The deep sea is a major sink for microplastic debris. Microplastics, particularly fibres, were found to be up to four orders of magnitude more abundant in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea, and Indian Ocean than in contaminated surface waters. This study shows that the deep-sea floor may hold a large, previously unknown repository of microplastics. The dominance of microfibres suggests a previously underreported and unsampled plastic fraction. The vastness of the deep sea and the prevalence of microplastics at all investigated sites indicate that the deep-sea floor may be the answer to where all the plastic is. The study involved a global analysis of deep-sea sediment samples collected by two independent research teams during seven cruises between 2001 and 2012. The samples were processed and analysed to quantify the abundance and extent of microplastic contamination at various depths and locations. Microplastics were identified using FT-IR spectroscopy, revealing that they were predominantly fibres, with rayon being the most common type. The study highlights the ubiquity of microplastics in the deep sea and suggests that their accumulation is complex and influenced by various domestic and industrial sources. The findings indicate that the deep sea may act as a sink for microplastics, with significant implications for marine ecosystems. The study also underscores the need for consistent methodologies to better understand the transport, accumulation, and spatial distribution of microplastics, as well as their potential environmental impacts.The deep sea is a major sink for microplastic debris. Microplastics, particularly fibres, were found to be up to four orders of magnitude more abundant in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea, and Indian Ocean than in contaminated surface waters. This study shows that the deep-sea floor may hold a large, previously unknown repository of microplastics. The dominance of microfibres suggests a previously underreported and unsampled plastic fraction. The vastness of the deep sea and the prevalence of microplastics at all investigated sites indicate that the deep-sea floor may be the answer to where all the plastic is. The study involved a global analysis of deep-sea sediment samples collected by two independent research teams during seven cruises between 2001 and 2012. The samples were processed and analysed to quantify the abundance and extent of microplastic contamination at various depths and locations. Microplastics were identified using FT-IR spectroscopy, revealing that they were predominantly fibres, with rayon being the most common type. The study highlights the ubiquity of microplastics in the deep sea and suggests that their accumulation is complex and influenced by various domestic and industrial sources. The findings indicate that the deep sea may act as a sink for microplastics, with significant implications for marine ecosystems. The study also underscores the need for consistent methodologies to better understand the transport, accumulation, and spatial distribution of microplastics, as well as their potential environmental impacts.