Ocean emission of microplastic

Daniel B Shaw; Qi Li; Janine K Nunes; Luc Deike

doi:10.1093/pnasnexus/pgad296

Ocean emission of microplastic

PNAS Nexus. 2023 Oct 3;2(10):pgad296. doi: 10.1093/pnasnexus/pgad296. eCollection 2023 Oct.

Authors

Daniel B Shaw¹, Qi Li², Janine K Nunes^{1

3}, Luc Deike^{1

4}

Affiliations

¹ Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA.
² School of Civil and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA.
³ Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA.
⁴ High Meadows Environmental Institute, Princeton University, Princeton, NJ 08544, USA.

Abstract

Microplastics are globally ubiquitous in marine environments, and their concentration is expected to continue rising at significant rates as a result of human activity. They present a major ecological problem with well-documented environmental harm. Sea spray from bubble bursting can transport salt and biological material from the ocean into the atmosphere, and there is a need to quantify the amount of microplastic that can be emitted from the ocean by this mechanism. We present a mechanistic study of bursting bubbles transporting microplastics. We demonstrate and quantify that jet drops are efficient at emitting microplastics up to $280 μ m$ in diameter and are thus expected to dominate the emitted mass of microplastic. The results are integrated to provide a global microplastic emission model which depends on bubble scavenging and bursting physics; local wind and sea state; and oceanic microplastic concentration. We test multiple possible microplastic concentration maps to find annual emissions ranging from 0.02 to 7.4-with a best guess of 0.1-mega metric tons per year and demonstrate that while we significantly reduce the uncertainty associated with the bursting physics, the limited knowledge and measurements on the mass concentration and size distribution of microplastic at the ocean surface leaves large uncertainties on the amount of microplastic ejected.

Keywords: air-sea interactions; bubble bursting; microplastics transport; ocean emissions.