Table of Contents

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

Particulate Carbon and Nitrogen (PNPC)

Whole water from three target depths (near surface, the depth above the Chl maximum (or near the bottom of the mixed layer), and the depth of the Chl maximum) at each station was collected from Niskin bottles into 10 L carboys and transported to the on-board laboratory where water samples were mixed and sub-samples (0.2–1.4 L) were collected onto pre-combusted GF-75 filters (Whatman®, nominal pore size 0.3 μm) in triplicate, for analysis of particulate nitrogen (PN) and carbon (PC) concentrations and the natural abundance of 15N and 13C. The filters were stored in cryovials and immediately frozen and stored in a freezer at -20 °C until analysis. Prior to their analysis, filters were dried at 40 ºC, pelletized in tin capsules, and analyzed on a Europa 20/20 isotope ratio mass spectrometer equipped with an automated N and C analyzer. The detection limit of the mass spectrometer was 0.0018 and 0.0005 atom% for 15N and 13C, respectively; these values were derived based on three times the standard deviation (3 × SD) of the atom% of 12.5 µg N and 100 µg C standards (n=40).

Nitrogen Uptake 

Parallel sets of triplicate whole water (0.5−2 L) from the three target depths mentioned above (near surface, above the depth of the Chl maximum (or near the bottom of the mixed layer), and at the depth of the Chl maximum) from 27 stations were dispensed from 10 L carboys into acid-cleaned polyethylene terephthalate glycol incubation bottles (NalgeneTM).

Nitrogen uptake incubations were initiated by amending incubation bottles with highly enriched (98−99%) 15N-labeled substrates (Cambridge Isotope Laboratories, Inc., USA), including ammonium chloride (15NH4Cl), potassium nitrate (K15NO3), potassium nitrite (K15NO2), and 15N- and 13C-labeled potassium cyanate (KO13C15N), urea (13CO(15NH2)2), and algal amino acid mixture.

Nitrogen update rates were calculated via the formula included in the supplemental files section of this metadata landing page. 

Within this formula, (atom% PN)initial and (atom% PN)final represent the 15N isotopic composition of the particulate pool at the initial and final time points of the incubation period; atom% N source pool is the 15N isotopic enrichment of the dissolved nitrogen pool after the tracer addition; [PN] represents the concentration of the particulate nitrogen pool; here, we used the average value between the initial and final PN concentrations for this calculation.

- Converted date values from %m/%d/%Y format to %Y-%m-%d format

NSF Award Abstract:

Nitrogen is a critical nutrient in the world's oceans because, among other things, it is a major component of living organisms and can be a driver in primary productivity. Nitrogen is present in the ocean in a number of organic and inorganic forms, which vary in their ease in being assimilated by marine organisms. Cyanate is a simple form of organic nitrogen present in the ocean, although its abundance and importance to the ocean nitrogen cycle is poorly understood. Using newly developed and tested methods for measuring ambient cyanate concentrations and its uptake in seawater, researchers will analyze the distribution, sources, and geochemistry of cyanate in shelf waters of the Atlantic Ocean. Results from this project will elucidate the importance of cyanate in the marine nitrogen cycle and transform understanding of cyanate production and assimilation in the sea. This project will provide a unique opportunity for both graduate student research and undergraduate training, and will likely expose underrepresented groups to marine sciences.

Although physiological and genomic evidence suggest that marine microbes can utilize a broad array of inorganic and organic nitrogen compounds, cyanate's role in the marine nitrogen cycle has not yet been examined. As one of the simplest organic nitrogen compounds, cyanate has likely been present in the environment over Earth's long history. Evidence suggests that cyanate metabolism appeared early on in bacterial genomes and thus, the study of cyanate assimilation in the contemporary ocean may illuminate microbial processes with deep evolutionary roots. However, a decade since discovering the genomic capacity for cyanate utilization in marine cyanobacteria, little is still known about cyanate distributions in the environment, how it is produced, and how widespread cyanate utilization is among marine microbes. To further understanding of cyanate's role in the marine nitrogen cycle, a combination of geochemical approaches will be used to assess: 1) the distribution of cyanate in the marine environment, 2) potential sources of cyanate and the timescales at which cyanate is produced, 3) the rate of cyanate removal via microbial uptake and spontaneous decomposition, and 4) the geochemical coupling between cyanate production and consumption. Results generated from this study will be important for augmenting knowledge of the marine nitrogen cycle, refining biogeochemical models, and further understanding of the functioning of marine microbial communities.