A Path Towards Modeling Marine Particle Disaggregation through In-Situ Measurements of Fragmentation Strength

Marine particle dynamics have large implications on biogeochemical transport in coastal and open ocean waters. Particle export is largely linked to sedimentation, where settling rate depends most strongly on particle size. Fluid shear and other physical forces govern the size of suspended particles through aggregation and fragmentation. State-of-the-art biogeochemical models include aggregation in their predictions, but either oversimplify disaggregation or neglect it altogether. This has led to large uncertainties in our predictive capabilities of particle export. Attempts to model disaggregation have proven difficult due to the complexity of naturally occurring marine particulate matter, which can vary both spatially and temporally as changes to the suspended population occur with coastal runoff, blooms of phytoplankton, and other factors. As a path towards developing disaggregation models, we present some of the first in-situ measurements of marine particle disaggregation and fragmentation strength. Marine particles in near-surface coastal and pelagic waters were exposed to calibrated turbulence using custom-built disaggregation equipment. Particle breakup response was quantified through changes in their size distributions measured with a LISST-100X. Aggregate fragmentation strength was estimated through measurements of the largest aggregate size, which decreased with increasing dissipation rate of turbulent kinetic energy. The fragmentation strength of coastal and pelagic particles is presented and the utility of this new information for describing disaggregation dynamics within biogeochemical modeling frameworks is discussed.