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

This dataset is derived from Selden et al. (2024) JGR Oceans Table S1, and McGillicuddy bottle data from TN368, the third SPIROPA cruise (https://www.bco-dmo.org/dataset/849340). The mean values of nitrogen fixation rates shown here are derived from nitrogen fixation incubation data (https://www.bco-dmo.org/dataset/928568)

Glossary of terms:
A = Atom-% enrichment
APN = Atom-% enrichment of the particulate nitrogen pool 
BDL = Below detection limit
DNQ = Detectable but not quantifiable
LOD = Limit of detection
LOQ = Limit of quantification 
N2 = Nitrogen gas
PETG = Polyethylene Terephthalate Glycol
PN = Particulate nitrogen
NFR = Nitrogen fixation rate
SUR = Specific uptake rate
t0 = time initial
tf = time final

Specific N₂ uptake rates (SUR) were calculated following Montoya et al. (1996):

Equation 1:       SUR = (APN_tf - APN_t0) / (AN2 - APN_t0) ] x (1/time)

where A represents the atom-% enrichment of the initial (t=0) or final (t=f) particulate nitrogen (PN) pool, or the nitrogen (N₂) pool. Across all experiments, AN2 averaged 3.89 ± 2.0%. Experiments with <1% enrichment were excluded from downstream analysis. The specific uptake rate represents the relative contribution of diazotroph-derived N to PN turnover within a given sample. Absolute N₂ fixation rates (NFR) were calculated as:

Equation 2:       NFR = SUR x [PN]

where [PN] indicates the particulate nitrogen concentration. Limits of detection and quantification were calculated per incubation by propagating the minimum detectable difference between initial and final ¹⁵N atom-% enrichment of the PN pool (3σ and 10σ), three sigma and ten sigma respectively, n≥7, 12.5 µg N standards measured daily through Eqn. 2 (Ripp, 1996; White et al. 2020). A rate was only considered detectable if two of three replicate incubations yielded detectable rates.

- Imported data from source file "Selden_JGR24_TableS1.xlsx" into the BCO-DMO data system.
- Changed date format from m/d/yyyy to yyyy-mm-dd (ISO Date 8601 format) and converted datetimes from EST to UTC.
- Converted latitude and longitude to decimal degrees.
- Added official cruise ID corresponding to the the provided deployment and cruise name
- Added cast number and replicate sample ids (from the incubations) based on datetime and depth.
- Rounded values according to the PI’s/submitter’s indicated precision
- Modified parameter (column) names to conform with BCO-DMO naming conventions. The only allowed characters are A-Z,a-z,0-9, and underscores. No spaces, hyphens, commas, parentheses, or Greek letters.

NSF award abstract:

The continental shelf break of the Middle Atlantic Bight supports a productive and diverse ecosystem. Current paradigms suggest that this productivity is driven by several upwelling mechanisms at the shelf break front. This upwelling supplies nutrients that stimulate primary production by phytoplankton, which in turn leads to enhanced production at higher trophic levels. Although local enhancement of phytoplankton biomass has been observed in some circumstances, such a feature is curiously absent from time-averaged measurements, both from satellites and shipboard sampling. Why would there not be a mean enhancement in phytoplankton biomass as a result of the upwelling? One hypothesis is that grazing by zooplankton prevents accumulation of biomass on seasonal and longer time scales, transferring the excess production to higher trophic levels and thereby contributing to the overall productivity of the ecosystem. However, another possibility is that the net impact of these highly intermittent processes is not adequately represented in long-term means of the observations, because of the relatively low resolution of the in-water measurements and the fact that the frontal enhancement can take place below the depth observable by satellite. The deployment of the Ocean Observatories Initiative (OOI) Pioneer Array south of New England has provided a unique opportunity to test these hypotheses. The combination of moored instrumentation and autonomous underwater vehicles will facilitate observations of the frontal system with unprecedented spatial and temporal resolution. This will provide an ideal four-dimensional (space-time) context in which to conduct a detailed study of frontal dynamics and plankton communities needed to examine mechanisms controlling phytoplankton populations in this frontal system. This project will also: (1) promote teaching, training and learning via participation of graduate and undergraduate students in the research , (2) provide a broad dissemination of information by means of outreach in public forums, printed media, and a video documentary of the field work, and (3) contribute to improving societal well-being and increased economic competitiveness by providing the knowledge needed for science-based stewardship of coastal ecosystems, with particular emphasis on connecting with the fishing industry through the Commercial Fisheries Research Foundation.

The investigators will conduct a set of three cruises to obtain cross-shelf sections of physical, chemical, and biological properties within the Pioneer Array. Nutrient distributions will be assayed together with hydrography to detect the signature of frontal upwelling and associated nutrient supply. The investigators expect that enhanced nutrient supply will lead to changes in the phytoplankton assemblage, which will be quantified with conventional flow cytometry, imaging flow cytometry (Imaging FlowCytobot, IFCB), optical imaging (Video Plankton Recorder, VPR), traditional microscopic methods, and pigment analysis. Zooplankton will be measured in size classes ranging from micro- to mesozooplankton with the IFCB and VPR, respectively, and also with microscopic analysis. Biological responses to upwelling will be assessed by measuring rates of primary productivity, zooplankton grazing, and net community production. These observations will be synthesized in the context of a coupled physical-biological model to test the two hypotheses that can potentially explain prior observations: (1) grazer-mediated control and (2) undersampling. Hindcast simulations will also be used to diagnose the relative importance of the various mechanisms of upwelling. The intellectual merit of this effort stems from our interdisciplinary approach, advanced observational techniques, and integrated analysis in the context of a state-of-the-art coupled model. The project will address longstanding questions regarding hydrodynamics and productivity of an important ecosystem, leading to improved understanding of physical-biological interactions in a complex continental shelf regime. Given the importance of frontal systems in the global coastal ocean, it is expected that knowledge gained will have broad applicability beyond the specific region being studied.