Enhanced production of dissolved and particulate organic matter in the presence of microplastics at the air-sea interface

The ubiquitous presence of microplastics in marine habitats has potential impacts on biogeochemical cycling as well as ecological consequences across trophic levels. Microplastics provide increased surface area for microbial growth, with consequences on carbon and nutrient dynamics at the basis of all marine food webs. Despite their high and increasing concentration in the ocean, microplastics’ influence on the transformation and composition of marine organic matter is largely unknown.

In the POSEIDOMM project (www.poseidomm.eu), we are exploring the impact of microplastics on the microbial processing of both dissolved and particulate organic matter in controlled marine conditions. Studies have been completed in a series of laboratory microcosms investigations and in a large scale outdoor mesocosm experiment.

The initial results indicate that the presence of standard polystyrene microbeads increased the production of dissolved (microcosms) and particulate organic matter (mesocosms) and their accumulation at the air-sea interface. This increase could result from either higher microbial production or enhanced transformation of pre-existing substrates. In the upper 100 µm of the mesocosms’ surface, we also observed a higher accumulation of marine gels which led to a modified surface film, with consequences on the air-sea exchange of oxygen and CO₂. Given their low density and wide distribution, microplastics present an elevated potential to influence the dynamics of the upper ocean.