Martens Lab Research
Microbiology of Anaerobic Methane Oxidation (Teske and Martens labs)
The microbiology of anaerobic methane oxidation in hydrothermal and cold marine sediments constitutes a shared interest of the Teske and Martens labs, and has led to collaborative ties and joint proposals. A focus site of the Teske lab is the Guaymas Basin, a sedimented hydrothermal vent site in the Gulf of California. Here, thermal degradation of sedimentary organic matter produces thermogenic methane that supports anaerobic methane-oxidizing communities. The first occurrence of anaerobic methane oxidation in hydrothermal environments was found by the Teske group at Guaymas. A newly-submitted NSF proposal (Teske, Martens, Albert & MacGregor) focuses on a joint geochemical and microbiological analysis of this vent system. Graduate students Karen Lloyd (Teske lab) and Laura Lapham (Martens lab) are working on a combined geochemical and biological analysis of a methane-rich sediment community in the Gulf of Mexico.
Community Analyses of Deep-Subsurface Sediments
The sediment cover of the ocean bottom is usually several 100 meters thick and permeated by microbial life top to bottom. This is perhaps the most extensive and least explored microbial habitat on Earth. The structure and metabolic activities of these deep subsurface communities are a current research challenge. The Teske Lab is analyzing the microbial community composition in a range of geochemically divergent subsurface sediments (Nankai Trough; Peru Margin and Equatorial Pacific; Juan de Fuca Ridge flank). This project involved two recent postdocs (Ketil Sørensen and Antje Lauer), and graduate students Mark Lever and Karen Lloyd.
Deep subsurface projects also include a recently-submitted joint NSF proposal with the Noble lab that aims at the detection and DNA/RNA analysis of subsurface viruses. Since 2000, the Teske lab has been working with the Ocean Drilling Program and its successor, the International Ocean Drilling Program (IODP). On recent ODP and IODP cruises targeting the deep subsurface biosphere, members of the Teske lab sailed on JOIDES Resolution (Figures 3.3a and 3.3b), the deep-sea drilling vessel for retrieving otherwise inaccessible deep subsurface samples. Much of this work is carried out with colleagues at the Univ. Rhode Island and with the Marine Biological Laboratory (Woods Hole, MA).
Martens’ group research focuses primarily on key processes controlling the biogeochemical cycling of carbon and nitrogen in organic-rich marine and tropical ecosystems. The work includes combined studies of microbial transformations and physical transport processes at well-characterized field sites including tropical forest, wetland, estuarine, nearshore and deep-sea environments. Emphasis is placed on investigating exchange processes and net chemical fluxes between sediments, water column and atmospheric reservoirs.
Amazonian tropical forests as CO2 and trace gas sources and sinks
The need to understand the role of the Amazon and other tropical forests as globally significant CO2 sinks and potential sources or sinks for other radiatively important trace gases such as CH4 and N2O, resulted in a major international research program led by Brazil, the Large-scale Biosphere Atmosphere (LBA) Program. The program includes an emphasis on the impact of land-use change on CO2 and trace gases fluxes. Initial gas flux measurements yielding net CO2 uptake relied entirely on one-dimensional eddy covariance measurements until the Martens group developed an independent method for quantifying forest canopy-atmosphere gas exchange rates over long time-periods (months to years) using continuous measurements of in- and above-canopy radon-222 activity in combination with determination of the radon flux from underlying soils. We have invented, designed and built a new generation of pulsed ionization continuous radon analyzers at UNC that have functioned in Brazil year-round since April 2000. Using these analyzers, we have been able to demonstrate that the eddy covariance methods were unable to accurately measure nighttime CO2 losses (Martens et al., 2003), thus producing the net CO2 sink result. Our data are also proving useful for investigating soil gas release processes and fluxes in Brazilian Amazonia. Our radon array systems are also now in use at one of the DOE-funded FACE (Free Air CO2 Exchange) sites in Duke Forest and at several other sites along the NC coast where we are experimenting with tracing continental-maritime air exchange processes.
The role of marine sponges in the C and N cycles of coral reef and nearshore waters.
Our NSF and NURC projects are directed at understanding the role of marine sponges in the carbon and nitrogen cycles of coral reef ecosystems. Sponges are an important part of these endangered ecosystems, yet little is known about their role in the transformations and cycling of key nutrient elements, particularly nitrogen.
The stable C isotopic composition of sponges along natural environmental gradients in the Florida Keys exhibit significant spatial gradients related to organic carbon sources whereas N isotopes divide sponges into two distinct groups. Sponges hosting large populations of bacteria are more hypoxic, pump less water and have excurrent waters enriched in nitrate rather than ammonium, signaling microbial nitrification. Hypoxic conditions in bacteriosponges provide potential for other N transformations including N2 fixation and denitrification. The potential impacts of these processes on the overall nutrient budget of the reef system are large; we are developing collaborative experiments with a fluid dynamics group at Stanford in order to obtain quantitative N flux results. Collaborators include UNC Ph.D. students, Niels Lindquist, Dr. Brian Popp and Jan Riechelderfer (U. Hawaii), and Prof. Dr. Ute Henschel and Dr. Susanne Schmidt (Univ. Würzburg, Germany).
Biogeochemical processes controlling formation and decomposition of methane hydrates
Our NOAA funded research on methane hydrates is focused on novel submersible and ROV deployed probes combined with in situ biogeochemical rate measurements to investigate biogeochemical processes controlling their formation and decomposition in Gulf of Mexico margin sediments. The biogeochemical processes data is combined with geophysical data in order to quantify the extent and nature of in situ processes controlling the formation and decomposition of exposed and buried gas hydrate deposits.
We have successfully deployed methane pore water probes from submersibles and ROVs obtaining the world’s first un-decompressed methane gas samples for both chemical and stable isotopic analysis. The results provide information about both methane gas sources and microbial transformations including methane consumption via anaerobic methane oxidation, a process first hypothesized in 1974 (Martens and Berner, Science). Work on methane fluxes from sediments at hydrate sites will include continuous remote water column and seafloor measurements with a team of Woods Hole scientists led by Jean Whelan and Rich Camilli, using novel in situ mass spectrometer and chemical sensors in the Gulf at approximately 850m depth (See Figure 3.6).
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