Weight and count data was collected by trawling nets for microplastics and using systematic visual sightings for the larger macroplastics.
Using this data we calibrated a numerical model that assumes plastic entering the oceans from rivers, shipping lanes and densely populated coastlines.
To visualise the model-predicted concentration, we produced an interactive map that shows the weight density estimates as a dot density map, where each dot represents 20 kg of floating plastic, totalling more than 13 million dots globally.
We calculated the number of dots for each model cell -an area of around 400 km²- and randomly distributed them within each cell using a circular Gaussian function.
The map also displays the different expeditions that participated in the data collection effort from 2007 to 2013.
For each individual expedition stage, heatmaps show the measured plastic densities for every survey location (horizontal axis) and four classes of debris size (vertical axis). They are available for weight and count densities, as well as for the corresponding model estimates.
The four size classes roughly correspond to the sizes of a grain of sand, a grain of rice, a small water bottle and anything larger.
Based on conservative fragmentation rates, researchers originally expected to find more small particles than larger ones, but this study surprisingly shows that the smallest fragments are generally less abundant than the second smallest size, but are often found in remote regions outside of the garbage patches..
"Our findings show that the garbage patches in the middle of the five subtropical gyres are not final resting places for floating plastic trash,"the study's lead author, Dr Marcus Eriksen said.
"Unfortunately, the endgame for microplastic is dangerous interaction with entire ocean ecosystems. We should begin to see the garbage patches as shredders, not stagnant repositories."
Read the research paper here:
