Table of Contents

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

[The following methodology applies where dataset parameter "sample_source" is "UNDERWAY"]

Near-surface sample collection: Near-surface (~4 m depth) seawater was collected whilst underway at ~5 knots using a trace-metal clean towfish system [Sedwick et al., 2011]. The subsamples for analysis of DFe, NO3+NO2, PO4 were taken directly from the towfish line, after filtration through a 0.8/0.2 µm AcroPak Supor filter capsule (Pall), in acid-cleaned 125 mL low-density polyethylene bottles (Nalgene) for shore-based DFe determinations, and 60 mL polypropylene tubes (Falcon) for shipboard NO3+NO2, PO4 and NH4 analyses.

Near-surface underway measurements: Continuous underway measurements of near-surface seawater temperature, salinity and chlorophyll fluorescence were made using the ship's underway seawater supply, which is pumed from a water depth of ~1m. The data presented correspond to the approximate times when subsamples were collected from the towfish seawater outlet for measurements of dissolved iron and macronutrients (see above).

DFe: Filtered seawater samples were acidified at-sea to pH ~1.8 with Fisher Optima grade ultrapure hydrochloric acid, and then stored at room temperature until post-cruise analysis at Old Dominion University. Dissolved iron was determined by flow injection analysis with colorimetric detection after in-line preconcentration on resin-immobilized 8-hydroxyquinoline (Sedwick et al., 2015), using a method modified from Measures et al. (1995). Analyses were performed on a volumetric basis, so concentrations are reported in units of nanomole liter-1 (nM). Analytical precision is estimated from multiple (separate-day) determinations of the SAFe seawater reference materials, which yield uncertainties (expressed as one relative standard deviation on the mean, or one sigma) of ~15% at the concentration level of SAFe S seawater (0.090 nM), and ~10% at the concentration level of SAFe D2 seawater (0.90 nM). The analytical limit of detection is estimated as the DFe concentration equivalent to a peak area that is three times the standard deviation on the zero-loading blank (manifold blank), which yields an estimated detection limit below 0.04 nM (Bowie et al., 2004). Blank contributions from the ammonium acetate sample buffer solution (added on-line during analysis) and hydrochloric acid (added after collection) are negligible.

NO3+NO2: Dissolved nitrate and nitrite was determined at sea using an Astoria Pacific nutrient autoanalyzer using standard colorimetric methods with an estimated detection limit of 0.14 µM (Parsons et al., 1984; Price and Harrison, 1987). In surface waters, nitrate and nitrite were determined using the same autoanalyzer equipped with a liquid waveguide capillary cell (World Precision Instruments) (Zhang, 2000) to achieve an estimated detection limit of 0.02 µM.

PO4: Dissolved phosphate was determined at sea using an Astoria Pacific nutrient autoanalyzer using standard colorimetric methods with an estimated detection limit of 0.03 µM (Parsons et al., 1984; Price and Harrison, 1987).

NH4: Dissolved ammonium was determined at sea using the manual orthophthaldialdehyde method (Holmes et al., 1999), with an estimated detection limit of 10 nM.

Temperature: Underway temperature was measured using a conductivity-temperature-depth sensor (SBE 45, SeaBird Electronics).

Salinity: Underway salinity was calculated from in-situ conductivity, as measured using a conductivity-temperature-depth (CTD) sensor (SBE 45, SeaBird Electronics).

Fluorescence: Underway chlorophyll fluorescence was measured using a Turner AU10 fluorometer.

[The following methodology applies where dataset parameter "sample_source" is "CTD"]

Water column sample collection and in-situ measurements: Water-column samples for analysis of dissolved iron, nitrate plus nitrite, phosphate and ammonium, and continuous profiles of temperature, salinity and chlorophyll fluorescence were collected using a trace-metal clean conductivity-temperature-depth sensor (SBE 19 plus, SeaBird Electronics) mounted on a custom-built trace-metal clean carousel (SeaBird Electronics) fitted with custom-modified 5-L Teflon-lined external-closure Niskin-X samplers (General Oceanics), deployed on a Kevlar line. Upon recovery, the Niskin-X samplers were transferred into a shipboard Class-100 clean laboratory, where seawater was filtered through pre-cleaned 0.2-µm pore AcroPak Supor filter capsules (Pall) into acid-cleaned 125 mL low-density polyethylene bottles (Nalgene) for shore-based dissolved iron determinations, and 60 mL polypropylene tubes (Falcon) for shipboard nutrient analyses.

DFe: Filtered seawater samples were acidified at-sea to pH ~1.8 with Fisher Optima grade ultrapure hydrochloric acid, and then stored at room temperature until post-cruise analysis at Old Dominion University. Dissolved iron was determined by flow injection analysis with colorimetric detection after in-line preconcentration on resin-immobilized 8-hydroxyquinoline (Sedwick et al., 2015), using a method modified from Measures et al. (1995). Analyses were performed on a volumetric basis, so concentrations are reported in units of nanomole liter-1 (nM). Analytical precision is estimated from multiple (separate-day) determinations of the SAFe seawater reference materials, which yield uncertainties (expressed as one relative standard deviation on the mean, or one sigma) of ~15% at the concentration level of SAFe S seawater (0.090 nM), and ~10% at the concentration level of SAFe D2 seawater (0.90 nM). The analytical limit of detection is estimated as the DFe concentration equivalent to a peak area that is three times the standard deviation on the zero-loading blank (manifold blank), which yields an estimated detection limit below 0.04 nM (Bowie et al., 2004). Blank contributions from the ammonium acetate sample buffer solution (added on-line during analysis) and hydrochloric acid (added after collection) are negligible.

NO3+NO2: Dissolved nitrate and nitrite was determined at sea using an Astoria Pacific nutrient autoanalyzer using standard colorimetric methods with an estimated detection limit of 0.14 µM (Parsons et al., 1984; Price and Harrison, 1987). In surface waters, nitrate and nitrite were determined using the same autoanalyzer equipped with a liquid waveguide capillary cell (World Precision Instruments) (Zhang, 2000) to achieve an estimated detection limit of 0.02 µM.

PO4: Dissolved phosphate was determined at sea using an Astoria Pacific nutrient autoanalyzer using standard colorimetric methods with an estimated detection limit of 0.03 µM (Parsons et al., 1984; Price and Harrison, 1987).

NH4: Dissolved ammonium was determined at sea using the manual orthophthaldialdehyde method (Holmes et al., 1999), with an estimated detection limit of 10 nM.

Temperature: In-situ temperature was measured using a conductivity-temperature-depth sensor (SBE 19 plus, SeaBird Electronics).

Salinity: Salinity was calculated from in-situ conductivity, as measured using a conductivity-temperature-depth (CTD) sensor (SBE 19 plus, SeaBird Electronics).

Fluorescence: In-situ chlorophyll fluorescence was measured using a WET Labs ECO-FL(RT)D deep chlorophyll fluorometer with 125 μg L-1 range mounted on the CTD rosette.

CTD data (temperature, salinity) were processed using SeaSoft processing software (SeaBird Electronics).

BCO-DMO Data Manager Processing Notes:
* added a conventional header with dataset name, PI name, version date
* modified parameter names to conform with BCO-DMO naming conventions
* combined two Excel files, one for the underway data and one for the ctd data into one dataset.
* missing data shown as default missing data identifier "nd" for "no data" or "BDL" for below detection limit.

NSF abstract:

Deposition of atmospheric nitrogen provides reactive nitrogen species that influence primary production in nitrogen-limited regions. Although it is generally assumed that these species in precipitation contributes substantially to anthropogenic nitrogen loadings in many coastal marine systems, its biological impact remains poorly understood. Scientists from Pennsylvania State University, William & Mary College, and Old Dominion University will carry out a process-oriented field and modeling effort to test the hypothesis that deposits of wet atmospheric nitrogen (i.e., precipitation) stimulate primary productivity and accumulation of algal biomass in coastal waters following summer storms and this effect exceeds the associated biogeochemical responses to wind-induced mixing and increased stratification caused by surface freshening in oligotrophic coastal waters of the eastern United States. To attain their goal, the researchers would perform a Lagrangian field experiment during the summer months in coastal waters located between Delaware Bay and the coastal Carolinas to determine the response of surface-layer biogeochemistry and biology to precipitation events, which will be identified and intercepted using radar and satellite data. As regards the modeling effort, a 1-D upper ocean mixing model and a 1-D biogeochemical upper-ocean will be calibrated by assimilating the field data obtained a part of the study using the adjoint method. The hypothesis will be tested using sensitivity studies with the calibrated model combined with in-situ data and results from the incubation experiments. Lastly, to provide regional and historical context for the field measurements and the associated 1-D modeling, linked regional atmospheric-oceanic biogeochemical modeling will be conducted.

Broader Impacts. Results from the study would be incorporated into class lectures for graduate courses on marine policy and marine biogeochemistry. One graduate student from Pennsylvania State University, one graduate student from the College of William and Mary, and one graduate and one undergraduate student from Old Dominion University would be supported and trained as part of this project.