Table of Contents

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

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.

Inductively-coupled plasma mass spectrometer: Instrumental data were collected using ElementXR processing software (Thermo Fisher Scientific), and post-analysis calculations were performed using Microsoft Excel.

Fluorescence detector for flow-injection analysis: After analog-to-digital conversion, peak areas were integrated using FCS software (Graeme Cross), and post-analysis calculations were performed using Microsoft Excel.

CTD sensors: Primary and derived data from the CTD sensors (temperature, conductivity, depth, in-situ chlorophyll fluorescence, dissolved oxygen) were processed using using the SBE Data Processing software (SeaBird Scientific).

Quality Flags:
Data quality flags are provided in the data to denote the following:
1 = good;
2 = likely contaminated or questionable;
3 = questionable because analysis used scandium as an internal standard;
4 = not determined;
5 = below detection.

GEOTRACES Parameter Names:
These data sets have been registered via GEOTRACES DoOR, with the following associated bar codes:

Cruise EN361 (BAIT-I):
- NO2+NO3_D_CONC_BOTTLE::nrjw8v
- PHOSPHATE_D_CONC_BOTTLE::bgaawx
- Mn_S_CONC_BOTTLE::lu1p7p
- Al_D_CONC_BOTTLE::nyicgx
- Fe_D_CONC_BOTTLE::qgisg0
- Mn_D_CONC_BOTTLE::up0xno
- Fe_S_CONC_BOTTLE::a5pzjt
- SILICATE_D_CONC_BOTTLE::idjbwe
- CTDTMP_UP_T_VALUE_SENSOR::v2sf9w
- CTDSAL_UP_D_CONC_SENSOR::fwn2wq

Cruise AE1909 (BAIT-II):
- Mn_D_CONC_BOTTLE::llr9fa
- NO2+NO3_D_CONC_BOTTLE::xwogud
- Fe_S_CONC_BOTTLE::w2gse0
- Al_D_CONC_BOTTLE::6i6r0c
- PHOSPHATE_D_CONC_BOTTLE::ucjrky
- SILICATE_D_CONC_BOTTLE::19bitw
- Fe_D_CONC_BOTTLE::qrejkj
- Mn_S_CONC_BOTTLE::pmuw6o
- CTDTMP_UP_T_VALUE_SENSOR::s7ovrk
- CTDSAL_UP_D_CONC_SENSOR::rddj9l

Cruise AE1921 (BAIT-III):
- Mn_S_CONC_BOTTLE::z49awl
- Fe_D_CONC_BOTTLE::k9zqca
- Al_D_CONC_BOTTLE::tzsmv1
- NO2+NO3_D_CONC_BOTTLE::12l4cd
- Fe_S_CONC_BOTTLE::aoxogq
- SILICATE_D_CONC_BOTTLE::tizucw
- Mn_D_CONC_BOTTLE::tgpx8g
- PHOSPHATE_D_CONC_BOTTLE::mftrbt
- CTDTMP_UP_T_VALUE_SENSOR::cg4pcl
- CTDSAL_UP_D_CONC_SENSOR::9p9jgp

Cruise AE1930 (BAIT-IV):
- Mn_D_CONC_BOTTLE::e9h8va
- SILICATE_D_CONC_BOTTLE::cf3hyt
- Al_D_CONC_BOTTLE::u1ydd2
- Fe_S_CONC_BOTTLE::ynhtgd
- NO2+NO3_D_CONC_BOTTLE::kidyhy
- Mn_S_CONC_BOTTLE::cpgrz2
- Fe_D_CONC_BOTTLE::bnuivj
- PHOSPHATE_D_CONC_BOTTLE::lzvdkt
- CTDTMP_UP_T_VALUE_SENSOR::anjcri
- CTDSAL_UP_D_CONC_SENSOR::epwqn2

- Imported original file "BAIT_Bottle_Data_TM_CTD.xlsx" into the BCO-DMO system.
- Renamed fields to comply with BCO-DMO naming conventions.
- Created separate flag columns for NO3_NO2, PO43, and Si to indicate BDL and ND.
- Removed "BDL" and "ND" from data columns. Missing data are empty/blank in the final CSV file (quality flags of 5 = BDL and 4 = ND).
- Created date-time column in ISO 8601 format.
- Saved the final file as "937302_v1_bait_ctd_bottle_data.csv".

NSF and NERC Award Abstract:
Iron is an essential nutrient for the growth of phytoplankton in the oceans. As such, iron plays key roles in regulating marine primary production and the cycling of carbon. It is thus important that models of ocean biology and chemistry consider iron, in order to explore past, present and future variations in marine productivity and the role of the ocean in the global carbon cycle. In this joint project involving researchers in the U.S. and the U.K., supported by both NSF and the Natural Environment Research Council (U.K.), field data from the Bermuda Atlantic Time-series Study (BATS) region will be combined with an established, state-of-the-art ocean biogeochemical model. By leveraging the known seasonal-scale physical, chemical and biological changes in the BATS region, the oceanographic context provided by the BATS core data, and an existing model of the regional physical circulation, the proposed study will yield process-related information that is of general applicability to the open ocean. In particular, the proposed research will focus on understanding the atmospheric input, biological uptake, regeneration and scavenging removal of dissolved iron in the oceanic water column, which have emerged as major uncertainties in the ocean iron cycle. The project will include significant educational and training contributions at the K-12, undergraduate, graduate and postdoctoral levels, as well as public outreach efforts that aim to explain the research and its importance.

The ability of ocean models to simulate iron remains crude, owing to an insufficient understanding of the mechanisms that drive variability in dissolved iron, particularly the involvement of iron-binding ligands, colloids and particles in the surface input, biological uptake, regeneration and scavenging of dissolved iron in the upper ocean. Basin-scale data produced by the GEOTRACES program provide an important resource for testing and improving models and, by extension, our mechanistic understanding of the ocean iron cycle. However such data provide only quasi-synoptic 'snapshots', which limits their utility in isolating and identifying the processes that control dissolved iron in the upper ocean. The proposed research aims to provide mechanistic insight into these governing processes by combining time-series data from the BATS region with numerical modeling experiments. Specifically, seasonally resolved data on the vertical (upper 2,000 meters) and lateral (tens of kilometers) distributions of particulate, dissolved, colloidal, soluble and ligand-bound iron species will be obtained from the chemical analysis of water column samples collected during five cruises, spanning a full annual cycle, shared with the monthly BATS program cruises. These data, along with ancillary data from the BATS program, will be used to test and inform numerical modeling experiments, and thus derive an improved understanding of the mechanisms that control the distribution and dynamics of dissolved iron in the oceanic water column.

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.

This is a project jointly funded by the National Science Foundation’s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK). 

GEOTRACES is a SCOR sponsored program; and funding for program infrastructure development is provided by the U.S. National Science Foundation.

GEOTRACES gained momentum following a special symposium, S02: Biogeochemical cycling of trace elements and isotopes in the ocean and applications to constrain contemporary marine processes (GEOSECS II), at a 2003 Goldschmidt meeting convened in Japan. The GEOSECS II acronym referred to the Geochemical Ocean Section Studies To determine full water column distributions of selected trace elements and isotopes, including their concentration, chemical speciation, and physical form, along a sufficient number of sections in each ocean basin to establish the principal relationships between these distributions and with more traditional hydrographic parameters;

* To evaluate the sources, sinks, and internal cycling of these species and thereby characterize more completely the physical, chemical and biological processes regulating their distributions, and the sensitivity of these processes to global change; and

* To understand the processes that control the concentrations of geochemical species used for proxies of the past environment, both in the water column and in the substrates that reflect the water column.

GEOTRACES will be global in scope, consisting of ocean sections complemented by regional process studies. Sections and process studies will combine fieldwork, laboratory experiments and modelling. Beyond realizing the scientific objectives identified above, a natural outcome of this work will be to build a community of marine scientists who understand the processes regulating trace element cycles sufficiently well to exploit this knowledge reliably in future interdisciplinary studies.

Expand "Projects" below for information about and data resulting from individual US GEOTRACES research projects.