Mapping micro- and nanoplastic particle abundance in the Western Baltic Sea, Cruise No. AL635 30.06.2025 – 11.07.2025 Kiel (Germany) – Kiel (Germany), PlastTrackBalt

The ocean is regarded as an important sink for plastic debris, the majority of which originates from land-based sources, due to, e.g. waste mismanagement. Within the marine environment, micro- and nanoplastic (MNP) particles are subject to transport processes on various temporal and spatial scales, which are also influenced by particle properties and interactions with marine biota and organic matter. The cruise AL635 PlastTrackBalt aims to map and quantify MNP pollution in the Western Baltic Sea, focusing on the Danish-German border region. Additionally, it will serve as proof-of-concept for new pre-concentration and analysis techniques developed for nanoplastic particles within the PlastTrack project. PlastTrack is funded as part of the Interreg program, which supports collaborations in the Danish-German border region. The PlastTrack cruise is being conducted by an international team from GEOMAR, the Alfred Wegener Institute (AWI), SDU Sønderborg, and the company Newtec. The mission focuses on sampling MNPs using a variety of advanced instruments. Floating microplastics are collected using a Neuston catamaran equipped with a 300 μm mesh net. Suspended MNP between 15 and 300 μm in size are sampled onto stainless steel mesh filters via pumping from depths of < 1 m or 6 m. To sample small MNPs, 100 L of the respective filtrate (< 15 μm) are enriched via cross-flow filtration (0.2–15 μm) using a setup developed at GEOMAR, while 50 L are filtered onto stainless steel sinter filters (0.5–15 μm). Suspended MNP are also sampled with the SubCtech microplastic sampler, which captures a broad range of particle sizes, from greater than 300 μm down to 30 μm. Sinking MNPs, often bound within marine snow, are retrieved using two high-volume (100 L) samplers known as Marine Snow Catchers. (Alkor-Berichte AL635)