Dissolved organic matter (DOM) contains as much carbon as all living biomass on the continents and oceans combined and plays a major role in global biogeochemical cycles. As bacteria can assimilate and respire only dissolved molecules, DOM represents the main mediator of energy flux in marine and freshwater ecosystems. While most of the molecules released by phytoplankton at the surface are respired in seconds to decades, a fraction of DOM escapes remineralization and can persist in the ocean for millennia. As these molecules carry the signatures of their source and subsequent journey through the marine environment, they parallel the sedimentary record as an information-rich set of tracers. Moreover, the molecular diversity of the marine DOM pool poses a metabolic challenge to microbial communities that rely on its utilization. Using interdisciplinary approaches to couple global scale analyses of DOM with microbial and molecular level research is important to fully understand this important pool of carbon. For this session, we invite contributions from all areas of research on DOM biogeochemistry, including both empirical and modeling studies. We encourage contributions that apply innovative analytical approaches, or identify novel concepts, fundamental challenges and the future directions of this fast growing field of research.
Lead Organizer: Sinikka Lennartz, University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment (sinikka.lennartz@uni-oldenburg.de)
Co-organizers:
Sarah Bercovici, University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment, Germany (sarah.bercovici@uni-oldenburg.de)
Jessika Fuessel, University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment, Germany (jessika.fuessel@uni-oldenburg.de)
Brett Walker, University of Ottawa, Department of Earth and Environmental Sciences, Canada (bwalker3@uottawa.ca)
Taichi Yokokawa, Agency for Marine-Earth Science and Technology, Japan (taichiyokokawa@gmail.com)
Presentations
08:30 AM
From Molecules to Ecosystem Function - A Metabolomics View on Dissolved Organic Matter (5189)
Tutorial/Invited: Invited
Primary Presenter: Daniel Petras, University of Tuebingen (functionalmetabolomics@gmail.com)
The chemical composition of the ocean’s community metabolome represents a fascinating source of chemical entities that are fundamentally important for ecosystem function and planetary processes such as global carbon cycling. Thanks to recent advances in tandem mass spectrometry and computational data analysis tools, we can identify a wide range of metabolites out of this ultra-complex mixture and propose some of their activities through literature knowledge. However, the number of known metabolites and activities represents only a small fraction of all compounds we can detect in these environments. To fully map out the structural and bioactivity space, new methods are needed, as traditional isolation and bioactivity studies do not scale to contemporary non-targeted metabolomics workflows. To address this need, we develop functional metabolomics tools that integrate multi-dimensional liquid chromatography tandem mass spectrometry with bioactivity profiling as well as native mass spectrometry. In combination with molecular networking, these workflows allow us to screen complex environmental samples for bioactivity, metal and protein binding and metabolic transformations. Taken together, our results provide new insights in the enormous chemical complexity of DOM and highlight the potential of functional metabolomics workflows for the linking of environmental metabolomics data and bioactivity, which we hope will contribute to a systematic mapping of the functional role and fate of small molecules in complex environmental systems.
08:45 AM
NEW INSIGHTS ON DISSOLVED ORGANIC MATTER CYCLING IN THE CAPE VERDE FRONTAL ZONE (CVFZ) FROM ITS OPTICALLY ACTIVE FRACTION (4891)
Primary Presenter: Xosé Antón Alvarez-Salgado, CSIC Instituto de Investigacións Mariñas (xsalgado@iim.csic.es)
The CVFZ is a highly dynamic ocean margin characterised by two well-defined oceanographic features: the thermohaline Cape Verde Front (CVF), that separates the subtropical from the tropical waters of the Northeast Atlantic, and the Cape Blanc Giant Filament (CBGF), which exports the organic matter produced in the Mauritanian upwelling to the open ocean. During an oceanographic cruise in the summer of 2017, we sampled a hydrographic box encompassing the CVFZ. Full-depth profiles of absorption spectra of coloured (CDOM) and excitation-emission matrices of fluorescent (FDOM) dissolved organic matter were collected and examined to produce an assortment of CDOM indices and 5-FDOM PARAFAC components. In epipelagic waters, we identified distinctive optical signatures in open ocean waters north and south of the CVF and in coastal waters transported by the CBGF that provide new insights on the origin (terrestrial vs. marine), photochemical and microbial reactivity (lability vs. recalcitrance), and molecular properties (molecular weight, aromaticity) of dissolved organic matter (DOM). In mesopelagic waters, we optically characterised the water masses of opposing origin that meet in the CVFZ: North and South Atlantic Central Water, Subpolar Mode Water, Mediterranean Water, Antarctic Intermediate Water and Labrador Seawater. In bathypelagic waters, we recognised the bottom nepheloid layer close to the Mauritanian coast as a massive source of optically active DOM that is not noticeable in dissolved organic carbon (DOC) distibutions.
09:00 AM
Rivers and porewater outwelling as sources of dissolved organic matter and trace metals in the German Bight (North Sea) (5949)
Primary Presenter: Michael Seidel, University of Oldenburg (m.seidel@uni-oldenburg.de)
The German Bight (southern North Sea) receives nutrients, dissolved organic matter (DOM), and trace metals via rivers and tide-driven submarine groundwater discharge (SGD). However, deciphering DOM sources and transformations in highly dynamic coastal settings remains challenging. We present a study assessing the different marine, riverine, and porewater (sulfidic) sources and characterizing molecular transformations of solid-phase extracted (SPE) DOM in the German North Sea using ultrahigh-resolution mass spectrometry (FT-ICR-MS), in combination with quantitative dissolved organic sulfur (DOS), and dissolved black carbon (DBC), as well as with dissolved trace metal (Ba, Co, Fe, Gd, Mo, Mn, W), and dissolved nutrient (nitrite, nitrate, phosphate, silicate) data. Despite the importance of rivers, porewater outwelling was a major source for dissolved nutrients, and several trace metals as well as potentially recalcitrant DOM (DOS) to the southern North Sea. Riverine DOS was amended by (sulfidic) porewater discharge as revealed by non-conservative behavior of elemental carbon-to-sulfur ratios and sulfur-content of molecular formulae (from FT-ICR-MS). Discharging oxygen-depleted porewater was a source for dissolved phosphate, whereas dissolved Mn and Si were removed in the German Bight which was probably due to precipitation as Mn(hydr)oxides and biological uptake, respectively. We show that porewater discharge must be considered in addition to riverine sources to understand the complex interplay of DOM, nutrient, and trace metal transformations in coastal ecosystems.
09:15 AM
Internal sulfur cycling drives sulfurization of organic matter in Florida Bay sediments (5120)
Primary Presenter: Mary Zeller, University of Bremen (maryazeller@gmail.com)
Dissolved organic sulfur is known to be produced in areas with abundant sulfide and abundant organic matter, however less is known about its production in oligotrophic carbonate systems with relatively low organic matter content, as dominates the coastal tropics and subtropics. Here, we explore a seagrass meadow in central Florida Bay. Using a combination of stable isotopes (C, S, O) and Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS), we reveal the connections between vegetation, sulfurization of carbonate-associated organic matter, and its release to the water column. We find that seagrass mediated oxygen pumping in the rhizosphere fuels sulfide oxidation, which determines the low net rates of sulfate reduction observed despite high gross rates. This sulfide oxidation in turn contributes to localized carbonate dissolution, while carbonate precipitation elsewhere leads to low net rates of precipitation. FT-ICR-MS analysis reveals intense sulfurization of carbonate-associated “dissolvable” organic matter likely through a combination of reactions with sulfide, polysulfides, and other sulfur intermediates, while the rapid cycling of carbonate dissolution and precipitation allows for the connectivity of this pool with the porewater and water column. Despite low net rates of sulfate reduction and carbonate dissolution, this system is a factory for the sulfurization of already highly photodegraded and likely recalcitrant, dissolved organic sulfur.
09:30 AM
Cryptic cycling of high molecular weight dissolved organic matter in the hypolimnion of a deep lake (5026)
Primary Presenter: Yasuhiko Yamaguchi, Lake Biwa Environmental Research Institute (yamaguchi-y@lberi.jp)
The hypolimnion of deep lakes is the site where essential ecosystem functions such as O2 consumption and nutrient regeneration occur. We conducted long-term biodegradation experiments and field surveys on a large, deep lake (Lake Biwa, Japan) to elucidate the dynamics of dissolved organic matter (DOM) in the hypolimnion. The biodegradation experiments (>250 days) were conducted with hypolimnetic water collected in March 2020 (the mixing period). The water samples were incubated in the dark at 9°C (the water temperature of the hypolimnion) or 20°C. The hypolimnetic waters at the same site were collected monthly from March to December 2020 (through the stratified period). The molecular size distribution of DOM was quantified using a size-exclusion chromatograph coupled with a total organic carbon detector (SEC-TOC). The net degradation rates of high molecular weight DOM (HMWDOM: Mw ~ 100kDa) were estimated for each concentration time series. The rates were faster in the order of the 20°C experiment > the 9°C experiment > and the monthly time series of hypolimnetic waters. This result indicates that the HMWDOM production fueled by sinking particles would be considered to explain the apparent persistence of HMWDOM in the hypolimnion. We also estimated the gross degradation flux (= the net degradation flux + the production flux) of HMWDOM in the hypolimnion, which was 4 times higher than the net degradation flux. The cryptic cycling of HMWDOM was linked to O2 consumption in the hypolimnion, suggesting that it should be a critical biogeochemical process in deep lakes.
09:45 AM
Dissolved organic matter concentrations and transformations in the water masses of the Brazil-Malvinas Confluence (5371)
Primary Presenter: Pol Rojas, Universitat de Barcelona, Barcelona, Spain (polrojas@ub.edu)
Dissolved organic matter (DOM) is an important component of the global carbon cycle. However, achieving sufficient knowledge of its global distribution, particularly in the ocean, remains a challenge. The Brazil-Malvinas Confluence (BMC) is of particular interest to this respect, as subantarctic and subtropical waters of very different characteristics meet in the BMC. Further, the BMC is an important site for the returning Atlantic Meridional Overturning Circulation (AMOC), largely setting the latitudinal rate of transfer of key properties. Dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) tend to accumulate, especially in the upper waters, becoming a significant component of the return of carbon and nutrients and influencing the nutrient balance of the North Atlantic. Therefore, a good knowledge of the distribution of DOC, DON and DOP in the BMC region is very relevant. Here, we report hydrographic data and DOC, DON and DOP concentrations obtained from two cruises across the BMC. We found, in the upper 1000 m of the region, a range of 36-125 µmol·kg-1 DOC, 0.2-26 µmol·kg-1 DON and 0.1-2 µmol·kg-1 DOP. We performed an inverse optimum multi-parameter (OMP) analysis with the aim of estimating the changes in the dissolved organic carbon and nutrient concentrations of the different water types, hence providing a better context for studying the distribution and transformation of DOM along the BMC system.
SS089A The Biogeochemistry of Dissolved Organic Matter
Description
Time: 8:30 AM
Date: 5/6/2023
Room: Sala Palma