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

4.2 Problems that should be paid attention to in establishing climate change curves using rock porosity The following issues should be paid attention to when using polarized images of carbonate rocks to create porosity curves for use in climate change research. 1) The porosity obtained from a single polarized image of a carbonate rock via image analysis cannot be regarded as the value for the rock sample. Because the single polarized image only captures part of the rock slide. 2) The average rock porosity of multiple polarized images of a carbonate rock slide can- not be regarded as the value for the rock sample. At least these images should be divided into two groups, and the average rock porosity of each group should be calculated separately, and then, the two average values of the rock porosity of the two groups should be compared. If the average values of the rock porosities of the two groups are close, the current porosity identifi- cation algorithm is reliable. 3) The average rock porosity obtained via analysis of polarized images of carbonate rocks should be verified by measuring the porosity of the rock sample using the standard method. 4) If the average porosity obtained via analysis of polarized images of a carbonate rock is quite different from the measured porosity of the sample, the image anal- ysis algorithm should be adjusted using the measured porosity of the sample as the target value. The average porosity obtained using the image analysis method should gradually approach the measured porosity of the sample.

4.3 Can this research method be used in other regions? In other regions where regional climate change research needs to be conducted, the research method discussed in this study can be used as a reference. When applying the research method to regional climate change research in other regions, attention should be paid to the following premises. 1) There is no local climate research basis such as stalagmites and loess. 2) The research funds are not sufficient to conduct climate change research using stalagmites. 3) The local stratigraphic sequence is clear and detailed geological data are available. 4) The cost of obtaining polarized microscope images of local samples of carbonate rocks is not very high. 5) There is a wide distribution of carbonate rocks locally. As long as the above premises are met, it is feasible to apply the research method described in this paper to other regions. 5 Conclusions In this study, through the analysis of carbonate rock images, the porosity change curve for the Jinping area was obtained. The climate change curve was obtained by collecting the research results of published papers on the Jinping area and its adjacent areas. Through comparison, it was found that the curve established using the saddle line algorithm for the carbonate image was the closest to the curve established using data from the published papers. In this study, the cardioids curvy function was used to fit the curve established using the saddle line algorithm for the carbonate images. The main conclusions of this study are as follows:

1. Published climate change data for Jinping and adjacent areas should be carefully identified when used. The differences in climate change curves obtained using different research methods in the same research area should be carefully analyzed. 2. Climate change will affect the karst development rate of carbonate rocks. Therefore, climate change can be analyzed by studying the porosity change of carbonate rocks. The change in the porosity of carbonate rocks can be used to study climate change in a carbonate rock area. The porosity change of carbonate rocks can be obtained via image analysis. The research on carbonate porosity changes based on image analysis can be used for climate change research in Jinping and adjacent areas. 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 16 / 21