Numerical (No m-3) concentrations (mg m-3) of subsurface microplastic debris collected by bongo net aboard the Scripps Environmental Accumulation of Plastic Expedition (SEAPLEX) cruise, August 2009.

Microplastic was collected using a standard bongo net tow. Each sample was sorted at 6-12x magnification under a Wild M-5 dissecting microscope, and plastic particles and removed for further analysis. Plastic particles were soaked in deionized water to remove salts, dried at 60°C, and stored in a desiccator. Dry mass was measured on an analytical balance. Particles were then digitally imaged with a Zooscan digital scanner (Gorsky et al. 2010). The total number of particles was measured using NIH ImageJ-based tools in the Zooprocess software, calibrated against manual measurements (Gilfillan et al. 2009, Gorsky et al. 2010)