Nemoto, Karin; Yokoyama, Yusuke; Obrochta, Stephen P; Miyairi, Yosuke; Fujiwara, Osamu; Yamamoto, Shinya; Nakamura, Atsunori; Hubert-Ferrari, Aurélia; Heyvaert, Vanessa; De Batist, Marc (2024): Quartz flux at Lake Motosu Site MOT15-2 [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.965002 (DOI registration in progress)

Quantitative X-ray diffraction (XRD) analysis was performed on 109 samples to determine the amount of quartz in MOT15-2 core using a Bruker D2 Phaser at the Atmosphere and Ocean Research Institute, The University of Tokyo. Slit width was 0.4 mm, and with a 4˚ soller slit. Measurements were performed between 20˚ and 35˚ 2θ at a 0.01˚ step for 0.2 seconds per step. The area of the quartz peak (~26.6˚) was determined by trapezoidal numerical integration using MATLAB. Prior to XRD measurement, samples were first pretreated with H₂O₂ to dissolve organic matter, then treated with sodium hexametaphosphate to disaggregate the clay minerals. Next, samples were centrifuged for 5 minutes to settle particles coarser than 2 µm. The supernatant solution was reserved for later clay-mineral analysis, which is not discussed in this study. Samples were dried, crushed, and packed into measurement holders. Six standards were prepared for quantitative conversion of peak area to mineral percentage by mixing known amounts of quartz (Quartz Granular from Wako Pure Chemical Industries, Lot. SDE2986) and calcite (Calcium carbonate, 4N made by Kanto Kagaku, Lot. 208N2154). Calcite is used to dilute quartz because it is not naturally occurring in the lake and its peak does not interfere with quartz peaks. Standards consist of 5, 10, 15, 20, 25 and 30% quartz. These standards were measured under identical conditions as the samples. A linear model was fit to the known percentages and peak areas. Volume of samples freeze-dried in the cube was measured to obtain the quartz deposition flux by a Micromeritics Gas Pycnometer AccuPyc II (1340 series), which uses a substitution of He gas, at Atmosphere and Ocean Research Institute, University of Tokyo. We calculated quartz flux at Lake Motosu by multiplying obtained quartz percentage, dry bulk density and sedimentation rate. Volcanic layers are considered to be instantaneous when calculating sedimentation rate. Sedimentation rate is calculated using age-depth model provided by Obrochta et al. (2018).