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This study presents in situ, high-resolution optical measurements of particle size distributions (PSD) within sediment plumes generated by a pre-prototype deep seabed nodule collector vehicle operating in the abyssal Pacific Ocean. These measurements were obtained using a cutting-edge instrument, the LISST-RTSSV sensor. The data collected in situ reveal marked differences compared to previously reported laboratory-based, ex situ measurements. The grain size and other key particle shape characteristics are found to be dependent on multiple factors, including the collector vehicle maneuvers, the time elapsed following sediment discharge, and the complex hydrodynamic processes that generate the sediment in suspension. Significantly, the PSD from a highly complex succession of straight-line maneuvers converges to that of the canonical case of a simple straight-line driving maneuver within a timescale of ten minutes. Our results underscore the importance of parameterizing sediment plume transport models based on well-informed, comprehensive PSDs of detrained suspended sediment measured in situ at adequate timescales and in regions no longer strongly influenced by active and complex hydrodynamic processes.

The ocean’s biological carbon pump (BCP) comprises a set of physical and biological processes that impact how carbon is exchanged between the atmosphere, the land, and the ocean. Sinking particles, such as “marine snow,” are a key mechanism of the BCP, where the depth of remineralization of carbon from these particles governs the extent to which carbon releases back into the atmosphere or sequesters in the deep ocean (Siegel et al., 2021). In addition, this sinking flux is a key energy source for deep water and benthic ecosystems. Studying these particles remains challenging, however, making it difficult to quantify carbon flux on a global scale. Global climate change further decreases the predictability of oceanic carbon flux due to the indirect changes induced by warming, ecosystem shifts, and acidification. Other human-induced alterations of the ocean’s carbon cycle, such as proposed marine carbon dioxide removal (mCDR) techniques like ocean alkalinity enhancement or nutrient fertilization, stand to further complicate carbon quantification and the ability to establish a carbon flux baseline from which future measurements can be compared and contextualized.