Microbially mediated elemental cycles

Microorganisms are too small to see with the naked eye without magnification. They are the dominant organisms in the ocean in terms of mass, diversity, and ecological importance. We determine rates and activities of microbially mediated cycling of organic matter and nutrients in the water and in sediments in a wide variety of aquatic environments. Our goal is to better understand microbial metabolic responses to anthropogenic impact on aquatic environments such as eutrophication, ocean acidifaction and warming.

Marine snow and associated microbial processes

Marine snow forms in surface waters when microbial cells (dead or alive) collide with other suspended detrital material and mineral particles. Loaded with freshly produced organic matter, these aggregates are densely colonized by active bacteria that respire the organic fraction of the snow particle. We study the formation, sinking, and fragmentation of marine snow as well as bacterial colonization and metabolic activities in and around sinking aggregates. We also investigate the role of marine snow as transport vehicles for ocean contaminants (oil and plastics). Our work aims to improve the underlying biological and physical processes that determine the fate of marine snow in the water column.

Microbial activities in the deep-sea

The mean depth of the ocean is 3800 m. Depths below 200 m are generally classified as the deep-sea that takes up 93% of space of our entire planet. The deep-sea is characterized by permanent darkness, cold temperatures, and high hydrostatic pressure conditions. More than half of the marine prokaryotic biomass and heterotrophic production is found in the deep-sea; however, microbial processes below the well-lit surface ocean are not well defined. We investigate microbial growth and cycling of particulate (sinking) and dissolved (non-sinking) organic matter cycling in meso- and bathypelagic waters to improve our understanding of deep-sea microbial food webs. So far, our work has taken us to the deep Gulf of Mexico, Gulf of California, Northeast Pacific, and North Atlantic.

Benthic-pelagic coupling

Benthic-pelagic coupling is a concept in which seafloor processes affect pelagic environments through transport of dissolved and particulate matter from the sediment into the overlying water column. We study these processes in shallow coastal waters, lakes as well as the deep ocean, using erosion chambers and in situ observations. Our goal is to better understand the effects of benthic-pelagic coupling on microbially mediated cycling of organic matter and nutrients in the water.