Impact of Microplastics on Antarctic Krill Faeces Carbon Sequestration in the Southern Ocean

The Southern Ocean plays a crucial role in absorbing carbon dioxide from the atmosphere, accounting for 20% of the ocean's carbon sink despite covering only 10% of the global ocean area. Antarctic Krill (Euphausia superba) are central to this process, as their faeces help remove carbon from the upper ocean by sinking to deeper layers. However, microplastics are increasingly polluting the Southern Ocean, and have been found in zooplankton, especially krill. These buoyant microplastics may slow the sinking of krill faeces, potentially reducing the amount of carbon that is trapped in the deep ocean. Whether, and to what extent, microplastics impact faeces sinking is still an open question. To address this gap, we developed a theoretical model to study how microplastics affect the density and fragmentation of krill FP which in turn will impact their vertical sinking to the oceanic depths. Our findings suggest that in environmentally relevant concentrations, microplastics could slow down the sinking of these pellets. Larger microplastics have the most impact, causing greater fragmentation of the faeces as they settle in the water column. While the buoyancy effect of microplastics is currently marginal due to the density change, under a business-as-usual scenario. Our results highlight that future increases in microplastics will likely have a significant negative impact on the ability of krill to promote the storage of carbon in the deep ocean.