title: The effect of particle properties on the depth profile of buoyant plastics in the ocean.
abstract: Most studies on buoyant microplastics in the marine environment rely on sea surface sampling. Consequently, microplastic amounts can be underestimated, as turbulence leads to vertical mixing. Models that correct for vertical mixing are based on limited data. In this study we report measurements of the depth profile of buoyant microplastics in the North Atlantic subtropical gyre, from 0 to 5 m depth. Microplastics were separated into size classes (0.5-1.5 and 1.5-5.0 mm) and types ('fragments' and 'lines'), and associated with a sea state. Microplastic concentrations decreased exponentially with depth, with both sea state and particle properties affecting the steepness of the decrease. Concentrations approached zero within 5 m depth, indicating that most buoyant microplastics are present on or near the surface. Plastic rise velocities were also measured, and were found to differ significantly for different sizes and shapes. Our results suggest that (1) surface samplers such as manta trawls underestimate total buoyant microplastic amounts by a factor of 1.04-30.0 and (2) estimations of depth-integrated buoyant plastic concentrations should be done across different particle sizes and types. Our findings can assist with improving buoyant ocean plastic vertical mixing models, mass balance exercises, impact assessments and mitigation strategies.
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.|Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University &Research, P.O. Box 47, 6700 AA Wageningen, The Netherlands.
authors.forename: Merel
authors.initials: M
authors.lastname: Kooi
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.
authors.forename: Julia
authors.initials: J
authors.lastname: Reisser
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.
authors.forename: Boyan
authors.initials: B
authors.lastname: Slat
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.
authors.forename: Francesco F
authors.initials: FF
authors.lastname: Ferrari
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.|Takuvik Joint International Laboratory, Département de biologie et Québec-Océan, Université Laval, Quebec G1V 0A6, Canada.
authors.forename: Moritz S
authors.initials: MS
authors.lastname: Schmid
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.
authors.forename: Serena
authors.initials: S
authors.lastname: Cunsolo
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.|Civil Engineering Department, Aalborg University, Fredrik Bajers Vei 5, 9100 Aalborg, Denmark.
authors.forename: Roberto
authors.initials: R
authors.lastname: Brambini
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.|Roger Williams University, Bristol, USA.
authors.forename: Kimberly
authors.initials: K
authors.lastname: Noble
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.
authors.forename: Lys-Anne
authors.initials: LA
authors.lastname: Sirks
authors.affiliation: CABI Europe-Switzerland, Rue des Grillons 1, 2800 Delémont, Switzerland.
authors.forename: Theo E W
authors.initials: TE
authors.lastname: Linders
authors.affiliation: The Ocean Cleanup Foundation, Martinus Nijhofflaan 2, 2624 ES Delft, The Netherlands.|Carl von Ossietzky, University Oldenburg, ICBM-Terramare, Schleusenstr. 1, 26382 Wilhelmshaven, Germany.
authors.forename: Rosanna I
authors.initials: RI
authors.lastname: Schoeneich-Argent
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University &Research, P.O. Box 47, 6700 AA Wageningen, The Netherlands.|IMARES - Institute for Marine Resources &Ecosystem Studies, Wageningen UR, P.O. Box 68, 1970 AB IJmuiden, The Netherlands.
authors.forename: Albert A
authors.initials: AA
authors.lastname: Koelmans