Organic matter in aquatic environments includes dissolved and particulate compounds with varying lability, ranging from labile compounds that turn over rapidly, such as amino acids and carbohydrates, to refractory components that persist for thousands to millions of years. The lability of organic matter influences its fate, either incorporation into microbial biomass, respiration by heterotrophic microbes, or export to various regions. Organic matter lability is influenced by intrinsic molecular properties, as well as biotic factors, such as microbial abundance, enzymes, and community composition. In addition, abiotic factors, such as photochemical reactions, oxygen stress, sorption/desorption, and physical aggregation/disintegration, also influence the transformation and fate of organic matter. While recent advances in chemical analysis and microbial studies have significantly enhanced our understanding of these processes, several big questions remain regarding the fate of organic matter. When and where do biotic versus abiotic factors dominate organic matter transformations? Can we identify common principles that determine the fate of organic matter across all water bodies? In this session, we invite presentations on the lability and fate of organic matter in aquatic environments, including but not limited to chemical characterization, ecosystem-specific studies on organic matter source and fate, microbial production and uptake, and pathways of degradation and transformation. We welcome both field observation and lab experimental studies, aiming to synthesize research across disciplines and better understand the factors shaping organic matter lability and its role in biogeochemical processes in aquatic environments.
Lead Organizer: Shuting Liu, Kean University (liushut@kean.edu)
Co-organizers:
Yuan Shen, Xiamen University (yuanshen@xmu.edu.cn)
John Paul Balmonte, Lehigh University (jpb422@lehigh.edu)
Presentations
09:00 AM
New Antimicrobial and Refractory Dissolved Organic Matter Tracers in the Deep Ocean (8846)
Tutorial/Invited: Invited, Tutorial
Primary Presenter: Michael Gonsior, University of Maryland Center for Environmental Science (gonsior@umces.edu)
Dissolved organic matter (DOM) in the deep ocean is considered to be refractory. However, the term refractory DOM (RDOM) is somewhat arbitrary, especially when we divorce radiocarbon measurements from residence time. Evidence is growing that the 2-endmember mixing as the bases of radiocarbon age determination is failing due to additional 14C-free sources of organic carbon entering the interior of the oceans. Hence, we need alternative tracers for DOC residence time and turnover to better predict residence time. Determination of specific structures of deep ocean DOM and within the RDOM pool has been very slow and we are still lacking any true tracers that originate from in situ processes which accumulate in the deep ocean. Developments in mass spectrometry interfaced with liquid chromatography have advanced the field, but the presumed extremely low concentrations of individual compounds in complex DOM mixtures have restricted progress. Here I show that the utilization of the most sensitive and not high-resolution MS approaches is able to assist in structural elucidation. New structures will be presented that contain nitrogen and have antimicrobial properties. A newly developed quantification method of these intriguing new tracers for deep ocean DOM will also be presented.
09:30 AM
Experimentally capturing microbial drivers of POM chemical transformations at BATS (9362)
Primary Presenter: Jacqueline Comstock, UC Santa Barbara (jcomstock@ucsb.edu)
The sinking of particulate organic matter (POM) acts as the primary pathway of the biological carbon pump. However, only a fraction of POM that exits the upper euphotic reaches the base of the mesopelagic due to a variety of food web processes that remineralize, transform, and solubilize particles. Systematic changes in POM isotopic and carbohydrate composition, as well as particle-associated prokaryotes, have been resolved over depth at the Bermuda Atlantic Time-series Study site (BATS). However, both photosynthetic and heterotrophic processes can affect POM composition, making it difficult to differentiate factors driving transformation over depth. Here we aimed to experimentally capture the transformation of naturally occurring POM under heterotrophic control in the euphotic and upper twilight zone to better constrain the relative role microbes play in POM transformation. We collected naturally occurring POM and resuspended it in unfiltered water from depths in the euphotic and twilight zone at BATS. We then monitored chemical and biological transformations within POM over 6-day dark incubations. We observed transformations of POM carbohydrate composition and microbial communities over time that were remarkably similar to those observed across depth in previous in situ measurements. Additionally, the particle-associated prokaryotic taxa that proliferated during the incubation matched those found on naturally occurring mesopelagic particles at BATS. Our results directly tie naturally occurring particle-associated prokaryotes to observed transformations in POM.
09:45 AM
IDENTIFYING SOURCES AND TRANSFORMATION OF PARTICULATE ORGANIC MATTER IN THE NORTH ATLANTIC SPRING BLOOM USING ISOTOPES, AMINO ACIDS, AND CARBOHYDRATES (9505)
Primary Presenter: Elizabeth Yanuskiewicz, University of Miami (eay10@miami.edu)
In May 2021, the EXPORTS (EXport Processes in the Ocean from RemoTe Sensing) program sampled a declining phytoplankton bloom in the North Atlantic. To understand the overall biogeochemical impact of particle flux during the bloom, including episodic flux of aggregates, questions remain about the chemical composition, sources, and degradative transformation of particulate organic matter (POM). We measured the concentrations of carbohydrate monomers and the concentrations, nitrogen isotope ratios, and carbon isotope ratios of individual amino acids in sinking and suspended particles collected from the surface to mid-mesopelagic (30-500 m) depths and over time during the bloom decline. In the euphotic zone, patterns in the nitrogen isotope ratios of amino acids indicated that POM derived predominantly from primary producers, with nitrogen sources varying across size fractions, and carbon isotopic fingerprints of essential amino acids identified major phytoplankton clades contributing to particle size fractions. Patterns in the nitrogen isotope ratios of amino acids confirm that phytoplankton-derived material persisted into the mesopelagic, but with significant overprinting by microbial degradation. Carbohydrate composition shifted from glucose-dominated in the euphotic zone to more amino-containing and acidic carbohydrates in the mesopelagic, which are components associated with the formation of sinking algal aggregates. We discuss how the observed POM composition may affect the export and dietary potential of sinking particles across the sampling period.
10:00 AM
UVP INVESTIGATION OF BIOTIC AND ABIOTIC FACTORS ON PARTICLE FLUX IN THE SARGASSO SEA (9554)
Primary Presenter: Andrea Brenner, Arizona State University (aebrenne@asu.edu)
The production and sinking of particulate organic carbon (POC) are important biogeochemical processes in marine systems. Understanding the transformations of this organic matter requires an evaluation of both the biotic and abiotic factors that affect particle creation and alteration. Prior research conducted at the Bermuda Atlantic Time-series Study (BATS) station has demonstrated that different particle types vary seasonally in their contribution to POC flux and are influenced by local zooplankton communities. A vertically and temporally detailed understanding of how environmental variables, such as temperature, water density, and chlorophyll concentrations, mediate particle flux, abundance, and morphology remains lacking. This study explores Underwater Vision Profiler (UVP) images collected on monthly oceanographic cruises near the BATS station. From May 2022 to June 2023, we analyzed images of aggregates, cylindrical fecal pellets, and spherical fecal pellets and simultaneously collected environmental data. Particle abundance and vertical distribution vary with temperature and surface chlorophyll, while there was a seasonally apparent midwater peak in particles (near 500 m) that correlates with a region of known migrator biomass. The relative contributions of particle type, optical transparency, and inferred density also change with depth. This work thus provides seasonally and vertically resolved insight into both the abiotic and biotic factors shaping the flux at BATS.
10:15 AM
The remineralization and fate of labile organic nitrogen in marine environments (9420)
Primary Presenter: Zhanfei Liu, The University of Texas at Austin (zhanfei.liu@utexas.edu)
The production of algal biomass and its subsequent remineralization essentially drives elemental cycling and the preservation of a small fraction of organic matter in the ocean. Since proteins account for a major fraction of the algal biomass and half of the algal production is processed by heterotrophic bacteria, understanding bacteria-mediated protein degradation, from extracellular enzymatic hydrolysis, nutrient regeneration to the formation of refractory organic matter, may be one of the key deciphering ocean carbon and nitrogen cycling. While the degradation of organic carbon has been extensively studied, studies on the degradation of organic nitrogen are relatively sporadic. In this study we systemically examined the degradation and fate of small peptides and free amino acids through the 15N labelling technique. Our laboatory incubation results showed that the fraction of refractory organic nitrogen formed is dependent on specific amino acids. For example, our results showed that as much as 45% of valine N was transformed to refractory dissolved organic nitrogen (DON) as compared to 6% for alanine after 3 weeks of incubation. The DON derived from amino acids was further characterized using high resolution liquid chromatography mass spectrometry and the results will be presented. Overall, our results suggested that the formation of refractory DON in the ocean may be related to specific amino acids, and this formation seems to be rapid, in a time scale of weeks.
SS11A - Biotic and abiotic influences on the lability and fate of organic matter
Description
Time: 9:00 AM
Date: 27/3/2025
Room: W207AB