Measurements of the Size and Physical Properties of Marine Particles Using Atomic Force Microscopy: Implications for Marine Biogeochemical Cycles

Abstract Particle size and physical properties such as stiffness and adhesiveness affect sinking velocity and flux in the ocean, yet conventional two‐dimensional measurements lack accuracy and mechanical information. In this study, we applied atomic force microscopy (AFM) to quantify three‐dimensional size and physical properties of marine particles. Three hundred and sixty‐eight particles were collected using a marine snow catcher from the pycnocline and benthic boundary layer at three coastal‐to‐offshore stations in the northwestern Pacific. Particle equivalent spherical diameters (ESDs) ranged from 0.4 to 32 μm, with >70% smaller than 10 μm. Two‐dimensional analyses overestimated ESDs of settled particles by ∼1.5 times (∼3.3 times in volume) relative to three‐dimensional measurements. Young's modulus (0.07–616 MPa) and adhesiveness (331–2,802 pN) varied widely and overlapped reported values for bacteria, diatoms, and mucus. Particle physical properties differed systematically with depth and location, indicating that AFM provides critical constraints on particle dynamics, origins, and marine biogeochemical cycles.