Polycarbonate

Triplicate samples of 200–300 mL were filtered through 20 (nylon, Millipore), 2 (polycarbonate, Whatman) and 0.2 (polycarbonate, Whatman) μm aperture sized membranes in time series, and total Chl a concentrations were calculated by combining size-separated Chl a concentrations for the 20 L incubation systems, and 100–150 mL were filtered through a GF/F membrane (Whatman) to measure total Chl a for the 2 L incubation systems. The pigments on the membranes were extracted with 90% acetone at -20 °C for 20 h in the dark. The extract was used for measuring Chl a using a 7200-000 Trilogy fluorometer (Turner Designs)^{47 (link)}.

For acidic dissolution, goethite particles (0.4 g L⁻¹) were exposed to ultrapure water at pH 2 and 5 (adjusted using 1 m HCl and 1 m NaOH) for 24 h. For basic dissolution, similar experiments at pH 8 and 11 were conducted, but the reaction proceeded under argon flow to prevent acidification from atmospheric CO₂ dissolution. At the end of each experiment, the solids were separated from the solution by vacuum filtration (Whatman, polycarbonate, 0.2 µm), and dried in a desiccator for 24 h. Particles were then characterized using FIB‐SEM and conventional TEM.
For reductive dissolution, goethite particles (0.4 g L⁻¹) were exposed to 1, 0.1, and 0.01 m hydroxylamine (NH₂OH) in ultrapure water for 24 h. The pH was adjusted to 5 using 1 m HCl and 1 m NaOH. The solids were extracted from the solution by vacuum filtration (Whatman, polycarbonate, 0.2 µm), and placed in the desiccator for further 24 h prior to TEM characterization.