The route from fixation of carbon by photosynthesis in the euphotic zone to its ultimate burial in bottom sediments or remineralization at depth is extremely complex and circuitous, involving biotic and abiotic processes acting differently on various compound classes and particle size fractions. A critical step in the pathway from fixation to burial / sequestration is the remineralization of small particulate organic matter (POM) and colloidal / dissolved organic matter (C/DOM) by the microbial loop, a group of microorganisms including bacteria and protozoan grazers. This group of microbes plays an integral role in the remineralization and modification of organic carbon compounds in all areas of the ocean, from coastal eutrophic areas to open-ocean oligotrophic regimes. Though this role of the microbial web in OM cycling in the coastal and open ocean has been well-established, molecular-level understanding of the transformations within different pools of organic matter (OM) has not been possible due to analytical limitations.
In this study, a researcher at Barnard College will examine these transformations using isotope-ratio gas chromatography/ mass spectrometry (irGC/MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Laboratory cultures of protozoa, bacteria and/or phytoplankton will be monitored for changes in OM composition as a function of time. The prey cultures will be isotopically-labeled with either C13-acetate (bacterial prey) or C13-bicarbonate (phytoplankton prey). Incorporation of the C13-label from prey material will be tracked through the protozoan digestive process and the lability of different OM fractions within grazing cultures can be estimated. Laboratory results will be extended to the field with incubations of size-fractionated seawater from coastal (NY) and oligotrophic (Bermuda) environments. By monitoring OM components on a molecular level, this study has an unprecedented opportunity to elucidate mechanisms for carbon preservation in the marine environment.
This CAREER award will strengthen interdisciplinary training for undergraduate students at Barnard College and increase the number of young female scientists who enter the environmental science pipeline and continue on to graduate school in environmental chemistry.
