Microplastics prevail at all ocean depths of the HAUSGARTEN observatory (Arctic)

Although recent research indicates that microplastic (MP) has spread to all marine ecosystem compartments from the sea surface to the deep sea, our knowledge about the distribution through the water column is still limited and largely based on model runs. To fill this gap, we deployed WTS-LV large volume pumps at four different depths (sea surface, ~300m, ~1000m, near seafloor) at five stations of the HAUSGARTEN observatory (west of Svalbard). These pumps filtered 218–560 litres of seawater during each deployment with 10 µm mesh metal filters. Additionally, sediment was sampled at the same stations to understand accumulation mechanisms of MP in the sediment. Our analyses of water column samples using µFTIR spectroscopy resulted in 0–1373 MP m-3, comprising 15 different polymer types. MP concentrations in the sediment were found 1,200-33,000 times higher than in the water column. The northernmost station, which is located in the transition zone between the open ocean and sea ice, harboured the highest mean concentration (416 MP m-3) through the water column, and polyamide accounted for the largest proportion. The surface waters had the highest MP concentrations at all stations with a decrease towards the sediment. Our results will be compared with trends in the vertical distribution of organic particles and discussed in the context of prevailing water masses and sea ice coverage. Still, our preliminary results highlight that noticeable amounts of MP are present throughout the water column, Earth’s largest biome, which has been largely neglected in previous estimates of plastic in the world’s oceans.