Keynote Abstracts
Pedro Verdugo
Marine Biopolymer Dynamics
DOM comprises one of the largest stocks of reduced organic Carbon present in our planet reaching ~700 Gt. However, the fate of these molecules, their chemical, physical, and biological interactions and their ultimate destination remain as one of the most intriguing and significant challenges in geochemistry and marine biology. DOM lies at the bottom of the food chain as it comprise the basic fuel for marine microorganisms. One of the most significant features of DOM is that these polymers can self-assemble remaining in reversible equilibrium forming microscopic gels. In the laboratory DOM self-assembly has a thermodynamic yield of ~10% generating a corresponding estimated pool that could reach ~70 Gt (Nature 391:568-572, 1998). Microscopic gels similar to those assembled in the laboratory are present in the water column from surface down to 4000 meters deep at concentrations ranging from 106 to 1012 microgels´L-1 reaching a corresponding estimated global mass of ~ 1-100 Gt (Mar Chem 106: 229-239, 2007; Faraday Discuss. RSC 139: 393-398, 2008). Compared to bulk seawater these gels contain an estimated one thousand step increase of organic matter concentration that remains available as a rich nutrient source for bacterial mineralization. Marine biopolymers exhibit a complex dynamics that results from multiple interactions of chemical, physical and biological processes that still remains poorly understood. Understanding this process is most critical to model carbon cycling and to develop reliable predictions about the equilibrium and distribution of organic and inorganic moieties in seawater and their effects on marine biota.
Paula Coble
Fluorescence of Coastal and Marine Waters
The natural fluorescence of organic matter was first reported for seawater well over fifty years ago using direct microscope observations. It has also long been recognized that the source of this material is both from terrestrial runoff and from in situ formation related to biological productivity and perhaps chemical browning reactions. Two main types of fluorescence have been observed in all aqueous systems – humic-like and amino acid-like.
The early studies were focused on two main scientific pursuits: use of CDOM as a natural tracer of mixing of water masses in coastal areas, and investigation of the optical transparency of ocean waters, a field which was to develop into Optical Oceanography. This paper will provide a brief review of what is known about distribution, sources, and cycling of fluorescent CDOM in coastal and open ocean waters and highlight some more recent applications of fluorescence spectroscopy in the study of carbon cycling in the ocean.
Colin Stedmon
Tracing the distribution and turnover of organic matter from land to sea using fluorescence and absorption spectroscopy.
The optical characteristics of coloured dissolved organic matter (CDOM) provide an effective way of tracing and characterising dissolved organic matter in aquatic environments. Absorption measurements allow us to distinguish between different pools of organic matter, and also quantify CDOMs effect on light penetration and water colour. The former being central to primary productivity in aquatic environments and the latter essential for the use of satellite based ocean colour remote sensing. Fluorescence measurements are much more sensitive and are revealing the complexity of DOM as a mixture of components. Despite this complexity, clear trends can be found in the fluorescence signal. In this talk I will briefly discuss the role that microbes and abiotic process may play in producing CDOM. Next a couple of examples will be shown. The first will be from the Arctic Ocean where absorption measurements can be used to follow and quantify the input of terrestrial material into the surface waters. The differing spectral properties between, riverine, oceanic and recently produced marine CDOM not only provide and indicator of the relative importance of the different sources but also insight on the origins of different water masses. The second example will be from a unique global oceanic data set of DOM fluorescence measurements. Here trends reveal that the distribution of different sub-fractions of DOM are controlled by mixing, photochemical removal and microbial production.
Diane McKnight
Reactivity of humic substances in aquatic ecosystems as revealed by fluorescence spectroscopy
Humic substances are an important class of reactive chemical species in natural waters, and one important role is their capacity to as an electron acceptor and/or electron shuttle to ferric iron present as solid phase ferric oxides. Several lines of evidence point to quinone-like moieties being the main redox active moieties that can be used by microbes in respiration. Concomitantly, the humic fraction of dissolved organic mater (DOM) contains the dominant fluorophores in many natural waters, such that the commonly occurring Peak C is referred to as the “humic” peak. Furthermore, there is striking similarity between the humic fluorophores that are resolved by statistical analysis, specifically PARAFAC, and the fluorescence spectra of model quinone compounds, with the more reduced species having red-shifted fluorescence spectra. Examination of excitation emission matrices (EEMs) across redox gradients in diverse aquatic systems show that the EEMs are also red-shifted under reducing conditions, such as anoxic bottom waters in lakes and hypoxic waters in riparian wetlands. This apparent red-shift can be quantified based on the distribution of apparently oxidized quinone-like and more reduced, semi-quinone-like and hydroquinone-like fluorophores determined by PARAFAC. Because fluorescence spectroscopy can be applied at ambient DOM concentrations for samples that have been maintained in an anoxic condition, fluorescence spectroscopy can potentially provide insight into complex problems in environmental biogeochemistry, such as the role of organic material in the mobilization of arsenic in shallow groundwater in South East Asia.
Marine Biopolymer Dynamics
DOM comprises one of the largest stocks of reduced organic Carbon present in our planet reaching ~700 Gt. However, the fate of these molecules, their chemical, physical, and biological interactions and their ultimate destination remain as one of the most intriguing and significant challenges in geochemistry and marine biology. DOM lies at the bottom of the food chain as it comprise the basic fuel for marine microorganisms. One of the most significant features of DOM is that these polymers can self-assemble remaining in reversible equilibrium forming microscopic gels. In the laboratory DOM self-assembly has a thermodynamic yield of ~10% generating a corresponding estimated pool that could reach ~70 Gt (Nature 391:568-572, 1998). Microscopic gels similar to those assembled in the laboratory are present in the water column from surface down to 4000 meters deep at concentrations ranging from 106 to 1012 microgels´L-1 reaching a corresponding estimated global mass of ~ 1-100 Gt (Mar Chem 106: 229-239, 2007; Faraday Discuss. RSC 139: 393-398, 2008). Compared to bulk seawater these gels contain an estimated one thousand step increase of organic matter concentration that remains available as a rich nutrient source for bacterial mineralization. Marine biopolymers exhibit a complex dynamics that results from multiple interactions of chemical, physical and biological processes that still remains poorly understood. Understanding this process is most critical to model carbon cycling and to develop reliable predictions about the equilibrium and distribution of organic and inorganic moieties in seawater and their effects on marine biota.
Paula Coble
Fluorescence of Coastal and Marine Waters
The natural fluorescence of organic matter was first reported for seawater well over fifty years ago using direct microscope observations. It has also long been recognized that the source of this material is both from terrestrial runoff and from in situ formation related to biological productivity and perhaps chemical browning reactions. Two main types of fluorescence have been observed in all aqueous systems – humic-like and amino acid-like.
The early studies were focused on two main scientific pursuits: use of CDOM as a natural tracer of mixing of water masses in coastal areas, and investigation of the optical transparency of ocean waters, a field which was to develop into Optical Oceanography. This paper will provide a brief review of what is known about distribution, sources, and cycling of fluorescent CDOM in coastal and open ocean waters and highlight some more recent applications of fluorescence spectroscopy in the study of carbon cycling in the ocean.
Colin Stedmon
Tracing the distribution and turnover of organic matter from land to sea using fluorescence and absorption spectroscopy.
The optical characteristics of coloured dissolved organic matter (CDOM) provide an effective way of tracing and characterising dissolved organic matter in aquatic environments. Absorption measurements allow us to distinguish between different pools of organic matter, and also quantify CDOMs effect on light penetration and water colour. The former being central to primary productivity in aquatic environments and the latter essential for the use of satellite based ocean colour remote sensing. Fluorescence measurements are much more sensitive and are revealing the complexity of DOM as a mixture of components. Despite this complexity, clear trends can be found in the fluorescence signal. In this talk I will briefly discuss the role that microbes and abiotic process may play in producing CDOM. Next a couple of examples will be shown. The first will be from the Arctic Ocean where absorption measurements can be used to follow and quantify the input of terrestrial material into the surface waters. The differing spectral properties between, riverine, oceanic and recently produced marine CDOM not only provide and indicator of the relative importance of the different sources but also insight on the origins of different water masses. The second example will be from a unique global oceanic data set of DOM fluorescence measurements. Here trends reveal that the distribution of different sub-fractions of DOM are controlled by mixing, photochemical removal and microbial production.
Diane McKnight
Reactivity of humic substances in aquatic ecosystems as revealed by fluorescence spectroscopy
Humic substances are an important class of reactive chemical species in natural waters, and one important role is their capacity to as an electron acceptor and/or electron shuttle to ferric iron present as solid phase ferric oxides. Several lines of evidence point to quinone-like moieties being the main redox active moieties that can be used by microbes in respiration. Concomitantly, the humic fraction of dissolved organic mater (DOM) contains the dominant fluorophores in many natural waters, such that the commonly occurring Peak C is referred to as the “humic” peak. Furthermore, there is striking similarity between the humic fluorophores that are resolved by statistical analysis, specifically PARAFAC, and the fluorescence spectra of model quinone compounds, with the more reduced species having red-shifted fluorescence spectra. Examination of excitation emission matrices (EEMs) across redox gradients in diverse aquatic systems show that the EEMs are also red-shifted under reducing conditions, such as anoxic bottom waters in lakes and hypoxic waters in riparian wetlands. This apparent red-shift can be quantified based on the distribution of apparently oxidized quinone-like and more reduced, semi-quinone-like and hydroquinone-like fluorophores determined by PARAFAC. Because fluorescence spectroscopy can be applied at ambient DOM concentrations for samples that have been maintained in an anoxic condition, fluorescence spectroscopy can potentially provide insight into complex problems in environmental biogeochemistry, such as the role of organic material in the mobilization of arsenic in shallow groundwater in South East Asia.