Dissolved organic matter (DOM) plays major roles in oceanic and global biogeochemical processes as it is one of the Earth's largest active carbon pools. Determining the detailed composition and structure of DOM offers unparalleled rewards as their informational richness represents a unique set of biogeochemical tracers capable of providing important insights into the origins of their parent waters and the diagenetic alterations that have occurred within those waters during transport. Recent analytical breakthroughs have the potential to bring a major fraction of marine DOM within our analytical window, thus greatly facilitating the reading of DOM's "molecular messages". In addition, there has been promising improvement in the ability to isolate DOM using reverse osmosis coupled with electrodialysis (RO/ED) that can now isolate up to 95% of marine DOM compared to ~10-40% for previous techniques.
In this research, a new investigator from Old Dominion University will lead a team that also includes Georgia Institute of Technology that will combine improved isolation of marine DOM with the unparalleled power of ultra-high resolution FT-ICR MS and advanced NMR spectroscopy to gain major new insights into the composition of marine DOM and the biogeochemical processes controlling its composition. The main goals of this proposed study are to: (1) characterize bio-refractory DOM that dominates the marine DOM pool especially in the deep sea; (2) characterize newly produced DOM in an upwelling region and the semi-biolabile and photobleached DOM that accumulates in oligotrophic, subtropical gyre surface waters; and (3) compare RO/ED isolated DOM to the original sample and to DOM isolated using ultrafiltration and solid-phase extraction (e.g., XAD and C18).
In terms of broader impacts, this research will lay the foundations for future oceanic and global biogeochemical studies where these advanced techniques can be used to trace compounds or component classes of DOM from their multifarious sources, along their various paths of diagenesis and transport, to their points of export, microbial uptake or mineralization. In addition, the PIs will provide critically needed precursory reference material for the marine biogeochemical community. The proposed study will support a new Assistant Research Professor at ODU and three doctoral students. Collaborative ties with investigators from WHOI, MIT and the HOT site will foster cooperative field-based research. Public outreach and information dissemination will be facilitated by creation of a dedicated project website and through public and news media interactions, as appropriate.
Dissolved organic matter (DOM) plays major roles in oceanic and global biogeochemical processes. It accounts for >90% of the organic carbon in the oceans, making it one of the Earth’s largest active carbon pools (~700 Pg C), approximately equal to atmospheric CO2. Consequently, any changes in DOM dynamics can significantly impact the Earth’s carbon-cycle. Despite its importance, the cycling and chemical composition of marine DOM are poorly constrained, with any net shifts largely obscured by analytical limitations. However, recent analytical breakthroughs, especially advanced nuclear magnetic resonance (NMR) spectroscopy involving spectral editing techniques and ultra-high resolution Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) have the potential to bring a major fraction of marine DOM within our analytical window, thus greatly facilitating the reading of DOM’s "molecular messages". Despite the great promise of these techniques, if DOM isolation procedures result in an altered, biased or contaminated sample, then the usefulness of the results will be, at best, limited. The most promising improvement in DOM isolation to date appears to be reverse osmosis coupled with electrodialysis (RO/ED), which we have shown to isolate approximately 75% of marine DOM, compared to ~10-50% for previous techniques. In this project, we combined this major breakthrough in marine DOM isolation (RO/ED) with the unparalleled power of ultra-high resolution FT-ICR MS and advanced NMR spectroscopy, to gain major new insights into the composition of marine DOM and the biogeochemical processes controlling its composition. On two oceanographic cruises, we obtained samples from biogeochemically diverse environments; i.e., photobleached surface gyre, productive coastal upwelled, oxygen minimum, deep Atlantic, and old deep Pacific waters. Through our analyses we were able to: (1) characterize bio-refractory DOM that dominates the marine DOM pool especially in the deep sea; (2) characterize newly produced DOM in an upwelling region; (3) characterize semi-biolabile and photobleached DOM that accumulates in oligotrophic, subtropical gyre surface waters; and (4) compare RO/ED isolated DOM to the original sample and to DOM isolated using solid-phase extraction (i.e., XAD and PPL solid phases) in collaboration with colleagues from the US Geological Survey and the Max Planck Marine Geochemistry Group in Germany. Our results support a 3-pool (labile, semi-labile, and refractory) model of marine DOM. Labile and semi-labile DOM samples were found to be rich in carbohydrate-like material. Evidence of a large pool of ‘background’ refractory carbon was seen throughout the ocean. High carboxyl (i.e., COOH) signals in the deep Pacific support the hypothesis that a major fraction of this refractory pool is carboxyl-rich alicyclic molecules. In addition, advanced NMR spectral editing revealed that condensed aromatic and quaternary anomeric carbons contributed to this deep refractory DOC pool, the quaternary anomeric carbons being an important, but previously unrecognized component of bio-refractory carbohydrates. Our study has helped lay the foundations for future oceanic and global biogeochemical studies where advanced extraction and analytical techniques can be used to trace compounds or component classes of DOM from their multifarious sources, along their various paths of alteration and transport, to their points of export, microbial uptake or mineralization. In addition, we have isolated sufficient amounts of marine DOM to provide critically needed precursory reference material for the marine biogeochemical community. Both US and Canadian collaborators have been funded to carry out further characterization of these samples. Sharing these samples with collaborators in a number of US and international laboratories has fostered collaboration and is offering new insight into the nature of DOM which extends beyond the original proposal goals. The oceanographic cruises with investigators from WHOI, MIT and the HOT-series site (in the Pacific) have fostered cooperative field-based research between these groups and ours, plus exposed the graduate students to state-of-the-art instrumental techniques and the inter-disciplinary and collaborative nature of marine science. The study supported Aron Stubbins, early career scientist and Beginning Investigator who was the initial PI and an Assistant Research Professor at ODU. Due largely to the success of this project Stubbins now holds an Assistant Professor position at the Skidaway Institute of Oceanography. Doctoral students, 3 at ODU and 1 at Georgia Tech, have played critical roles in the project. Two of the ODU students are now in Postdoctoral positions at other institutions. The other two are set to graduate in the near future. To date, the project has directly (and indirectly) produced 13 publications, most of which have appeared in high impact journals. In addition, 16 presentations have been made at national and international meetings and symposiums. Many of these presentations were made by the graduate students supported by the project.
