools, so is it appropriate to use a defined multiplier of 2? Please check out the following papers:
Lehmann, J., Kleber, M., 2015. The contentious nature of soil organic matter. Nature. doi:10.1038/nature16069
Line 120 “where ððð¶ð· is SOC density (t ha-1), ððð¶ð¶ is SOC content (% weight), ðµð· is soil bulk density (g cm-3), ð· is the depth of soil layers (cm), and ð¶ð¹ is the coarse fragments (% weight)” What is the meaning of coarse fragments here? Not clear, this coarse component particle size is a fixed value, please revise.
Figure 4 and 7. Change font colour for labels of correlation coefficient and normalized standard deviation to match the lines. Perhaps add the various contour lines to legend for clarity. How to get normalized standard deviation in Taylor diagram Fig 4. The Taylor diagram in Fig 4 should be explained. Provide some guidance on interpretation of Taylor diagram in text as they aren't that commonly used in in soils studies.
Line 230-235 “Relatively, the SOC density simulated by GSDE, SoilGrids250m and UM2021 are
closer to the pattern of SOC distribution based on the Tibetan Plateau observations, with high values in the forest of southeastern Tibetan Plateau and low values in the desert of northwestern Tibetan Plateau (Wang et al., 2019; Tian et al., 2008)” Why is there a reference in the results section?
Line 265-275 The discussion section should be more explanatory of the results rather than more repetitive of the results, and the authors need to revise these issues.
Citation: https://doi.org/10.5194/essd-2022-232-RC2
Status: closed
- RC1: 'Comment on essd-2022-232', Anonymous Referee #1, 02 Dec 2022
-
RC2: 'Comment on essd-2022-232', Anonymous Referee #2, 22 Dec 2022
essd-2022-232
On the magnitude and uncertainties of global and regional soil organic carbon: A comparative analysis using multiple estimates
The authors used five datasets to compare the global soil carbon pool density and its regional distribution characteristics. The authors conclude that among the five gridded global datasets, SoilGrids250m exhibits a more consistent spatial pattern and depth distribution with WoSIS. The overall quality of the manuscript is good in line with the theme of the journal. However, I think the author should have made some improvements before publication, which I think would have helped to improve the quality of the manuscript. The authors used 5 databases, however, I found that some information was missing. For example, the issue of the number of samples per database and the distribution of these samples. For example, the SoilGrids250m database has a high spatial resolution compared to the other databases, which means that this database has more sample points and therefore this result is more accurate. Therefore, it is not surprising that the current conclusions are based on such results. In addition, the global sample distribution area of each database also determines the data variability and characteristics of its different regional organic carbon pools. I suggest the authors to provide the size of the number of samples and map their regional distribution so that the data characteristics can be clarified. In addition, the discussion section needs to be strengthened to avoid re-description of the results whenever possible.
Due to the lack of line numbers, I can only circle them by this “”
“Globally, soil is one of the largest terrestrial carbon reservoirs, with soil organic carbon (SOC) regulating overall soil carbon dynamics”. In my opinion, “soil organic carbon (SOC) regulating overall soil carbon dynamics” formulation is wrong, please modify. You can say that its small changes have a significant impact on global carbon cycle.
“Soil stores twice the amount of carbon in atmosphere and vegetation combined thus plays a fundamental role in the global carbon cycle (Piao et al., 2009; Bastida et al., 2019)” Now there are also studies that point out that soils are 3-4 times the sum of atmospheric and vegetation carbon pools, so is it appropriate to use a defined multiplier of 2? Please check out the following papers:
Lehmann, J., Kleber, M., 2015. The contentious nature of soil organic matter. Nature. doi:10.1038/nature16069
Line 120 “where ððð¶ð· is SOC density (t ha-1), ððð¶ð¶ is SOC content (% weight), ðµð· is soil bulk density (g cm-3), ð· is the depth of soil layers (cm), and ð¶ð¹ is the coarse fragments (% weight)” What is the meaning of coarse fragments here? Not clear, this coarse component particle size is a fixed value, please revise.
Figure 4 and 7. Change font colour for labels of correlation coefficient and normalized standard deviation to match the lines. Perhaps add the various contour lines to legend for clarity. How to get normalized standard deviation in Taylor diagram Fig 4. The Taylor diagram in Fig 4 should be explained. Provide some guidance on interpretation of Taylor diagram in text as they aren't that commonly used in in soils studies.
Line 230-235 “Relatively, the SOC density simulated by GSDE, SoilGrids250m and UM2021 are
closer to the pattern of SOC distribution based on the Tibetan Plateau observations, with high values in the forest of southeastern Tibetan Plateau and low values in the desert of northwestern Tibetan Plateau (Wang et al., 2019; Tian et al., 2008)” Why is there a reference in the results section?
Line 265-275 The discussion section should be more explanatory of the results rather than more repetitive of the results, and the authors need to revise these issues.
Citation: https://doi.org/10.5194/essd-2022-232-RC2
Data sets
Global SOC datasets for 0-30 cm and 0-100 cm depths Ziqi Lin, Yongjiu Dai, Umakant Mishra, Guocheng Wang, Wei Shangguan, Wen Zhang, Zhangcai Qin https://doi.org/10.6084/m9.figshare.20220234
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