20-11. Blue carbon fluxes and transformations in estuaries and the coastal ocean

CLOSED

----------

Background. Blue carbon stored in estuarine and ocean sediments is a massive reservoir of biologically reactive organic matter (OM). The exchange of blue carbon between sediments and the water column/atmosphere is a natural process that impacts the chemical balance of the oceans and estuaries, and the inventory of greenhouse gases (GHG) in the atmosphere. However, human-induced perturbations have the potential to accelerate the release of blue carbon, in some cases with troubling consequences for water quality and climate. For example, the size and scale of anoxic dead zones in oceans and estuaries is exacerbated by nutrient inputs from agriculture and wastewater that stimulate OM production followed by oxygen-consuming decomposition. OM decomposition also releases carbon dioxide (CO₂) and methane (CH₄) (the two most prevalent carbon-based GHGs) and dissolved organic carbon (DOC). If physical and biogeochemical conditions permit, the GHGs may be transferred to the atmosphere. In other cases where CH₄ and DOC are consumed by microbes, complex biological communities thrive, and production of CO₂ may alter seawater pH. The environmental and ecological impacts from the production and/or consumption of these carbon species depends on a multitude of poorly constrained physical, geological, chemical, and biological factors.

We seek a Mendenhall Fellow to investigate the production, transformation, and fate of CH₄, CO₂ and dissolved organic carbon (DOC) in methane-charged sediments in estuaries or continental margin methane seeps. Proposed studies should address the abiotic and biotic factors regulating elemental cycles (C, N, S, Fe, etc.) and fluxes associated with the biogeochemical transformation of blue carbon in the sediments, the water column, or both, and may include quantification of GHG fluxes across the air-water interface. Strategies include: 1) techniques to improve and develop methods for quantifying greenhouse gas exchange across the air-water interface, and/or 2) field observations, data-based modeling and lab-based experimental studies, or some combination thereof to identify active biogeochemical processes and microbial assemblages responsible for the chemical transformations. When applicable, the proposal will consider the effect of climate change and other anthropogenic effects.

Research Opportunity. Planned and proposed oceanographic expeditions in the Chesapeake Bay (CB) estuary, the Hydrate Ridge (HR) gas hydrate mounds, and eastern Black Sea (BS) hydrocarbon seeps are available to support the proposed research. The CB project will map GHG fluxes, collect sediment cores and sample the water column along the estuarine salinity gradient during periods that precede and correspond with the development of anoxic dead zones along the main stem of the bay. The HR gas hydrate mound study includes seafloor sampling with an ROV in a program designed to evaluate the production, flux, and fate of methane-derived DOC from seafloor gas seeps. The eastern BS hydrocarbon seep study is a proposed study that would quantify fluxes and microbial transformations of methane and hydrocarbons from the seafloor and to atmosphere. The applicant is encouraged to define a project that is complementary to these planned (CB and HR) and proposed (BS) studies.

For the past decade, the RAs have been developing analytical systems that utilize cavity ring-down spectroscopy (CRDS) to enable real time measurements of methane and CO₂ concentrations and stable carbon isotope ratios in near real-time in the field. With these systems, we can continuously map greenhouse gas fluxes (CH₄ and CO₂) across the air-water interface (Pohlman et al., 2017), and we can measure the concentrations and d¹³C of these gas from a variety of sample types (Pohlman et al., 2021).  We are also developing a CRDS-based system that permits non-destructive, repeated rate measurements of CH₄ and CO₂ consumption/production from as many as 16 serum vials. We encourage the applicant to utilize and improve these unique state-of-the-art capabilities. We also encourage the applicant to develop outside collaborations with our proposal partners and other scientists at neighboring Woods Hole Oceanographic Institution. 

Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.

References:

Pohlman, J.W. Greinert, J., Ruppel, C., Silyakova, A., Vielstadte, L., Casso, M., Mienert, J., Bunz, S., 2017. Enhanced CO2 uptake at a shallow Arctic Ocean seep field overwhelms the positive warming potential of methane. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1618926114.

Pohlman, J.W., Casso, M., Magen, C., Bergeron, E. 2021. Discrete sample introduction module for quantitative and isotopic analysis of methane and other gases by cavity ring-down spectroscopy. Environmental Science and Technology. DOI: 10.1021/acs.est.1c01386.

Proposed Duty Station: Woods Hole, Massachusetts

Areas of PhD: Marine biogeochemistry, microbial ecology, organic geochemistry, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet the qualifications for: Research Chemist 

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact:  Audrey Tsujita, 916-278-9395, atsujita@usgs.gov