From Carbon to Plastics: Partitioning of Biogeochemical and Anthropogenic Particles in Penguin Guano

Penguins are emblematic inhabitants of the Antarctic continent and play a significant role in the biogeochemical cycles of the Southern Ocean by transferring essential nutrients to marine ecosystems via guano production. Despite their ecological importance, the contribution of penguin guano to carbon cycling remains largely unexplored. Microplastics (MPs) add complexity to these dynamics. MPs in fecal material can limit carbon export by reducing sinking rates and increasing remineralization. We examined guano from two penguin species, the Chinstrap (P. antarcticus) (n = 25) and Gentoo (P. papua) (n = 7), from the South Shetland Islands. We quantified biogeochemical particulate components (carbon, nitrogen, and biogenic silica) and characterized MP polymeric composition. Both species showed similar values for natural particulate fractions. Microplastics were detected in 91% of samples, dominated by small particles (25–50 μm, 46%). Chinstrap guano contained the highest amount of MPs. Polypropylene was the predominant polymer (34% in Chinstrap, 75% in Gentoo), followed by polyethylene (37% in Chinstrap, not found in Gentoo). This study provides the first survey of the smallest MP fraction (down to 25 μm) in penguin guano, offering new insight into how a shift in the partitioning from natural to MP particles, previously overlooked, may influence guano-mediated carbon pathways.