Microbial and hydrothermal controls on organic carbon mobilization from Guaymas Basin sediment

Organic carbon stored in marine sediments and sedimentary rocks are a critical component of the global carbon cycle. This project investigates organic carbon in marine sediments and examines its bioavailability to microbes. The setting for the project is the Guaymas Basin of the Gulf of California which receives organic matter inputs from land during seasonal rains and from marine phytoplankton at the sea surface. Guaymas Basin is also a site of active seafloor spreading and hydrothermal heating which will allow the effects of heating on the bioavailable fraction of organic carbon to be investigated. The goals of this project are to investigate the effects of hydrothermal heating, burial depth (physical factors), sedimentary organic carbon composition and oxygen availability (geochemical factors) and microbial community (biological factors) on the bioavailability and mobilization/utilization of sedimentary organic carbon. Results from this project will improve our understanding of how microbes reintegrate this subsurface organic carbon back into the “active” carbon cycle, as well as how this microbial activity is influenced by hydrothermal heating and organic carbon composition.

Funding: NSF Chemical Oceanography & Marine Geology & Geophysics

Collaborator: N. Mahmoudi (McGill)

Seasonal controls on biomarker and microbial diversity in the tidally-influenced outlet of the Broadkill River

Decades of research have been devoted to understanding the microbial players that contribute to primary productivity and drive the heterotrophic degradation of organic matter in the shallow estuarine and oceanic waters that account for almost half of global net primary productivity. In this project we seek to characterize key microbial players and how they vary with season and tidal stage.

Funding: University of Delaware Research Foundation

Collaborator: J. Biddle (UD)


Understanding microbial carbon cycling beneath the seafloor during cool hydrothermal circulation

The oceanic subsurface comprises a vast and varied microbiome. This project investigates the largest actively flowing aquifer system on Earth – the fluids circulating through the rocky oceanic crust underlying the oceans and sediments. It is a collaborative project that combines microbiological and organic geochemical approaches to describe the linkages between microbial activity and the cycling of organic carbon in the cool, subseafloor biosphere. In particular, we focus on the impact microbial activity has on the dissolved organic carbon reservoir in the crust and on the balance between heterotrophic (organic carbon-consuming) and chemoautotrophic (organic carbon-producing) metabolisms within the cool crustal biosphere using isotope geochemical and molecular biological approaches. This project focuses on fluids recovered from seafloor observatories put in place by the International Ocean Discovery Program (IODP) at North Pond, a sediment pond on the western flank of the mid-Atlantic Ridge. This site is likely representative of the majority of global hydrothermal fluid circulation. Results will help establish the extent to which microbially-mediated processes in the subseafloor influence carbon cycling in the ocean.

Funding: NSF Biological Oceanography

Collaborators: P. Girguis (Harvard), J. Huber (WHOI), H. Osterholz, E. Trembath-Reichert (ASU), T. Dittmar (U. Oldenburg)