Collaborative Research: Microbial Biomarkers at the Chemocline of the Cariaco Basin: Linking Organic Geochemistry and Microbial Ecology

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In this project, researchers at the Skidaway Institute of Oceanography and the Pennsylvania State University will investigate the relationship between biomarker distributions and microbial processes at the chemocline of the Cariaco Basin, Venezuela. The overriding hypothesis is that chemoautotrophy within the chemocline produces a set of biomarkers with diagnostic isotopic compositions that, when deposited in underlying sediments, provides a record of water column chemoautotrophic carbon production and sedimentation in the Cariaco Basin. The fidelity of sedimentary biomarkers as indicators of water column microbial processes depends upon linking biomarkers with their microbial sources. The project has three specific objectives: 1) To obtain depth profiles of microbial biomarkers and microbial community structure through closely spaced sampling at the chemocline of the Cariaco Basin, and thereby evaluate lipid biomarker-source relationships. The investigators will also measure biomarkers in sediment trap samples and surface sediments to determine how well sediments record water column chemoautotrophy. 2) To apply state-of-the-art analytical techniques for biomarker analyses, notably high performance liquid chromatography/electrospray ionization ion trap multistage mass spectrometry (HPLC/ESI-IT-MSn) to analyze intact bacterial and archaeal biomarkers. The investigators contend that the biomarker potential of intact polar lipids (IPLs) is significantly greater than that obtained by traditional hydrolysis based analyses. 3) To fully exploit the biogeochemical information inherent in lipid biomarkers by linking biomarkers with their biological sources and the processes by which they are produced. Spatial and temporal patterns in molecular and microbial signatures will form the foundation for understanding these linkages, which will be strengthened by companion measurements of the 13C content of lipids and key carbon substrates (methane, inorganic carbon, and if available, acetate). This cross-disciplinary project has a number of broader impacts. Most of the biomarker work will be carried out by Skidaway Institute of Oceanography, but the project is a collaborative effort between investigators having expertise in diverse disciplines and representing several laboratories in the US, Europe, and Venezuela. At Skidaway, a postdoctoral investigator will focus on the organic geochemical component and will work closely with the various organic geochemical partners (NIOZ, Bremen). Venezuelan scientists will participate on cruises in order to provide additional interaction and training.