The accumulation of microplastics in the world-s oceans has been all over the media since the discovery of the Great Pacific Garbage patch in 1997. Although the impacts of plastics on the marine ecosystem and the amounts in the gyres have by now been quite extensively covered in literature, research regarding the journey of the plastic debris from source to sink is still scarce. Consequently, this thesis aims to identify the major pathways of synthetic polymers from anthropogenic sources to the 5 accumulation zones in the oceans, including closer scrutiny on how the Tohoku tsunami of 2011 impacted the flows and stocks. The results are based on thorough literature review and are presented as a global material flow analysis (MFA) to point out the extent to which each source contributes to the prevalence of plastic in the five gyres of the world's oceans. The presentation of the results as an MFA aims to support future policy-making and provide research incentives in marine pollution prevention. The research shows that of the 285Mt of plastics produced in 2014, 4.76Mt entered the marine environment as beach litter, depositions on the seafloor and microplastics in the gyres. The main flows towards the gyres were identified as 0.4Mt/year extra-gyral input of beach litter as well as 0.3Mt/year inflow from anthropogenic pre-and postconsumer plastic stocks in the case of a tsunami. The flow of litter towards the beach stemmed mainly from uncollected plastics, amounting to 0.56Mt/year, and dumpsite leaking, equaling 4.19Mt/year as of 2014. The study further showed that the shipping industry and related export activities have only a minor impact on the plastic abundance in the ocean, with an input of a mere 0.044Mt/year. Additionally, the comparison between every year flows and tsunami induced flows showed a doubling of the input to the gyres caused by a single event in one region of the world. This underlines the role of efficient waste management prior to the event, as well as quick disaster response, in reducing the input of plastic material to the gyres. The overwhelming scarcity of data in this section of marine debris research made it necessary to base a substantial part of this thesis on extrapolation and estimations: It is therefore concluded that further research needs to be done to properly quantify the different flows of plastic to the ocean and identify the most efficient way in preventing plastic from damaging the marine ecosystem.