Although atmospheric transport and deposition could be an important pathway of terrestrial pollutants to the ocean, little information concerning the presence and distribution of these suspended atmospheric microplastics in marine air is available. We investigated, for the first time, the occurrence and distribution of suspended atmospheric microplastics (SAMPs) in the west Pacific Ocean. In this study, the spatial distribution, morphological appearance, and chemical composition of suspended atmospheric microplastics were studied through continuous sampling during a cruise. SAMPs abundance ranged from 0 to 1.37 n/m3, the median of 0.01 n/m3. Fiber, fragment, and granule SAMPs quantitively constituted 60%, 31%, and 8% of all MPs, respectively. Interestingly, plastic microbeads with numerical proportion of 5% were also observed. A high suspended atmospheric microplastics abundance was found in the coastal area (0.13 ± 0.24 n/m3), while there was less amount detected in the pelagic area (0.01 ± 0.01 n/m3). The amount of suspended atmospheric microplastics collected during the daytime (0.45 ± 0.46 n/m3) was twice the amount collected at night (0.22 ± 0.19 n/m3), on average. Our observations provide field-based evidence that suspended atmospheric microplastics are an important source of microplastics pollution in the ocean, especially the pollution caused by textile microfibers.

Conventional wisdoms on river plume dynamics suggest that a down‐shelf buoyant coastal current will ultimately be trapped at a specific depth, that is, the trapping depth, as constrained by riverine outflow and offshore bottom Ekman transport. Theoretically, a prerequisite down‐shelf current is necessary to form a stable bottom‐trapped river plume. In this study an alternative is described by carrying out a modeling study on the Zhe‐Min Coastal Current (ZMCC). Buoyant water from the Changjiang River is a major factor driving the ZMCC, as is common in bottom‐trapped river plumes; however, the trapping depth is more determined by tidal mixing. When the plume water comes to the sloping topography, strong tidal mixing induces a mixing front, shoreward of which the bottom Ekman layer occupies the entire water column. Such a tidal‐induced front maintains a down‐shelf frontal current, which is intensified both at the surface due to the thermal wind balance and on the top of bottom boundary layer due to the tidal rectification. Direct wind‐induced transport only covers a small fraction of the ZMCC; however, it redistributes the plume water and, thus, affects the coastal current. The tide‐induced frontal trapping depth varies much less between seasons than that predicted by previous plume theories. Instead, it fluctuates strongly in the spring‐neap cycle. Even in summer when upwelling‐favorable winds prevail, the mixing front still sustains a down‐shelf coastal current. Intense tidal mixing exists in many coastal waters, which might be an alternative mechanism in forming bottom‐trapped river plumes and their associated buoyant coastal current.

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A new technique involving large-volume (10 m 3 ) samples of seawater was used to determine the abundance of microplastics (MPs) in the water column in the West Pacific Ocean and the East Indian Ocean. Compared to the conventional sampling methods based on smaller volumes of water, the new data yielded abundance values for the deep-water column that were at least 1−2 orders of magnitude lower. The data suggested that limited bulk volumes currently used for surface sampling are insufficient to obtain accurate estimates of MP abundance in deep water. Size distribution data indicated that the lateral movement of MPs into the water column contributed to their movement from the surface to the bottom. This study provides a reliable dataset for the water column to enable a better understanding of the transport and fate of plastic contamination in the deep-ocean ecosystem.