Presenter: Trang Nguyen (University of Southern California)

Description:
Sinking particulate organic matter (POM) from the surface ocean sequesters carbon on decadal to millennial timescales. Predicting this flux is therefore critical for understanding both global carbon cycling and the climate. However, the microbial controls on POM degradation and the impact on the vertical POM flux remains poorly understood. Here we develop an ecological model that integrates microbial metabolic capacity, microbial population behavior, and dynamic marine environments to generate a mechanistic understanding of the key factors influencing the rates of particle degradation. The model captures observed POM flux attenuation profiles and provides a mechanistic explanation for the commonly used approximation of two labilities of POM or the double exponential representation of the POM flux. We show that enhanced transfer of carbon to depth can result from populations struggling to establish colonies on sinking particle due to loss processes including diffusion, cell detachment, and mortality. This work suggests that shifts in microbial communities both in surface waters and at depth can result in significantly different POM fluxes and that the magnitude of microbial driven variations in POM flux is similar to other, previously proposed, processes (e.g. particle size spectrum). Our results highlight the need for better in situ measurements of key biological processes such as loss processes for microbial communities, microbial abundance on particles, enzyme activities, growth rates on particles, and encounter and detachment rates for dominant particle-associated marine species.