Modeling the influence of biogeochemical processes on the transport of microplastics in the Arctic Ocean

Microplastics (MPs) are plastic fragments less than 5 mm in size. At present, all natural environments, including the World Ocean, are polluted with MPs from the poles to the equator.The study tests the hypothesis that seasonality of processes in the marine ecosystem can affect the vertical transport of MPs in the water column (through changes in density due to biofouling and absorption and excretion of MP particles by zooplankton). The work used the biogeochemical model OxyDep (Yakushev et al., 2011) to reproduce the seasonality of marine ecosystem. BioPlast (Berezina et. al. 2021) considers processes of MPs degradation, biofouling, ingestion of particles by zooplankton and MPs in detritus. OxyDep biogeochemical module and MP module BioPlast were coupled with ROMS-20 (20 km resolution) 3D transport model using the FABM framework (Bruggeman & Bolding, 2014). The applied models describe the transformation of MPs and reproduce in detail the effect of ecosystem and biogeochemical processes on its vertical and horizontal transport, as well as on its burying in sediments.MPs were supplied to the Arctic Ocean from rivers flowing into the White, Barents, Kara and East Siberian Seas, as well as from the Atlantic Ocean, excluding any other sources. It was shown that within 8 years MPs spreads throughout the Arctic Ocean, except for the Canadian Basin. Several numerical experiments were conducted, MPs of Atlantic origin dominate in the western part of the Arctic Ocean. According to the upper estimate, the MPs from the North Atlantic occupies almost the entire water area of the Arctic Ocean. At the same time, the concentrations of MP covered with biofilm, MP in zooplankton, and MP in detritus are quite low compared to the virgin form of MP. A short-term purification of the surface layer from MP due to biofouling and sedimentation with detritus was observed in the estuarine zones and in the Fram Strait. This is partly due to the low productivity of the Arctic Ocean and the short period of phytoplankton blooms, and partly to the limitations of the BioPlast model. Further work will be devoted to the analysis of other sources of microplastics in the Arctic Ocean, such as the supply of MPs through the Bering Strait and local sources associated with maritime activity on the Northern Sea Route.The development of the described model is of great importance, especially for the Arctic region, where regular observations of MPs are not available, and the ecosystem is extremely vulnerable to anthropogenic impact.