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 (April 27th – May 19th 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 ATR-FTIR (≥ 315 μm) and μFTIR (10–315 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.

This research was supported by the i-plastic project (PCI2020-112059 — JPI-Oceans) and contributed to ICTA-UAB's María de Maeztu Programme for Units of Excellence of the Spanish Ministry of Science and Innovation (CEX2024-001506-M — MICIU/AEI /10.13039/501100011033) and the Marine and Environmental Biogeosciences Research Group (MERS; 2021SGR00640 — Generalitat de Catalunya). S.B. was supported by the FI-AGAUR PhD scholarship (2022 FI_B 00359 — Generalitat de Catalunya).