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My research combines a background in (inorganic) geochemistry with measurements of stable isotopes and an in-depth assessment of microbial activity. I am interested in understanding what modern processes, microbial or chemical, control cycling of nutrients, release of contaminants, and sequestration of carbon. I particularly like to study these processes in low energy environments and across redox transition zones. Much of my work centers around understanding the complex cycling of sulfur and transition metals such as iron and manganese, however, I do have a few current projects outside of this sphere.

Below I will mention some projects I am working on or have worked on in the past.  


Glass microelectrode profiling a sediment core with eelgrass


Much of my research takes advantage of the high spatial and temporal measurement of dissolved species I am able to obtain using my specialized, hand-crafted Au/Hg microelectrodes. These microelectrodes can simultaneously detect dissolved oxygen, sulfide, thiols, iron, manganese, thiosulfate, iron sulfide, and organic-Fe(III) among other compounds. I have used these microelectrodes to get high resolution depth profiles of compounds in sediment cores from numerous marine and freshwater locations. I have used the ability to obtain high temporal resolution to aid in understand the molecular mechanism in abiotic reactions.  Due to the non-destructive and minimally invasive nature of these electrodes they are excellent for monitoring microbial incubations as well. Recently I have used these microelectrodes to investigate the rhizosphere of seagrass. 

Carbon Dioxide Removal

Increasing carbon dioxide in the atmosphere contributes to global warming and ocean acidification. Numerous carbon dioxide removal (CDR) techniques will be required to reach the climate change mitigation goals set by the international community and outlined in the Paris Agreement. My experience working on enhanced weathering of silicate minerals in blue carbon environments has given me insight into CDR approaches and an understanding of the challenges that large scale carbon dioxide sequestration will face.


Herring River, Cape Cod, MA


Sulfur Cycling

When sulfate is limiting, do microbes respire on other inorganic sulfur species? Could these processes be more favorable than classic sulfate reduction? How are sulfur redox intermediates linked to other processes, such as the anaerobic oxidation of methane? These are some of the questions I am investigating in cold methane seep sediments using stable isotopes and 'omics. 


Cold methane seep as seen in the ROV Doc Ricketts control room


ROV Doc Ricketts


Mono Lake, CA


Sediment coring with Larry Miller (USGS)

Anthropogenic Impact

Mono Lake, an alkaline, closed basin lake in California, experienced a nearly 45 ft water level drop over a 40-year period beginning in 1941 due to diversion of freshwater tributaries. Sediment in this lake has distinct lamination, excellent preservation of DNA, and extreme sulfur isotope fractionation. Understanding the biogeochemical sulfur cycle in this unique environment may help us understand how anthropogenic activities are preserved in relatively modern records.

Wildfire Recovery

Wildfires can rapidly release huge amounts of carbon into the atmosphere and completely change entire ecosystems. Understanding how the rhizosphere recovers after wildfires, especially in areas which are projected to burn more frequently is extremely important. To study the microbial and geochemical response to wildfire, I conducted a 2 year study comparing burned and unburned soil in the San Gabriel mountains, CA following a wildfire. 


Burn scar, San Gabriel mountains


In situ incubations, Mono Lake


NanoSIMS showing 15N uptake by a Picocystis cell

Nitrogen Cycling

In addition to having a unique sedimentary record, Mono Lake is an important feeding ground for many migrating birds. The lake food chain revolves around the primary producer, Picocystis, a high salinity adapted micro-algae which contributes to the green color of the lake.  With the International Geobiology Course I have become interested in how these key species are surviving in nitrogen limited conditions and why they might be transcribing photosynthesis genes deep in the lake where light is absent. 

Contaminant Transformation

Determining the dominant biogeochemical processes occurring in an environment is foundational to understanding how contaminants are retained, released, or transformed. Combining microelectrode measurements and 'omics is helping us understand the competitive anaerobic redox dynamics which control the fate of Hg and U in two contaminated sites in Tennessee and South Carolina.






Port window, Rhone River Delta, RV Tethys II

Benthic Alkalinity Production

Although coastal regions are generally considered a net source of atmospheric carbon dioxide due to high organic carbon remineralization, increased anaerobic respiration processes combined with burial of reduced chemical species can result in net alkalinity production. Understanding the processes which contribute to alkalinity consumption vs. production is particularly important in deltaic regions that receive large seasonal deposition of organic and inorganic matter. In the Rhone River Delta we determined that burial of iron sulfide minerals in the spring and summer may leads to increased alkalinity release to bottom waters, potentially allowing these regions to act as a carbon sink.

(Rassmann and Eitel et al., 2020)

Marine Iron Cycling

Iron is a limiting nutrient in most of the ocean and benthic release of iron in passive continental margins is often considered negligible, especially in areas with no major riverine input or upwelling. However, high resolution profiles of dissolved iron measured along a transect off the coast of North Carolina demonstrates that mid-slope depocenters contribute considerably to the bioavailable iron inventory of the ocean. 

(Eitel et al., 2020)


Multi-core collection off the coast of NC

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