Seminar Title: Biogeochemistry of marine particles in anoxic environments

 Abstract: Marine particles in the ocean have diverse composition, origin and physical properties. They drive the transfer of carbon and nutrients from the surface into the deep ocean and provide habitat and resources to microorganisms. In this seminar I discuss models and observations of sinking particles and their relation to global carbon cycles. In particular, I focus on the role of anoxic marine environments in modulating the break-down of marine snow and how this role might relate to global biogeochemical processes. 

\I will first present a mechanistic model of sinking particles that suggests that the size distribution of particles, water temperature and the presence of anoxic water all fundamentally affect carbon sequestration into the deep ocean, globally. I will next describe measurements of the physics, chemistry and biology of marine particles in the Eastern Tropical North Pacific (ETNP) Oxygen Minimum Zone (OMZ). These measurements suggest that carbon flux through OMZs is high because particles of all sizes break down slowly in anoxic water, rather than because anoxia inhibits particle breakdown by zooplankton. I will also present evidence that particles are an important source of ammonium in the ETNP-OMZ that can drive nitrogen removal through the ANAMMOX process. Lastly, I will discuss some ongoing work in a profoundly different anoxic region, the Chesapeake Bay, where we are also investigating particle characteristics and biology. These findings provide insight into how particles and microorganisms interact in anoxic environments and the implications of these interactions for global processes.