Trace-metals from CTD casts and underway water samples collected during the R/V Hugh R. Sharp cruise HRS1414 in the Mid and South-Atlantic Bight in August of 2014 (DANCE project) (NCEI Accession 0277274)

This dataset contains biological, chemical, optical, and physical data collected on R/V Hugh R. Sharp during cruise HRS1414 in the North Atlantic Ocean from 2014-08-01 to 2014-08-10. These data include Ammonium, Fe, depth, fluorescence, nitrate plus nitrite, reactive phosphorus (PO4), salinity calculated from CTD primary sensors, and water temperature. The instruments used to collect these data include CTD Sea-Bird, Fluorometer, Nutrient Autoanalyzer, and UV Spectrophotometer-Shimadzu. These data were collected by Dr Margaret Mulholland and Peter N. Sedwick of Old Dominion University and Dr Raymond Najjar of Pennsylvania State University as part of the "Collaborative Research: Impacts of atmospheric nitrogen deposition on the biogeochemistry of oligotrophic coastal waters (DANCE)" project. The Biological and Chemical Oceanography Data Management Office (BCO-DMO) submitted these data to NCEI on 2023-01-23.

The following is the text of the dataset description provided by BCO-DMO:

Acquisition Description: [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 pumped 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.