## 1 Introduction
Earlier works on modeling of microplastic transport in the high latitudes of the northern hemisphere did not include parameterizations of biofilm accumulation on the particles [35; 36; 37; 38]. An attempt to incorporate basic parameterizations of biofouling in the North Atlantic (Baltic Sea) region was made by [PERSON] et al., 2022 [39] and [PERSON] et al., 2023 [40]. These studies employed disparate methodologies for characterizing biomass growth on the particle and microplastic release into bottom sediments. However, both studies assumed the impossibility of biofilm degradation, which resulted in particle clearing and buoyancy restoration. The work presented by the [PERSON] et al., 2021 [41] introduced a unique module in conjunction with a biogeochemical model that describes the transition of microplastic concentrations between four distinct states: free-floating, with a biofilm, absorbed by zooplankton, and in detritus particles. The MP module was applied to a 2D coupled benthic-pelagic vertical transport model in the Oslo Fjord. The approach was limited by the assumptions that each microplastic category had a different constant vertical velocity, and the effects of stratification on the particle distribution were not taken into account. However, the Berezina model allowed for the modeling of the main features of microplastic transformation with respect to the interaction with biota. A more advanced model for the biofouling of microplastic particles was proposed by [PERSON] et al., 2017 [42]. The model included parameterization of the processes of biofilm accumulation (collision of the particles with algae, algae growth limited by light and temperature) and degradation (respiration, mortality). The authors evaluated the impact of biofouling on the vertical distribution of microplastics in various fixed water columns, representative of the typical patterns observed in different regions of the global ocean. The northern point was located in the North Atlantic near Iceland. The one-dimensional tests demonstrated that the vertical movement of microplastic particles, depending on their size, resulted in the maximum concentration occurring at intermediate depths. Subsequently, [PERSON] et al., 2021 [43] applied the Kooi model to estimate the global transport of microplastics while integrating 3D advection. The next advancement of the Kooi model was presented by [PERSON] et al., 2022 [44], who incorporated a dynamic calculation of grazing instead of a constant rate of algae mortality and considered additional biofilm losses such as those from viruses. Nevertheless, the implementation of the enhanced biofouling model was conducted in three regions, with their environmental conditions being markedly disparate from those observed in polar latitudes. Consequently, the practical applicability of these innovations to the Arctic Ocean remains uncertain, largely due to the dearth of empirical data pertaining to the parameterization of these processes. In our previous research [45], a three-dimensional modeling approach was employed to investigate the potential trajectories of microplastics released from the Siberian Rivers into the Kara Sea. The aim of that study was to clarify the most critical physical processes influencing the transport and distribution of microplastics in the Arctic. It was demonstrated that the effects of microplastic embedding in sea ice and particle biofouling play a key role in influencing the trajectories of floating particles and their deposition on the seafloor. A shortcoming of that study was the use of an overly simple biofouling model that did not account for several important processes that affect biofilm dynamics. To simulate biofilm dynamics in the present study, we used a biofouling model that was built according to [PERSON] et al., 2017 [42]. The objective of our study was to simulate the behavior of microplastic particles of different sizes in polar waters.