Estimation of Mg/Ca Ratios in Biogenic Mg‐Calcites in Methane‐Derived Authigenic Carbonate From the Ulleung Basin, Korea, Using Raman Spectroscopy

ABSTRACT Raman spectroscopy is a powerful optical tool that provides nondestructive analysis with minimal sample preparation and structural information, making it widely used in planetary and deep‐sea research. Although Raman spectroscopy has shown potential for estimating Mg/Ca ratios in Mg‐calcites, data for biogenic Mg‐calcites from diverse marine regions remain limited. Here, we investigated the relationship between Raman spectral parameters (peak position and width) and chemical composition (Mg/Ca molar ratios) in 50 biogenic Mg‐calcites in methane‐derived authigenic carbonate (MDAC) from Site 16GH‐P3 in the Ulleung Basin, Korea. Using electron probe microanalysis, we obtained Mg# (=Mg/[Mg + Ca], mol%) values ranging from 0 to 13.8 mol% in biogenic Mg‐calcites (foraminifera, coccolithophore, and unidentified species). By combining chemical composition data with Raman spectral results, we derived positive correlation equations for CO 3 2− vibrational modes, consistent with previous studies. These equations demonstrate a strong correlation between Raman spectral features and Mg/Ca ratios, highlighting the usefulness of Raman spectroscopy in estimating Mg/Ca ratios in biogenic Mg‐calcites. Through analysis of foraminifera from MDAC with Mg# of 0.1 mol%, we propose to use both peak widths and positions in estimating Mg/Ca ratios in biogenic Mg‐calcites. Our study expands the data set for using Raman spectral features to estimate Mg/Ca ratios in biogenic Mg‐calcites, providing a valuable reference for future Raman applications.