X-ray fluorescence spectroscopy (XRF) calibration and its application as a tool to study the Oxygen Minimum Zone variability during the Holocene.

X-ray fluorescence spectroscopy (XRF) is a non destructive analytical technique widely used to estimate the elemental composition of sedimentary records. This analytical technique measure a number of elements in a sample with a resolution similar or better than conventional destructive methods, is quick and requires minimal analytical effort.We tested the precision and reliability of a handheld XRF instrument (DELTA Premium-XRF analyzer) and developed a methodological calibration of the equipment considered to be a potential tool for paleo-environmental investigations, i.e., in the reconstruction of past oxygen concentrations by analyzing redox sensitive trace metals like Mo, which is sequestered from the water column and transferred to the underlying sediments under anoxic and sulfidic conditions (euxinic).Calibration of the instrument was performed using eight certified standards and twelve in-house standards to create a calibration curve and its linear regression model (Pearson, r2=0.98 and p<0.001). Once the XRF was calibrated, the total concentrations of Mo were determined in gravity and multiple cores (NH01-20, 21, 22 and NH01-25, 26, 27) recovered during the CALMEX NH-01 cruise in the eastern slopes of Carmen and Pescadero basins (Gulf of California, Mexico). These sites are intersected by an Oxygen Minimum Zone promoting excellent sediment preservation. All cores were sampled every 1 cm to obtain high-resolution records of the last ~10,000 years. We conclude that handheld XRF enables precise and exact determinations of Mo concentrations in sediments, applied to the characterization of past euxinic environments.