Table of Contents

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

Water column samples were collected in July 2023 aboard the R/V Endeavor using a trace metal clean rosette (SeaBird) outfitted with 12-L Niskin-X samplers (Ocean Test Equipment), a trace metal clean pump system, or a custom surface pump “towfish” system (Mellett and Buck, 2020). Seawater samples for macronutrient analysis were filtered through 0.2 µm Pall Acropak Super membrane filter capsules, collected in acid-cleaned and triple-rinsed 15-mL Falcon tubes, stored in ziplock bags and frozen (-20 ºC) until analyzed at Oregon State University following recommended best practices (Becker et al., 2020).

Samples from seawater incubation experiments were filtered through consecutive acid-cleaned 5 µm and 0.4 µm polycarbonate track-etched (PCTE, Whatman) filters in a dual stage Teflon filter rig (Savillex) on a custom acrylic tower. Filtrate was collected in acid-cleaned and triple-rinsed 15-mL Falcon tubes and stored in ziplock bags and frozen (-20 ºC) until analyzed at Oregon State University following recommended practices (Becker et al., 2020).

Samples were analyzed for phosphate, nitrate+nitrite, silicate, and nitrite on a QuAAtro39 AutoAnalyzer (SEAL Analytical) according to standard colorimetric methods (Strickland and Parsons, 1972). All reagents were prepared in dedicated labware with high purity Milli-Q (>18 MΩ cm) water. Working standards were prepared fresh daily in an artificial seawater (ASW; 35 g/L sodium chloride, 0.5 g/L sodium bicarbonate) matrix using calibrated volumetric pipettes.

Nine-point standard curves made in artificial seawater were analyzed at the beginning of each run following a series of reagent blanks. Quality control checks were conducted every twelfth sample using a combination of ASW blanks and standards. The highest standard from the calibration curves was analyzed approximately every twenty samples to check/correct for drift during the runs. Subsamples of reference material for nutrients in seawater (Kanso) were measured in each run (see accompanying Table 1 in supplemental document).

Detection limits for each parameter were determined from three times the standard deviation of replicate analyses of the lowest standards for each parameter. Limits of detection (LOD) were 0.01 µM for phosphate, 0.04 µM for nitrate+nitrite, 0.04 µM for silicate, and 0.01 µM for nitrite. Values below detection are reported as “0” µM with accompanying QC Flag 6. Limits of quantification (LOQ) for each parameter were determined as ten times the standard deviation of replicate analyses of the lowest standards. These are provided in the supplemental document, Table 2, as an alternative estimate of the analytical limitations for these parameters.

Sample analyses for macronutrients were performed by senior researcher Dr. Salvatore Caprara in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University.

Data were flagged using the SeaDataNet quality flag scheme recommended by GEOTRACES (https://www.geotraces.org/geotraces-quality-flag-policy/) and described below. Notes specific to the application of these flags to this dataset are noted in brackets […].

0: No Quality Control: No quality control procedures have been applied to the data value. This is the initial status for all data values entering the working archive. [Not used].

1: Good Value: Good quality data value that is not part of any identified malfunction and has been verified as consistent with real phenomena during the quality control process. [See accompanying Table 1 in supplemental document for certified reference material results obtained in this study].

2: Probably Good Value: Data value that is probably consistent with real phenomena, but this is unconfirmed or data value forming part of a malfunction that is considered too small to affect the overall quality of the data object of which it is a part. [Used when no replicate measurements were available to check the quality of the data].

3: Probably Bad Value: Data value recognized as unusual during quality control that forms part of a feature that is probably inconsistent with real phenomena. [Not used].

4: Bad Value: An obviously erroneous data value. [Not used].

5: Changed Value: Data value adjusted during quality control. Best practice strongly recommends that the value before the change be preserved in the data or its accompanying metadata. [Not used].

6: Value Below Detection Limit: The level of the measured phenomenon was less than the limit of detection (LOD) for the method employed to measure it. The accompanying value is the detection limit for the technique or zero if that value is unknown. [Values below detection are reported as 0 and should be interpreted using the associated quality flag = 6. Detection limits for each parameter are provided in the methods, and calculated limits of detection and limits of quantification are provided in the supplemental document, Table 2].

7: Value in Excess: The level of the measured phenomenon was too large to be quantified by the technique employed to measure it. The accompanying value is the measurement limit for the technique. [Not used].

8: Interpolated Value: This value has been derived by interpolation from other values in the data object. [Not used].

9: Missing Value: The data value is missing. Any accompanying value will be a magic number representing absent data [Used when no data is available for this parameter].

A: Value Phenomenon Uncertain: There is uncertainty in the description of the measured phenomenon associated with the value such as chemical species or biological entity. [Not used].

- Loaded data from BCO-DMO_Buck_STING-II_Nutrients_260206.csv with missing values defined as "", "nd", "na", and "nda"
- Combined DATE_UTC and TIME_UTC fields (format %m/%d/%y and %H:%M) into new DATETIME_UTC column formatted as %Y-%m-%dT%H:%MZ in UTC
- Combined DATE_EST and TIME_EST fields (format %m/%d/%y and %H:%M) into new DATETIME_EDT column formatted as %Y-%m-%dT%H:%M in America/New_York timezone
- Reordered columns into specified sequence with STING_ID through NO2_FLAG
- Converted DATE_UTC field (format %m/%d/%y) to DATE_UTC column formatted as %Y-%m-%d in UTC
- Converted DATE_EST field (format %m/%d/%y) to DATE_EST column formatted as %Y-%m-%d in America/New_York timezone
- Renamed DATE_EST to DATE_EDT and TIME_EST to TIME_EDT
- Output written to 997792_v1_sting_ii_nutrients.csv

NSF Award Abstract:
This project will investigate how groundwater discharge delivers important nutrients to the coastal ecosystems of the West Florida Shelf. Preliminary studies indicate that groundwater may supply both dissolved organic nitrogen (DON) and iron in this region. In coastal ecosystems like the West Florida Shelf that have very low nitrate and ammonium concentrations, DON is the main form of nitrogen available to organisms. Nitrogen cycling is strongly affected by iron availability because iron is essential for both photosynthesis and for nitrogen fixation. This study will investigate the sources and composition of DON and iron, and their influence on the coastal ecosystem. The team will sample offshore groundwater wells, river and estuarine waters, and conduct two expeditions across the West Florida Shelf in winter and summer. Investigators will participate in K-12 and outreach activities to increase awareness of the project and related science. The project will fund the work of six graduate and eight undergraduate students across five institutions, furthering NSF’s goals of education and training.

Motivated by preliminary observations of unexplained, tightly-correlated DON and dissolved iron concentrations across the West Florida Shelf (WFS), the proposed work will quantify the flux and isotopic signatures of submarine groundwater discharge (SGD)-derived DON and iron to the WFS, and evaluate the bioavailability of this temporally-variable source using four seasonal near-shore campaigns sampling offshore groundwater wells, estuarine, and riverine endmembers and two cross-shelf cruises. The work will evaluate whether SGD stimulates nitrogen fixation on the WFS, and the potential for the stimulated nitrogen fixation to further modify the chemistry of DON and dissolved iron in the region. The cross-shelf cruises will investigate hypothesized periods of maximum SGD and Trichodesmium abundance (June), and reduced river discharge and SGD (February), thus comparing two distinct biogeochemical regimes. The concentrations and isotopic compositions of DON and dissolved iron, molecular composition of DON, and the concentration and composition of iron-binding ligands will be characterized. Nitrogen fixation rates and Trichodesmium spp. abundance and expression of iron stress genes will be measured. Fluxes of DON and iron from SGD and rivers will be quantified with radium isotope mass balances. The impacts of SGD on nitrogen fixation and DON/ligand production will be constrained with incubations of natural phytoplankton communities with submarine groundwater amendments. Two hypotheses will be tested: 1) SGD is the dominant source of bioavailable DON and dissolved iron on the WFS, and 2) SGD-alleviation of iron stress changes the dominant Trichodesmium species on the WFS, increases nitrogen fixation rates and modifies DON and iron composition. Overall, the work will establish connections between marine nitrogen and iron cycling and evaluate the potential for coastal inputs to modify water along the WFS before export to the Atlantic Ocean. This study will thus provide a framework to consider these boundary fluxes in oligotrophic coastal systems and the relative importance of rivers and SGD as sources of nitrogen and iron in other analogous locations, such as coastal systems in Australia, India, and Africa, where nitrogen fixation and SGD have also been documented.

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.