The team of scientists who conducted the study discovered around 1.9 million pieces of plastic in one square meter on the bottom of the Mediterranean Sea.
Microplastics are small pieces of plastic that are less than 5 millimeters in length and pollute the environment.
By studying sediment samples and deep ocean currents, scientists were able to determine that currents are distributing microplastics in concentrated locations across the seafloor, creating microplastic hotspots.
"These currents build what are called drift deposits; think of underwater sand dunes," co-lead author of the study Dr. Ian Kane told the BBC. "They are among the largest sediment accumulations on Earth. They're made predominantly of very fine silt, so it's intuitive to expect microplastics will be found within them."
The millions of microplastics on the bottom of the Mediterranean originated from clothing and other textiles that have eroded over time and likely entered the ocean through wastewater treatment plants.
Deep ocean currents also carry nutrients and oxygenated water, putting deep-sea creatures and ecosystems at risk of absorbing or ingesting plastic.
This study is the first direct link between current pattern behavior and high concentrations of microplastics on the ocean floor.
Scientists hope their research will help lead them to other potential hotspots on the ocean floor, so they can clean up the ocean and further study the impact of microplastics on marine life.