BRIN: Microplastics Penetrate to 2,450-Metre Depth in the Indonesian Throughflow
Microplastics have long been associated with plastic waste floating on the ocean surface or accumulating along coastlines. However, new findings paint a much more alarming picture: particles smaller than five millimetres have been found to penetrate the deep sea to depths of around 2,450 metres.
The discovery comes from a study published in the international journal Marine Pollution Bulletin (2024) titled Vertical Distribution of Microplastic Along the Main Gate of Indonesian Throughflow Pathways. The study was led by Corry Yanti Manullang, Senior Researcher at the Centre for Deep Sea Research, National Research and Innovation Agency (BRIN), in collaboration with teams from Indonesia, Malaysia, the United States, and China.
The research reveals that microplastics are not confined to the surface layer but are distributed throughout the water column along the main channel of the Indonesian Throughflow (Indonesian Throughflow/ITF), also known as Arlindo.
According to Corry, the role of Arlindo is not merely to move water masses.
“Arlindo connects two great oceans, the Pacific and Indian Oceans. In addition to carrying water masses, salt, and nutrients, this current also has the potential to transport small particles such as microplastics,” Corry said.
Until now, studies of Arlindo have focused more on physical oceanographic aspects such as temperature, salinity, and current dynamics. The vertical distribution of microplastics in the water column—particularly into the deep sea—has been less studied.
“This study is one of the early investigations into the vertical distribution of microplastics down to the deep sea along the Arlindo corridor. Up to now, much microplastic research in Indonesian waters has concentrated on the surface layer or coastal areas,” she said.
A total of 92 water-column samples were collected from depths ranging from 5 metres to around 2,450 metres. The samples were taken using a rosette sampler linked to a CTD (Conductivity, Temperature, Depth) system, allowing precise sampling at specific depths.
“The sample bottles are lowered into the sea and closed at depths that have been predetermined, for example 50 metres, 200 metres, to thousands of metres,” Corry explained.
From a total of 872 litres of seawater analysed, the researchers found 924 microplastic particles. The average concentration reached 1.062 particles per litre. Surprisingly, microplastics were found at all study stations, including depths exceeding two kilometres below the sea surface.
The analysis showed that more than 90 per cent of the microplastics were fibre-shaped, typically originating from synthetic textiles.
“The clothes we wear can also generate microplastics. When washed, tiny fibres from synthetic fabrics can shed and eventually enter the water system,” Corry noted.
Through Raman spectroscopy analysis, the team identified several polymer types such as polyester, polypropylene, and polyurethane—materials widely used in textiles, packaging, and industrial products.