Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Collection

Water was collected via Niskin bottles mounted on a rosette, equipped with a CTD. Seawater was transferred to carboys that were rinsed three times with water from the sampling depth and then filled with seawater from a single Niskin bottle.

Particulate organic matter (POM) was harvested by filtering between 5-15 liters of seawater through a 47-mm pre-combusted (400℃ for 6 hours) glass fiber filter (GF/F; nominal pore size 0.7 μm; for volumes filtered at each depth and station, see the dataset). Filers were stored at -80C until further analysis. The same filter was used for both particulate organic carbon (POC) measurements and monosaccharide composition analysis.   

Analysis

Particulate organic carbon was measured as described in Becker et al. (2020). In brief, triplicate filter punches from samples collected on pre-combusted (400℃ for 6 hours) glass fiber filters (GF/F) were placed in an acidic environment (concentrated HCl fumes) for 24 h to remove inorganic carbon. After drying for 24 h at 60 °C, the samples were packed in pre-combusted tin foil. C was quantified using an elemental analyzer (cario MICRO cube; Elementar Analysensysteme) using sulfanilamide for calibration. Limits of detection for POC was 0.001 mg C/L, based on the standard deviation of blank measurements.

The monosaccharide constituents of total combined carbohydrates (i.e., polysaccharides, glycoproteins, glycolipids, etc.) of POM (collected as described above) were determined from triplicate filter punches (11.2 mm diameter). Samples were acid hydrolyzed by adding 1 M HCl to each filter piece, flame sealing each piece in a glass ampule, and placing the ampules in an oven at 100°C for 24 hours. After acid hydrolysis, the samples were dried on a speed-vac and resuspended in Milli-Q water to remove any HCl. The quantity and composition of the resulting monosaccharides were measured using a modified protocol (Engel and Handel (2011), as described by Vidal-Melgosa et al. (2021)). In brief, neutral, amino, and acidic sugars were quantified using high performance anion exchange chromatography on a Dionex ICS-5000+ system with pulsed amperometric detection (HPAEC-PAD). Peaks were identified using retention times of purified monosaccharide standards; abundance was quantified from standards using the peak area for a given monosaccharide. The limit of detection for monosaccharides varied from 0.5 – 1 ug/L, depending on the specific monosaccharide measured.

Data processed using Microsoft Excel.

- Imported "20250721_EN638_POC_and_Monosaccharide_BCODMO.csv" into the BCO-DMO system
- Converted "date" and "time" to one date time parameter, "ISO_DateTime_EST"
- Created a new datetime parameter in UTC "ISO_DateTime_UTC"
- Removed "date" and "time" as redundant
- Replaced special characters and units in parameter names, based on BCO-DMO guidelines
- Exported file as "985784_v1_en638_poc_monosaccharide.csv"

NSF Award Abstract:
Marine dissolved organic matter (DOM) is one of the largest actively-cycling reservoirs of organic carbon on the planet, and thus a major component of the global carbon cycle. The high molecular weight (HMW) fraction of DOM is younger in age and more readily consumed by microbes than lower molecular weight (LMW) fractions of DOM, but the reasons for this difference in reactivity between HMW DOM and LMW DOM are unknown. Two factors may account for the greater reactivity of HMW DOM: (i) targeted uptake of HMW DOM by specific bacteria, a process the PI and her collaborators at the Max Planck Institute for Marine Microbiology (MPI) recently identified in surface ocean waters; and (ii) a greater tendency of HMW DOM to aggregate and form gels and particles, which can be colonized by bacteria that are well-equipped to breakdown organic matter. Scientists and students from the University of North Carolina (UNC) - Chapel Hill will collaborate with researchers at the MPI for Marine Microbiology (Bremen, Germany) to investigate this breakdown of HMW DOM by marine microbial communities. These investigations will include a field expedition in the North Atlantic, during which HMW DOM degradation rates and patterns will be compared in different water masses and under differing conditions of organic matter availability. DOM aggregation potential, and degradation rates of these aggregates, will also be assessed. Specialized microscopy will be used in order to pinpoint HMW DOM uptake mechanisms and rates. The work will be complemented by ongoing studies of specific bacteria that breakdown HMW DOM, their genes, and their proteins. Graduate as well as undergraduate students will participate as integral members of the research team in all aspects of the laboratory and field work; aspects of the project will also be integrated into classes the scientist teaches at UNC.

The existence of a size-reactivity continuum of DOM - observations and measurements showing that HMW DOM tends to be younger and more reactive than lower MW DOM - has been demonstrated in laboratory and field investigations in different parts of the ocean. A mechanistic explanation for the greater reactivity of HMW DOM has been lacking, however. This project will investigate the mechanisms and measure rates of HMW DOM degradation, focusing on identifying the actors and determining the factors that contribute to rapid cycling of HMW DOM. Collaborative work at UNC and MPI-Bremen recently identified a new mechanism of HMW substrate uptake common among pelagic marine bacteria: these bacteria rapidly bind, partially hydrolyze, and transport directly across the outer membrane large fragments of HMW substrates that can then be degraded within the periplasmic space, avoiding production of LMW DOM in the external environment. This mode of substrate processing has been termed selfish, since targeted HMW substrate uptake sequesters resources away from other members of microbial communities. Measurements and models thus must account for three modes of substrate utilization in the ocean: selfish, sharing (external hydrolysis, leading to low molecular weight products), and scavenging (uptake of low molecular weight hydrolysis products without production of extracellular enzymes). Using field studies as well as mesocosm experiments, the research team will investigate the circumstances and locations at which different modes of substrate uptake predominate. A second focal point of the project is to determine the aggregation potential and microbial degradation of aggregated HMW DOM. Preliminary studies have demonstrated that particle-associated microbial communities utilize a broader range of enzymatic capabilities than their free-living counterparts. These capabilities equip particle-associated communities to effectively target a broad range of complex substrates. The project will thus focus on two key aspects of HMW DOM - the abilities of specialized bacteria to selectively sequester HMW substrates, as well as the greater potential of HMW substrates to aggregate ? and will quantify these factors at different locations and depths in the ocean. The project will thereby provide a mechanistic underpinning for observations of the DOC size-reactivity continuum, an essential part of developing an overall mechanistic understanding of organic matter degradation in the ocean.