[M-IS20] Ocean Plastics, an earth science perspective

[MIS20-07] Large-scale distribution and composition of floating plastic debris in the transition region of the North Pacific

*Kentaro Miyazono¹, Rei Yamashita², Hiroomi Miyamoto³, Kazuaki Tadokoro⁴, Yugo Shimizu⁵, Kazutaka Takahashi¹ (1.Graduate school of agricultural and life science, The University of Tokyo , 2.Atmosphere and Ocean Research Institute, The University of Tokyo , 3.Fisheries Research Agency, Hachinohe, 4.Fisheries Research Agency, Shiogama, 5.Fisheries Agency)

Keywords:Microplastics, the North Pacific Ocean, Kuroshio/Kuroshio Extension

Distribution and composition of the floating plastic debris in the transition region across 4600 km between 141ºE to 165ºW in the North Pacific was investigated to obtain the information of its transportation process from coastal area of Asian continent to central/eastern subtropical Pacific based on the samples collected by a neuston-net for pre-season survey of Pacific saury. The concentration and composition in terms of size, colour, shape and polymer type (determined with a Fourier transform infrared spectrophotometer) were determined for 77 stations and those data were analyzed in relations to the oceanographic parameters including water temperature, salinity, and current flow pattern on sea surface. In the study area, on average, 152,762 ± 459,807 pieces km^-2 of floating plastic debris was found, with a maximum of 3,914,195 pieces km^-2 and distribution was primarily influenced by the current system but the process to generate the high concentration area seemed to be different between western and eastern area of the transition region. In the west of 180º, floating plastic debris largely accumulated around convergent in the nearshore area and transported by eddies and quasi-stationary jet to the subarctic region. Furthermore, in addition to the effect of Stokes drift, floating plastic debris retained by the anti-cyclonic eddies (warm core rings) may be kept remained within the coastal area due to its westward migration. Meanwhile some plastics like styrene foam and lines seems to be selectively eliminated from water column and decrease towards offshore. The average of the western area (68,575 ± 74,734 pieces km^-2) was 15 % higher than previously reported value in 1989, suggesting the possible increase of plastic debris during this 30 year. In the east of 180º, floating plastic debris accumulated in the calm water area corresponds to the downstream of the Kuroshio Bifurcation, a northern branch of the Kuroshio Extension. The concentration (505,032±991,989 pieces km^-2) was considerably higher than in the western area, implying that the heavily polluted area of floating plastic debris in the central subtropical North Pacific is larger than our prediction. The high concentration seemed to be related with intensification of surface accumulation of small-sized transparent film caused by calm weather condition in this area, suggesting the importance of further investigation focusing on small-sized plastic (< 1mm) including film type in the subsurface depth in the subtropical central/eastern Pacific.