A novel method to measure calcium carbonate with portable X-ray fluorescence instrumentation and its application to Gulf of Mexico surficial sediments

摘要

A novel, rapid, low cost, non-destructive and reliable technique was developed to simultaneously measure calcium carbonate (CaCO3) and trace element concentrations in sediments with a portable X-ray fluorescence (pXRF) analyzer, and applied to 27 samples of surficial sediments collected from the Yucatan continental shelf (230 m water depth) and 33 samples from deep sediments (1200 m water depth) of the Gulf of Mexico. This technique is based on calculation of authigenic calcium (Ca-auth) from the total Ca measured with the pXRF. Results obtained with the pXRF showed a very high and highly significant correlation (r = 0.99, P 0.001) with measurements of inorganic carbon (C-i) obtained by coulometry, with a slope of 0.972 +/- 0.014 SD and negative Y-intercept of -0.403 +/- 0.093 SD. The latter is consistent with the presence of carbonates unrelated to Ca (e.g., MgCO3, SrCO3, MnCO3, FeCO3) that were not detected by the pXRF. Statistical analysis indicated that the means of C-i and Ca-auth did not differ significantly, thus yielding reliable measurements with the pXRF. The C-i concentrations can be calculated directly from Ca-auth or, alternatively, from several sediment samples measured by coulometry (or other reliable method) whereby C-i can be calculated from the linear regression between these two parameters. Finally, Ca-a(u)th and titanium showed an inverse relationship, suggesting that carbonates act as diluents of terrigenous material, especially in the western side of the Gulf of Mexico where riverine transport of this land-derived material is more intense. (C) 2020 Elsevier B.V. All rights reserved.