Dataset: BAIT Bottle Data from Trace-metal CTD Casts
Deployment: AE1909

Data are from samples collected during the four cruises of the BAIT project (all were piggybacked on the regular BATS program cruises), EN631, AE1909, AE1921, AE1930.

Water-column samples for trace metal measurements were collected from the Bermuda Atlantic Time-series Study (BATS) site (31°40'N, 64°10'W) and adjacent BATS spatial stations during cruises in March (spring), May (early summer), August (late summer), and November (fall) 2019 aboard R/V Atlantic Explorer and R/V Endeavor. The seawater samples and hydrographic data 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-liter (L) Teflon-lined external-closure Niskin-X samplers (General Oceanics) and deployed on an Amsteel non-metallic line. On the August cruise, we also collected near-surface samples (~0.3 meters (m) depth) in a Niskin-X sampler deployed from an inflatable dinghy ~500 m upwind of the research vessel, to avoid contamination from the ship.

After recovery, the seawater samples were filtered through pre-cleaned 0.2-micrometer (μm) pore AcroPak Supor filter capsules (Pall) using filtered nitrogen gas inside a shipboard clean laboratory (Sedwick et al., 2020, 2022). For analysis of dissolved iron (DFe) and dissolved manganese (DMn), the seawater filtrate was collected in acid-cleaned 125-milliliter (mL) low-density polyethylene (LDPE) bottles (Nalgene) and acidified to pH 1.7 post-cruise by addition of 6 M ultrapure hydrochloric acid (Fisher Optima). For analysis of dissolved aluminum (DAl), the seawater filtrate was collected in acid-cleaned 100 mL LDPE bottles (Bel-Art) and acidified to pH 1.7 post-cruise by addition of 6 M ultrapure hydrochloric acid (Fisher Optima). For dissolved macronutrient determinations, 40 mL of seawater filtrate was collected in sample-rinsed 50 mL polypropylene Falcon tubes (Becton Dickinson) and then stored at -20 degrees Celsius (°C) until analysis. For analysis of soluble iron (sFe) and soluble manganese (sMn), the 0.2 µm seawater filtrate was subsequently filtered through 0.02 µm Anotop syringe filters (Whatman) that were pre-rinsed with dilute hydrochloric acid followed by sample, using a peristaltic pump (Ussher et al. 2010); the resulting 0.02 µm filtrate was stored in acid-cleaned 60 mL LDPE bottles (Nalgene) and acidified to pH 1.7 post-cruise by addition of 6 M ultrapure hydrochloric acid (Fisher Optima).

Concentrations of DFe, sFe, DMn and sMn were determined in the acidified seawater filtrate using inductively-coupled plasma mass spectrometry (ICP-MS, Thermo Fisher Scientific ElementXR), with in-line separation-preconcentration (Elemental Scientific SeaFAST SP3) modified after Lagerström et al. (2013). Calibration standards were prepared in low-analyte concentration filtered seawater for which initial concentrations were determined using the method of standard additions. Calibration standards were introduced using the same in-line separation-preconcentration procedure as the seawater filtrate samples, with yttrium was used as an internal standard for all samples except where indicated. Analytical blank concentrations were assessed by applying the in-line separation-preconcentration procedure including all reagents and loading air in place of the seawater filtrate sample ("air blank"), yielding mean blank concentrations that were not statistically different from zero: -0.006 ± 0.0178 nanomolar (nM) for DFe (n = 62), and -0.007 ± 0.010 nM for DMn (n = 46). Analytical limits of detection, defined as the concentrations equivalent to three times the standard deviation on the mean blank, were 0.054 nM DFe and 0.030 nM for DMn. These same blanks and limits of detection are assumed to apply to sFe and sMn, respectively. Mean concentrations of multiple, separate-day determinations of the GEOTRACES GSP seawater consensus material were 0.177 ± 0.030 nM DFe (n = 10) and 0.795 ± 0.023 nM DMn (n = 13), which are within the analytical uncertainties (defined by ± one standard deviation on the mean) of the current consensus concentrations of 0.155 ± 0.045 nM and 0.778 ± 0.034 nM, respectively. Analytical precision at the concentration levels of the GSP consensus material, expressed as ± one relative standard deviation on the mean, are ± 17% for DFe and ± 2.9% for DMn.

Concentrations of DAl were determined in the acidified sewater filtrate using flow injection analysis with fluorometric detection, without in-line preconcentration, following the method of Resing & Measures (1994). Multiple, separate-day determinations of one of the samples of lowest concentration yielded a mean DAl concentration of 3.19 ± 0.68 nM (n = 12), indicating an estimated analytical uncertainty of ± 21% (expressed as ± one relative standard deviation on the mean). Multiple, separate-day analyses of the GEOTRACES GSP seawater consensus material yielded a mean DAl concentration of 1.52 ± 0.28 nM (n = 6), although there is so far no consensus concentration available for this material. In the absence of a reagent blank for this direct flow injection analysis method, a conservative estimate of the analytical limit of detection is three times the standard deviation on the mean DAl concentration of the low-concentration GSP seawater consensus material, which yields 0.84 nM.

Concentrations of the dissolved inorganic macronutrients nitrate+nitrite (NO3-+NO2-), orthophosphate (PO43-) and reactive silicate (Si) were determined at the Bermuda Institute of Ocean Sciences using continuous flow analysis following the protocols of the Bermuda Atlantic Time-series Study (BATS, 2023). Limits of detection, defined as the concentrations equivalent to three times the standard deviation on the mean baseline signal, are 0.03 micromolar (µM) for NO3-+NO2-, PO43- and Si. Accuracy was verified by the analysis of the KANSO seawater certified reference material during each analytical run.

In-situ temperature was measured using a conductivity-temperature-depth sensor (SBE 19 plus, SeaBird Scientific), with data processed using the SBE Data Processing software. Salinity was calculated from in-situ conductivity, as measured using a conductivity-temperature-depth (CTD) sensor (SBE 19 plus, SeaBird Electronics), with data processed using the SBE Data Processing software. In-situ chlorophyll fluorescence was measured using a WET Labs ECO-FL(RT)D deep chlorophyll fluorometer with 125 micrograms per liter (μg L-1) range mounted on the CTD rosette, with data processed using the SBE Data Processing software. In-situ dissolved oxygen concentration was measured using an SBE 43 Dissolved Oxygen Sensor mounted on the CTD rosette, with data processed using the SBE Data Processing software.