Production and diversity of microorganisms associated with sinking particles in the subtropical North Pacific Ocean

Abstract

Sinking particulate organic matter controls the flux of carbon (C) from the surface ocean to the deep sea. Microorganisms actively colonize particles, but the extent to which microbial metabolism influences particle export remains uncertain. We conducted experiments to quantify rates of bacterial production (derived based on 3 H-leucine incorporation) and dark C-fixation (based on 14 C-bicarbonate assimilation) associated with sinking particles collected from the base of the euphotic zone (175 m) in the subtropical North Pacific Ocean. Seawater was amended with sinking particles and rates of filter size-fractionated (0.2, 2, and 20 μm) bacterial production and dark C-fixation were measured. Sequencing of 16S ribosomal RNA (rRNA) gene amplicons revealed that microorganisms in the particle-amended treatments differed from those in the unamended seawater controls, with the particle treatments enriched in putative copiotrophic bacteria. The addition of sinking particles increased rates of bacterial production (by 6-to 9-fold), and to a lesser extent dark C-fixation (by 1.7-to 4.6-fold), relative to unamended controls, with most of the production associated with filter pore sizes < 20 μm. Normalizing production to concentrations of particulate C yielded rates that were statistically indistinguishable between particle-amended treatments and unamended controls. We then examined possible relationships between sinking particulate C flux attenuation and its supply to the mesopelagic waters, revealing that flux attenuation was positively related to increases in particulate C supply. Together with results from our experiments, we suggest processes that contribute to sinking particle disaggregation both increase flux attenuation and favor microbial mineralization of particle-derived organic matter.

Constraining the Particle Size Distribution of Large Marine Particles in the Global Ocean With In Situ Optical Observations and Supervised Learning

“…It captures regional and seasonal variability in observed PSD properties, and demonstrates the ability of statistical machine learning methods to extrapolate these quantities globally. These global PSD reconstructions can in turn shed light on processes that depend on, or are reflected by, particle abundance and size distribution, including sinking particle fluxes (Guidi et al., 2008), aggregation, disaggregation and degradation of organic particles (Briggs et al., 2020; Burd & Jackson, 2009), interactions with microbial communities (Church et al., 2021; DeLong et al., 1993) and migrating animals (Cram et al., 2022), and chemical exchange between particles and seawater, including element scavenging (Ohnemus et al., 2019).…”

“…Particles can be remineralized by microbial degradation and grazing by zooplankton (Karl et al., 1988; Giering et al., 2014; Steinberg et al., 2008), aggregate and disaggregate following physical and biological interactions (Briggs et al., 2020; Burd & Jackson, 2009; Dilling & Alldredge, 2000; Jackson, 1990; Kiørboe et al., 1990), and sink out of the surface layers to transfer carbon and nutrients to the ocean interior (Boyd et al., 2019; Buesseler et al., 2007; Turner, 2015). Marine particles are hotspots of microbial activity and diversity (Church et al., 2021; DeLong et al., 1993; Karl et al., 1984), provide the bulk of energy that sustain mesopelagic and abyssal ecosystems (Burd et al., 2010; Giering et al., 2014), and eventually supply materials to the ocean sediment, where burial sequesters them for geological timescales (Dunne et al., 2007; Sarmiento & Gruber, 2006).…”

Sediment Trap Study Reveals Dominant Contribution of Metazoans and Dinoflagellates to Carbon Export and Dynamic Impacts of Microbes in a Subtropical Marginal Sea

“…The Flavobacteriaceae alone could account for up to 7.74% of the total prokaryotic community at station C9. Similarly, studies in other areas also showed that many taxa in Gammaproteobacteria and Flavobacteriales were dominant in the sinking community (Baumas et al., 2021; Church et al., 2021). Systematic assessment of individual prokaryotic lineage's contribution in carbon export is also warranted.…”

Microbes contribute to setting the ocean carbon flux by altering the fate of sinking particulates

“…However, these large-scale models have not explicitly included microbial ecological dynamics. This is problematic as many of the aforementioned physical and chemical mechanisms shown to impact the vertical flux of POC are controlled by microbial and grazer dynamics 22 – 25 , 30 . For example, lability as represented by these models is inherently related to microbial activity (as we demonstrate below).…”

“…These micro-scale observations suggest that the rate of POC consumption in the ocean is highly variable and can vary as a function of microbial processes, in contrast to the conventional representation in carbon cycle models 45 , 46 , 53 , 57 , 58 . Therefore, to mechanistically understand the vertical flux of carbon in the ocean and generate robust predictions of future changes, we must account for particle-associated microbial behavior 22 , 24 , 59 , in addition to other dynamics such as particle size distribution and zooplankton activity.…”