The global biological microplastic particle sink

Abstract

Every year, about four percent of the plastic waste generated worldwide ends up in the ocean. What happens to the plastic there is poorly understood, though a growing body of evidence suggests it is rapidly spreading throughout the global ocean. The mechanisms of this spread are straightforward for buoyant larger plastics that can be accurately modelled using Lagrangian particle models. But the fate of the smallest size fractions (the microplastics) are less straightforward, in part because they can aggregate in sinking marine snow and faecal pellets. This biologically-mediated pathway is suspected to be a primary surface microplastic removal mechanism, but exactly how it might work in the real ocean is unknown. We search the parameter space of a new microplastic model embedded in an earth system model to show that biological uptake can significantly shape global microplastic inventory and distributions and even account for the budgetary “missing” fraction of surface microplastic, despite being an inefficient removal mechanism. While a lack of observational data hampers our ability to choose a set of “best” model parameters, our effort represents a first tool for quantitatively assessing hypotheses for microplastic interaction with ocean biology at the global scale.

Sinking microplastics in the water column: simulations in the Mediterranean Sea

“…They provide a total amount of yearly plastic release into the Mediterranean in the range 2200-4000 t, from which around 37 % corresponds to negatively buoyant plastic, and 6 % are due to maritime activity. This 37 % agrees well with previous global estimations (Lebreton et al, 2018).…”

Sinking microplastics in the water column: simulations in the Mediterranean Sea

“…They provide a total amount of yearly plastic release into the Mediterranean in the range 2200 − 4000 tonnes, from which around 37% corresponds to negatively buoyant plastic, and 6% are due to maritime activity. This 37% agrees well with previous global estimations (Lebreton et al, 2018).…”

Zooplankton grazing of microplastic can accelerate global loss of ocean oxygen

“…Biological uptake has the potential to profoundly shape microplastic particle distributions in the global ocean 7 , concentrating particles in biologically-active surface regions as well as in gyres, and transporting particles to the deep ocean. Figure 1 displays simulated microplastic concentrations from a model that does not include biological uptake (No Bio) and from three models that do; ‘Low Concentration’ (LC), ‘High Concentration’ (HC), and ‘Moderate Concentration’ (MC).…”

“…Figure 1 displays simulated microplastic concentrations from a model that does not include biological uptake (No Bio) and from three models that do; ‘Low Concentration’ (LC), ‘High Concentration’ (HC), and ‘Moderate Concentration’ (MC). These three simulations are highlighted to represent the solution space of the 14 individuals of a 300 member perturbed parameter ensemble 7 , 8 that produced plausible global microplastic inventories 9 and subsurface particle maxima 10 , using pollution rates 11 and marine snow aggregation rates 12 within available estimates. Microplastic model parameter values for each simulation presented here are provided in Table 1 .…”

“…If sufficiently widespread, this reduction of grazing on primary producers might have global biogeochemical consequences. Explicit consumption of microplastic by zooplankton, as well as microplastic aggregation in marine snow, was recently implemented in an Earth system model in order to simulate the transport of microplastic particles by biology 7 . They demonstrated a potentially significant influence of both marine snow (aggregated organic detrital material) and zooplankton faecal pellets in shaping microplastic distributions in the global ocean.…”