[A-CG41] Biogeochemical linkages between the surface ocean and atmosphere

[ACG41-P01] Applying the complex amplitude sensor to measure the size-resolved concentrations and compositions of suspended particulate matter in the ocean

*Atsushi Yoshida¹, Yutaka Tobo¹, Kouji Adachi², Nobuhiro Moteki³, Yoshimi Kawai⁴, Kosei Sasaoka⁴, Makoto Koike⁵ (1.National Institute of Polar Research, 2.Meteorological Research Institute, 3.Tokyo Metropolitan University, 4.Japan Agency for Marine-Earth Science and Technology, 5.The University of Tokyo)

Keywords:Oceanic suspended particulate matter, Marine aerosols, Biogeochemical cycle

Oceanic suspended particulate matter (SPM) plays important roles in the coupling of climate and biogeochemical cycles via ocean-atmosphere interactions. However, methods for quantifying the properties of SPM in seawater have not yet been well established. Here we present the application of the recently developed complex amplitude sensor (CAS) for analyzing the complex forward-scattering amplitude of individual SPM (0.2–5.0 µm in diameter) obtained at depths of 0–100 m during a research cruise in the northwest Pacific. The measured distribution of the complex amplitude indicated that the CAS-derived SPM data can be roughly classified into five major types. The comparison with the complex amplitude data on reference samples combined with scanning electron microscopy suggests that these types would be mainly attributed to diatom fragments, carbonaceous materials (likely, organic matter), mineral dusts, iron oxides, or black carbon. The depth profiles reveal that higher concentrations of SPM, presumably dominated by diatom fragments and carbonaceous materials with peak diameters of 0.7–1.0 µm, were typically observed along with the layers of elevated chlorophyll a concentrations and turbidity values. Based on this case study, we discuss potentials and challenges of the CAS instrument in measuring the size-resolved concentrations and compositions of SPM in seawater.