Structural and chemical analysis of marine aggregates: In situ macrophotography and laser confocal and electron microscopy

Marine-snow aggregates are compositionally diverse macroparticles that dominate the vertical material flux in many open-ocean environments. There is little documentation of the detailed physical structure and microcomposition of marine-snow aggregates, yet such characteristics both influence and are a function of aggregation mechanisms. This paper describes the application of in situ macrophotography followed by laser-scanning confocal microscopy (LSCM) as a means of observing the fine structure of delicate marine-snow aggregates in their fully hydrated state. Use of specific fluorescent stains yielded microcompositional images, and addition of analytical scanning electron microscopy allowed analysis of subcomponent particles within the aggregates. Application of these techniques to structurally diverse aggregates collected from the oligotrophic North Pacific surface waters revealed large variations in structure, density, relative homogeneity, extracellular matrix material, abundance and type of phytoplankton, and organic and mineral microcomposition.