Table of Contents

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

Seawater was collected from Niskin bottles or the ship’s underway system. Samples were processed to obtain the concentrations of dissolved organic carbon and total organic carbon. The seawater for total organic carbon (TOC) was aliquoted directly into a combusted glass vial. For dissolved organic carbon (DOC), seawater was filtered with a 0.2 µM Omnipore filter (Whatman) mounted in a Teflon filter holder into a combusted glass vial. Both types of samples were acidified to pH~3 with concentrated hydrochloric acid (HCl) and stored at 4°C until analysis with a Shimadzu TOC-L. Blanks (MilliQ water) and standard curves with potassium hydrogen phthalate were interspersed into the sample runs. The coefficient of variability between replicate injections was <1%. Comparisons to standards provided by Prof. D. Hansell (University of Miami) were made daily.

- Imported data from source file "Longnecker_NPOCdata.2025.08.20.xlsx" into the BCO-DMO data system.
- Combined the date and time columns into a single ISO datetime UTC value
- Combined the latitude degrees and latitude minutes into a single latitude in decimal degrees
- Combined the longitude degrees and longitude minutes into a single longitude in decimal degrees

NSF Award Abstract:
Microbial production and consumption of organic carbon play critical roles in the marine food web and global carbon cycling. Bacteria release organic matter in a variety of chemical forms and in diverse contexts, ranging from individual molecules to small aggregates and larger biological particles. In recent years we have come to understand that most, if not all, marine microbes release nanoscale structures called extracellular vesicles from their surfaces. These discrete particles, which are abundant in the oceans, are capable of transporting multiple classes of organic molecules between organisms and can serve as a potential nutrient source for other microbes. Extracellular vesicles thus represent a potentially important component of marine microbial food webs, but the magnitude and dynamics of this contribution are unknown. Further, the packaging of material within vesicles may influence the accessibility of this organic material as compared with truly ‘dissolved’ substances to different groups of marine organisms, potentially biasing nutrient exchanges. Broader impacts of this work is providing hands-on research experiences for female undergraduate students - including those from groups historically underrepresented in STEM fields - and training in data analysis tools.

The goal of this project is to advance the understanding of the role that extracellular vesicles play in marine dissolved organic carbon pools and microbial food webs. To determine the contribution of vesicles to organic matter release by marine microbes, the investigators are quantifying the fraction of excreted carbon and nitrogen associated with vesicles released by multiple marine cyanobacteria and heterotrophs. The project is examining how vesicles are ‘consumed’ by heterotrophs to calculate a mass balance of vesicle utilization and produce detailed gene expression data to explore how cells respond to the presence of vesicles. Finally, experiments with coastal and oligotrophic marine communities are providing insights into which organisms utilize vesicles in the field, and whether they are broadly accessible to all microbes or are instead preferentially consumed by a subset of microbes. Collectively, these experiments are opening up a new area of research into the mechanisms underlying the microbial loop and provide foundational insights into the roles of extracellular vesicles in ocean ecosystems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.