Microplastic (MP) contamination of the open ocean is well documented, yet the vertical structuring of MPs and the role of water masses in shaping deep-water inventories remain poorly resolved along the eastern boundary of the North Atlantic Subtropical Gyre. Here we present a high-resolution vertical profile of MPs in the Canary Basin, based on discrete water samples collected during the MSM/127 cruise (R/V Maria S. Merian, March 2024) at three offshore stations south of Gran Canaria, comprising one full-depth profile (seven depths, 5 to 2720 m) and two stations sampled at shallower horizons; consequently, the deep-water structure below 1500 m reflects a single-station profile and should be interpreted as indicative rather than basin-wide representative. Particles were characterised by stereomicroscopy, ATR-FTIR, micro-Raman spectroscopy and SEM-EDX. MPs were detected in 100% of samples (n = 33), with a mean abundance of 19.5 ± 14.9 MP L-1, the large dispersion reflecting a markedly non-monotonic vertical distribution: a subsurface maximum of 39.3 ± 4.0 MP L-1 at 500 m, coinciding with the upper boundary of the North Atlantic Central Water and the top of the regional Oxygen Minimum Zone; a vertical minimum of 2.0 ± 1.0 MP L-1 at 2000 m; and a secondary deep-water signal between 2500 and 2720 m. MP abundance was strongly correlated with temperature (Pearson r = +0.77), salinity (r = +0.66) and potential density (r = -0.76; all p < 0.001), whereas its association with dissolved oxygen was weak and non-monotonic (Spearman ρ = -0.06, ns), consistent with water-mass structure, rather than dissolved‑oxygen levels, as the principal physical correlate of MP vertical distribution. With depth, the assemblage converged toward fine (<500 μm), dark, fibrous polyethylene terephthalate (PET) particles, reaching 100% PET between 1500 and 2720 m. SEM-EDX revealed weathered, biofouled surfaces bearing Saharan mineral and biogenic carbonate residues, consistent with a Saharan dust and biogenic origin, suggesting that the deep Canary Basin acts as a potential accumulation zone delivering an aged PET-fiber signature to abyssal layers.
🌊
