Microplastic sediment sinks
Microplastics and their potential impacts on life on Earth have been the subject of increasing focus in recent years. Of particular interest are the ‘missing’ marine microplastics
Microplastics and their potential impacts on life on Earth have been the subject of increasing focus in recent years. Of particular interest are the ‘missing’ marine microplastics – those unaccounted for when comparing estimates of plastic inputs to the global ocean to the volumes observed in the ocean surface, where plastics are unexpectedly low in abundance.
Previous analysis has shown that as much as 88% of all plastics that have entered the ocean since 1950 may have accumulated in ocean sediments, but this estimate is disputed.
To address this debate, Seung-Kyu Kim at Incheon National University, Republic of Korea, and colleagues, sampled marine sediment and seawater from two regions in the western Arctic Ocean – in the north where sea ice melts and forms annually, as well as the southern ice-free region.
To reduce the risk of microplastic contamination affecting the results, the team were careful to remove those parts of the samples that were exposed to air or plastic during the sampling process, and to use a stainless-steel spoon to handle the remainder of the samples.
The results show that Arctic sediments are a significant sink for microplastics currently and will continue to be in the future, with microplastic deposition increasing by 3% every year. The team also found that deposition is enhanced around the sea ice retreat line, implying that the ice barrier facilitates greater transport of microplastics vertically from the seawater to the underlying seabed. The rate of microplastic burial in sediments lags its delivery to the ocean, implying that microplastics will continue to accumulate in ocean sediments even if plastic production is immediately halted.
Sci. Adv. 9, eadd2348(2023); doi:10.1126/sciadv.add2348