A global dataset of ocean plastic pollution between 1979 and 2019 has been collated by Marcus Eriksen and colleagues from non-profit group The 5 Gyres Institute.
Improved understanding of plastic accumulation in the oceans to date could provide a "critical baseline" to help address this form of pollution, the researchers said.
Previous studies have focused primarily on northern-hemisphere oceans near the world's most industrialised nations, while other studies have found increases in ocean plastic over shorter time periods.
In this study, the researchers looked at data on ocean-surface-level plastic pollution collected between 1979 and 2019 from 11,777 stations across six marine regions (North Atlantic, South Atlantic, North Pacific, South Pacific, Indian and Mediterranean).
After accounting for wind, site selection and biases due to under-sampling, the model showed a significant and rapid increase since 2005 of the global ocean abundance and distribution of plastics in the ocean surface layer.
An estimated 171 trillion plastic particles, primarily microplastics, weighing around 2.3 million tonnes were afloat in 2019.
A relative lack of data from 1979 to 1990 prevented trend analysis during this period, while between 1990 and 2004 plastic levels showed fluctuations with no clear trend.
Though these results are biased towards trends in the North Pacific and North Atlantic, where the majority of the data was collected, the researchers suggest the rapid increase from 2005 reflects the global growth of plastic production, or changes in waste generation and management.
Without widespread policy changes, the study suggests the rate at which plastics enter our waters will increase approximately 2.6 times by 2040.
Marcus Eriksen, co-founder and researcher from The 5 Gyres Institute, adds: "We've found an alarming trend of exponential growth of microplastics in the global ocean since the millennium, reaching over 170 trillion plastic particles. This is a stark warning that we must act now at a global scale. We need a strong, legally binding UN Global Treaty on plastic pollution that stops the problem at the source."
Last month, another team developed a technique to easily track microplastics from space using satellites.
