Widespread distribution of microplastics in subsurface seawater in the NE Pacific Ocean

•Microplastic abundance and distribution were characterized in NE Pacific seawater samples.•Microplastic particles (62-5000 μm) were found in seawater at all stations.•Microplastic concentrations were highest nearshore, consistent with land-based sources.•Low microplastic levels SW of Vancouver Island are consistent with La Perouse Bank upwelling.•This assessment provides a basis to evaluate the in-coming debris from Tohoku Tsunami.

We document the abundance, composition and distribution of microplastics in sub-surface seawaters of the northeastern Pacific Ocean and coastal British Columbia. Samples were acid-digested and plastics were characterized using light microscopy by type (fibres or fragments) and size (<100, 100-500, 500-100 and >1000 μm). Microplastics concentrations ranged from 8 to 9200 particles/m3; lowest concentrations were in offshore Pacific waters, and increased 6, 12 and 27-fold in west coast Vancouver Island, Strait of Georgia, and Queen Charlotte Sound, respectively. Fibres accounted for ∼75% of particles on average, although nearshore samples had more fibre content than offshore (p < 0.05). While elevated microplastic concentrations near urban areas are consistent with land-based sources, the high levels in Queen Charlotte Sound appeared to be the result of oceanographic conditions that trap and concentrate debris. This assessment of microplastics in the NE Pacific is of interest in light of the on-coming debris from the 2011 Tohoku Tsunami.

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