Research on climate change based on carbonate porosity analysis in Jinping, China

climate change (porosity change) curve obtained using saddle line 2 in Table 1 (Column F). Fig 7f shows the climate change (porosity change) curve obtained using saddle line 3 in Table 1 (Column H). Fig 7h shows the climate change (porosity change) curve obtained using saddle line 4 in Table 1 (Column J). 3.4 Using the existing data from published papers to obtain the climate change curve for the Jinping area A great deal of climate research [27–78] has been conducted in western Sichuan, China, where the Jinping area is located. These studies provide a good comparative basis for climate change research in the Jinping area. However, some of the data in these papers are conflicting. To compare the existing data with the curve established from the porosity in this study, the results of the published papers on climate change in western Sichuan and adjacent areas were orga- nized into a curve. This curve needs to reflect the trend of the climate change, not necessarily the value of the temperature at a certain point in time. Therefore, in this study, only the climate change curve was needed, not the temperature change curve. The climate change curve used in this study was the climate change trend curve. To facilitate the creation of the curves from the published data, the following principles of curve data collation were employed. Because the number of stalagmite studies in western Sichuan and the adjacent areas is relatively small, when the data were contradictory, the data were used in the order of loess, tree ring, sediment,

and geomagnetism data. Data derived from historical documents were used when only histori- cal document data and sediment data were available. In the event of conflicting data for the same region, the most recently published data were used. When data from different regions conflicted, the data from the region closer to western Sichuan were used. When of the results of loess or geomagnetic studies conducted in the same area conflicted, the most recently pub- lished results were used. When the climate change curves were constructed, the upper limit of the curve was set to 40 and the lower limit was set to 10. The baseline value for the climate change curve was set to 20. These values do not refer to temperature. The data points selected from the published articles were converted to stratigraphic ages first. The curve values for the research conducted using loess and sediments were adjusted according to the upper limit of 40 and the lower limit of 10. For the papers without climate change curves, the climate change values were determined based on the hot and cold descriptions in the paper. If the temperature was hot, the value was set as 35; if the temperature was warm, the value was set as 25; if the temperature was low, the value was set as 20; and if the temperature was cold, the value was set as 15. Even if the upper and lower temperature limits of the curve were reset, this would not affect the overall trend of the climate change curve. Therefore, in this study, the data from the published papers were used to organize the climate change curve and compare it with the

porosity change curve. Fig 8a shows the climate change trend map compiled using data from published papers; and Fig 8b shows the climate change (porosity change) curve obtained using saddle line 1 in Table 1 (Column D). It can be seen that the other curves are quite different from the climate change curve compiled using data from published studies. 4 Discussion and analysis In climate change research conducted using carbonate stalagmites, the gray values of stalag- mite profile images are often used to construct climate change curves. However, when using polarized light microscope images of carbonate rocks to conduct local climate change research, the use of grayscale images lacks the corresponding geological indicators. When using stalag- mite profile images to conduct local climate change research, the use of gray values to PLOS ONE Research on climate change based on carbonate porosity analysis in Jinping PLOS ONE | https://doi.org/10.1371/journal.pone.0281630 March 30, 2023 14 / 21