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

Abstract

Sinking particulate organic carbon out of the surface ocean sequesters carbon on decadal to millennial timescales. Predicting the particulate carbon flux is therefore critical for understanding both global carbon cycling and the future climate. Microbes play a crucial role in particulate organic carbon degradation, but the impact of depth-dependent microbial dynamics on ocean-scale particulate carbon fluxes is poorly understood. Here we scale-up essential features of particle-associated microbial dynamics to understand the large-scale vertical carbon flux in the ocean. Our model provides mechanistic insight into the microbial contribution to the particulate organic carbon flux profile. We show that the enhanced transfer of carbon to depth can result from populations struggling to establish colonies on sinking particles due to diffusive nutrient loss, cell detachment, and mortality. These dynamics are controlled by the interaction between multiple biotic and abiotic factors. Accurately capturing particle-microbe interactions is essential for predicting variability in large-scale carbon cycling.

Formulation, optimization and sensitivity of NitrOMZv1.0, a biogeochemical model of the nitrogen cycle in oceanic oxygen minimum zones

“…Because of the low abundance of organic matter in seawater, and extensive colonization of particles by heterotrophic bacteria, this is a reasonable first order assumption. However, see Nguyen et al (2022) for a discussion of microbial-particle interactions in ocean biogeochemical models, and more complex aspect of their dynamics. For simplicity, we represent organic carbon by a single component.…”

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

“…Particle dynamics is also central to Earth System Models used to describe ocean biogeochemistry and the carbon cycle, and project their future change (Bopp et al., 2013; Kwiatkowski et al., 2020). While current ocean biogeochemical models include at most few size classes (Séférian et al., 2020), explicit representation of PSD has emerged as a powerful and promising approach to mechanistically represent size‐dependent processes and their influence on elemental cycles, carbon sequestration, and ecological interactions in the ocean (Burd & Jackson, 2009; Cram et al., 2018; Devries et al., 2014; Gehlen et al., 2006; Kriest & Evans, 1999; Nguyen et al., 2022; Omand et al., 2020; Stemmann et al., 2004; Weber & Bianchi, 2020). However, quantifying the large‐scale abundance, distribution, and size structure of marine particles has been historically difficult.…”

“…To first order, size controls particle elemental composition (Alldredge & Gotschalk, 1988), aggregation and disaggregation rates (Briggs et al., 2020; Burd & Jackson, 2009), and the ability of particles to sink (Alldredge & Gotschalk, 1988; Cael et al., 2021; McDonnell & Buesseler, 2010), thus providing a first order influence on the ocean's biological pump (Boyd et al., 2019). Furthermore, size‐dependent properties such as particle volume and surface area affect interactions with microorganisms, including colonization, metabolism, and particle degradation (Bianchi et al., 2018; Jackson, 1989; Kiørboe et al., 2002; Nguyen et al., 2022), and coupling with seawater chemistry via regeneration of elements (Broecker & Peng, 1982; Sarmiento & Gruber, 2006), adsorption, and scavenging processes (Ohnemus et al., 2019; Turekian, 1977).…”

Porous marine snow differentially benefits chemotactic, motile, and nonmotile bacteria

“…A recent study highlighted the importance of flow for the degradation dynamics of marine particulate organic matter ( 57 ). In this study, we look at the encounter and attachment of bacteria to marine particles (the sum of these processes describing successful colonization) that represent the first step of particle remineralization, and a mechanistic understanding of these processes is thus crucial to advance our predictive capabilities ( 58 ). Our study confirms that motility is the key trait that enables particle colonization, but further provides insights how chemotaxis facilitates particle colonization during the brief window of opportunity by enabling to rapidly navigate the particle boundary layer.…”