Microlitter distribution from tropical to temperate regions of the Atlantic Ocean was assessed using the pump-underway ship intake system. Sampling was performed during the PYROWIND oceanographic campaign in the Atlantic Ocean (27th of April 2022 – 19th of May 2022), on board of the Spanish R/V Hespérides. The research cruise covered an 8,000-km transect, from Brazil (Salvador) to the Strait of Gibraltar. Subsurface water samples were continuously collected through the pump-underway ship intake system during navigation. The water was collected by a pump (BKMKC.1011, TECNUIM) with a Teflon core located in the keel of the vessel at about 4.5 m deep, with a flow rate of 4 m³/h. The pump-underway system had a tap connection to the wet laboratory, to which the filtering device was connected to a hose. The filtering device consisted of a flowmeter attached to a funnel, which enclosed a 63 μm stainless-steel sieve, in order to avoid airborne contamination. The flow ran 24/7 and was divided into samples of 4.15 ± 1.47 m³ (10 L/min; n = 52). Particles were quantified and analyzed using μFTIR (10–315 μm) and ATR-FTIR (≥ 315 μm). The data were used to identify microlitter hotspots in the Atlantic Ocean and to model the probable pathways and sources of the particles. Sample collection was halted when the vessel stopped for standard cruise sampling, to avoid contamination from any equipment deployed at sea. Field and procedural blanks were performed to assess possible sample contamination.

i-plastic project is funded by JPI-Oceans through support by the national funding agencies: Brazil: Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP); Italy: Ministero dell'Università e della Ricerca (MUR); Portugal: Fundação para a Ciência e a Tecnologia; Spain: Agencia Estatal de Investigacíon (AEI; Project reference: AEI/10.13039/501100011033)