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Kai Ziervogel
Research Assistant Professor
Biogeochemistry/Microbial Ecology
Ph.D.,Marine Biology Baltic Sea Research Institute Warnemünde, University of Rostock, Germany

My research focuses on heterotrophic microbial cycling of organic matter in the ocean. This research is key to understanding food web interactions and the marine carbon cycle as heterotrophic microbial communities transform photosynthetically produced dissolved organic matter (DOM) into biomass, providing food sources for higher trophic levels. The fraction of the DOM that escapes immediate microbial processing often forms gel-like particles (marine polymer gels) acting as glue for sinking aggregates of organic and inorganic matter, also called marine snow. Marine snow aggregates are often densely colonized by highly active heterotrophic microbial communities, making them hotspots for the marine carbon cycle. Moreover sinking marine snow is responsible for the major downward flux of biologically fixed atmospheric carbon, accelerating carbon sequestration in the deep sea. A main aspect of my research is determining how the efficiency of heterotrophic microbial communities to access and degrade organic matter is affected by the formation of marine snow.

Current research projects:

1. Marine snow formation under small scale turbulence (NSF Chemical Oceanography)

Small scale turbulences are ubiquitous in the surface ocean, affecting nutrient fluxes and thus microbial growth and metabolism as well as aggregation and disaggregation of organic matter. This interdisciplinary project uses mesocosms that facilitate small scale turbulences (oscillating grids, rotating cylinders) to study microbial growth and metabolism, dynamics of polymer gels, and their role as glue for marine snow under changing turbulent conditions. We aim to develop an improved numerical model for carbon flux in the ocean that accounts for the effects of water mixing on marine snow formation.

My role: Co-PI and mentor to Wilton Burns (Master's student at UNH) Collaborators: Brian White (lead PI) and Adrian Marchetti (both University of North Carolina - Chapel Hill).

2. Effects of marine snow and associated microbial activities on chromophoric dissolved organic matter (CDOM) dynamics in the ocean (NSF Chemical Oceanography)

CDOM is an important fraction of the marine carbon cycle that controls most light absorption and many photochemical and biological processes in the ocean. Despite its importance, the chemical basis for the formation of oceanic CDOM remains unclear. We test the hypothesis that marine snow aggregates are hotspots for planktonic CDOM (i.e. microbially-transformed phytoplankton organic matter), using laboratory incubations and field observations.

My role: Co-PI Collaborators: Chris Osburn (lead PI) and Astrid Schnetzer (both NC State University), Thomas Bianchi (University of Florida).

3. The role of marine "oil" snow in the fate of petroleum hydrocarbon in the ocean (as part of the research consortium "Ecosystem Impacts of Oil & Gas Inputs to the Gulf of Mexico - ECOGIG" funded by the Gulf of Mexico Research Initiative)

DOM precursors of marine polymer gels are produced by a variety of planktonic organisms including heterotrophic bacteria capable of hydrolyzing petroleum hydrocarbons. Extracellular microbial polymers effectively emulsify crude oil, accelerating the bacterial oil degradation cascade in the ocean. They also enhance the formation of sinking marine "oil" snow (MOS), i.e. aggregates of weathered oil and planktonic particles. MOS represented a major sink of spilled oil and its byproducts to deep Gulf of Mexico environments following the Deepwater Horizon disaster in 2010. This project studies the formation of MOS, activities of MOS-associated heterotrophic microbial communities, and the fate of MOS in the deep sea (sedimentation and resuspension).

My role: Co-PI

Collaborators: Carol Arnosti, Andreas Teske, Chris Martens, Barbara MacGregor (all UNC), Samantha Joye (University of Georgia; Consortium Director), Uta Passow (University of California, Santa Barbara).

CV (Curriculum Vitae)