Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Curation Notes
  • Problem Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

These data correspond to the seawater and groundwater entries in Table 2 of Mayfield et al. (2024).

Samples were collected as part of the Red Sea Dust, Marine Particulates and Seawater Time Series program. Dissolved seawater samples were collected from vertical profiles at Station A in the Gulf of Aqaba using trace metal clean sampling procedures following GEOTRACES protocols. Seawater was collected using acid-cleaned, Teflon-coated GO-Flo bottles and transported to a clean laboratory within 1 to 2 hours. Samples were filtered through an acid-cleaned Acropak 500 cartridge filter (0.8/0.2 micrometer polyethersulfone), acidified with trace metal clean hydrochloric acid to pH less than or equal to 2, and stored refrigerated in acid-cleaned polypropylene vials prior to analysis. One coastal groundwater sample was collected from a shallow well near the shoreline at the Interuniversity Institute for Marine Sciences in Eilat and was processed for dissolved barium concentration and barium isotope analysis.

Barium isotope compositions are reported in delta notation (δ138Ba) relative to NIST SRM 3104a. Instrumental mass bias and isotope ratios were corrected using a double-spike technique. A spiked standard was analyzed every fifth sample, and sample values were normalized to bracketing standards. Analytical precision is reported as the greater of long-term reproducibility (plus or minus 0.03 per mil, 2 standard deviations) or the standard error of replicate analyses. Data processing and calculations were performed using MATLAB R2018a. Dissolved barium concentrations were determined using isotope dilution and were corrected for procedural blanks. In one batch of seawater samples, elevated blank levels required larger corrections (see Problems/Issues); replicate analyses confirmed that corrected concentrations and isotope compositions were consistent with samples processed under lower blank conditions.

- Loaded table "Dissolved Samples.xlsx" from Excel file and "nd" values as missing data
- Converted sample_collection_date column from string format "%m-%d-%y" to date type with output format "%Y-%m-%d"
- Renamed table dissolved_samples-1 to 1004832_v1_dissolvedbarium

NSF Award Abstract:
The biological cycling of carbon in the oceans entrains many other elements, some directly (like nutrients that are essential for life) and some indirectly, as they become chemically involved in the processes that are affecting carbon. One such element is barium (Ba). Particles of the mineral barite (barium sulfate) have been found to form in association with microbial consumption of organic material in the ocean’s “twilight zone.” These particles settle to the ocean floor, and their presence in sediments has been used to infer changes in the conditions in the ocean back in time. Both the amount of barite in sediments and the isotope composition of Ba in barite are potentially sensitive to processes occurring in the twilight zone. However, several long-standing questions remain about Ba cycling in the oceans, which complicates the interpretation of barium-based proxy records. Examples of remaining questions include how much barium enters the oceans at mid-ocean ridge hydrothermal sites, and what controls the precipitation and dissolution of barite in the water column. This project seeks to tackle these questions using new approaches, on three scheduled research expeditions in the Pacific and Southern Oceans. In doing so, this project will support the education, training, and career development of a graduate student, postdoctoral researcher, and junior investigator. Undergraduate students from underrepresented groups will be recruited to conduct complementary shore-based experiments.

This proposal seeks to answer four questions central to the utility of barium-based proxies in oceanography: What are the major inputs of new Ba to the ocean? What are their isotopic compositions? What controls the amount of pelagic barite precipitated during the remineralization of organic matter? What influences its isotopic composition? These questions will be addressed using a field-centric approach combining: in situ and shipboard tracer-incubation experiments, AUV-led adaptive sampling of Ba cycling ‘hotpots’, and section-based surveying of the surrounding oceanographic features. This multi-pronged approach will be used to investigate: the flux and isotopic composition of Ba released from the largest hydrothermal fields in the ocean, the Southern East Pacific Rise, with a focus on low-temperature venting; rates and signatures of pelagic barite precipitation associated with different phytoplankton assemblages in the Southern Ocean; and, the importance of environmental conditions, such as low ambient oxygen concentrations, in setting the efficiency of barite precipitation in the Eastern Tropical Pacific. The significance of each transformation will be assessed, which may lead to ruling out the importance of certain processes, or identifying new dependencies that could form the basis of new proxies.

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.