Seafloor microplastic hotspots controlled by deep-sea circulation

Elucidating the vertical transport of microplastics in the water column: A review of sampling methodologies and distributions

There have been numerous studies that have investigated floating microplastics (MPs) in surface water, yet little data are currently available regarding the vertical distribution in the water column. This lack constrains our ability to comprehensively assess the ecological effects of MPs and develop further policy controls. In this study, we reviewed current progress of sampling methodologies, the distribution patterns, and the physiochemical properties of MPs throughout the water column. Three sampling protocols were identified in this study: bulk, net and submersible pump/in-situ sampling. In different regions, the vertical patterns of MPs in the water column varied with depth, which is possibly related to the morphological characteristics, polymeric densities, and biofouling of the MPs. The results of this review revealed that fibrous and fragmented MPs comprised over 90% of the total MPs by quantity, of which fibrous MPs constituted the majority (43%-100%). In addition, polyethylene terephthalate, polyamide, polyethylene, polyvinyl chloride, and polypropylene have been widely identified in previous studies. To minimize the impact caused by various sampling protocols, the use of a volume gradient trail experiment and a unified mesh size of 60-100 μm for the initial concentration are recommended according to the results of this review. Given the limited knowledge regarding the vertical transport of MPs in the water column, harmonized sampling methods should first be developed. The mechanisms of this process can be separately considered for different water bodies, such as freshwater systems, coastal waters, and pelagic zones. The presence of these anthropogenic pollutants in the water column poses a threat to the largest but most vulnerable habitats of life on earth, and hence they merit further investigation.

Microplastic pollution in a rapidly changing world: Implications for remote and vulnerable marine ecosystems

Ecosystems in remote regions tend to be highly specific, having historically evolved over long timescales in relatively constant environmental conditions, with little human influence. Such regions are amongst those most physically altering and biologically threatened by global climate change. In addition, they are increasingly receiving anthropogenic pollution. Microplastic pollution has now been found in these most remote places on earth, far from most human activities. Microplastics can induce complex and wide-ranging physical and chemical effects but little to date is known of their long-term biological impacts. In combination with climate-induced stress, microplastics may lead to enhanced multi-stress impacts, potentially affecting the health and resilience of species and ecosystems. While species in historically populated areas have had some opportunity to adapt to mounting human influence over centuries and millennia, the relatively rapid intensification of widespread anthropogenic activities in recent decades has provided species in previously 'untouched' regions little such opportunities. The characteristics of remote ecosystems and the species therein suggest that they could be more sensitive to the combined effects of microplastic pollution, global physical change and other stressors than elsewhere. Here we discuss how species and ecosystems within two remote yet contrasting regions, coastal Antarctica and the deep sea, might be especially vulnerable to harm from microplastic pollution in the context of a rapidly changing environment.

The Way of Macroplastic through the Environment

With the focus on microplastic in current research, macroplastic is often not further considered. Thus, this review paper is the first to analyse the entry paths, accumulation zones, and sinks of macroplastic in the aquatic, terrestrial, and atmospheric environment by presenting transport paths and concentrations in the environment as well as related risks. This is done by applying the Source–Pathway–Receptor model on macroplastic in the environment. Based on this model, the life cycle of macroplastic is structurally described, and knowledge gaps are identified. Hence, current research aspects on macroplastic as well as a sound delimitation between macro- and microplastic that can be applied to future research are indicated. The results can be used as basic information for further research and show a qualitative assessment of the impact of macroplastic that ends up in the environment and accumulates there. Furthermore, the applied model allows for the first time a quantitative and structured approach to macroplastic in the environment.

Seafloor microplastic hotspots controlled by deep-sea circulation

Although microplastics are known to pervade the global seafloor, the processes that control their dispersal and concentration in the deep sea remain largely unknown. Here, we show that thermohaline-driven currents, which build extensive seafloor sediment accumulations, can control the distribution of microplastics and create hotspots with the highest concentrations reported for any seafloor setting (190 pieces per 50 grams). Previous studies propose that microplastics are transported to the seafloor by vertical settling from surface accumulations; here, we demonstrate that the spatial distribution and ultimate fate of microplastics are strongly controlled by near-bed thermohaline currents (bottom currents). These currents are known to supply oxygen and nutrients to deep-sea benthos, suggesting that deep-sea biodiversity hotspots are also likely to be microplastic hotspots.