A focus on different types of organic matter particles and their significance in the open ocean carbon cycle

Marine particles are key to the cycling of major elements on Earth and play an important role in the balance of nutrients in the ocean. Three main categories ofmarine particles link the different parts of the open ocean by shaping carbon distribution: (i) sinking; (ii) suspended, and (iii) ascending. Atmospheric carboncaptured by phytoplankton in the surface water, is partly sequestered by sinking particles to the bottom of the ocean and plays an important role in controlling globalclimate. Suspended particles represent a significant source of organic carbon for heterotrophic microorganisms and are more likely to undergo remineralizationcompared to sinking particles. Ascending particles, depending on their composition, point of origin, and ascending velocity, may lead to carbon remineralization inthe upper layers of the ocean in closer proximity to the atmosphere. Marine particles are hotspots of microbial activity and thus heavily colonized by microorganismswhose dynamics play an important role in organic matter degradation, aggregation and sinking, thus directly influencing the biological carbon pump efficiency.Microbiomes of marine particles differ depending on particle size, source, and age. Nevertheless, these factors are generally overlooked, and particles are mostlystudied as “bulk” without considering the high heterogeneity between individual particles. This hinders our understanding of the carbon budget in the ocean and thusfuture predictions of climate change. In this review we examine known particle-types and associated sampling methods and identify knowledge gaps and emphasizethe need for a better understanding of the single-particle ecosystem to enhance global upscaling rates. Furthermore, we introduce a novel concept: the ‘lipid carbonshunt’.