Table of Contents

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

Pore-water sampling. Pore-waters were extracted from the upper N 30 cm of sediments along an Equatorial Pacific transect at 14O”W, from 12% to 9”N, at a water depth of approximately 4300 m (JGOFS-EqPac, Leg TTO13, November 1993); sample locations and water depths are listed in Table 1. Sediments were collected using a multi-corer. All cores had a well-preserved sediment-water interface with an occasional fluff of phyto-detritus, overlain by clear bottom seawater. Thus, sediment disturbance seems to have been minimal during the coring and recovery operations. Sub-cores were transferred within minutes of arrival on board into a cold room of 2”C, where they were sectioned into 0.5, 1 and 2 cm intervals in a nitrogen atmosphere glove bag and centrifuged at 700010,000 rpm. The pore-waters obtained were passed through pre-washed Nucleopore 0.45 km filters in a nitrogen atmosphere, acidified to a pH of 2 with distilled HNO3, and stored in acid-cleaned polypropylene bottles at 2°C. The pore-water sampling procedure was usually completed within less than 24 h of core recovery. Two cores from each latitude were processed in order to identify spatial variability. All the equipment used for sample processing was thoroughly pre-cleaned with 8 N HNO3, in order to reduce the blank.

Pore fluid sampling methods: Paytan et al., 1996 (see related publications). 

Barite and seawater sampling. Dissolved seawater samples were collected on the ProteOMZ FK150116 expedition (Jan-Feb 2016) using a 12-bottle trace metal clean rosette equipped with 8 L X-Niskin bottles (Ocean Test Equipment), a titanium frame, and a Kevlar cable, as described in (Cutter and Bruland 2012). Seawater from the Go-Flo bottles was subsampled in a trace metal clean plastic "bubble" equipped with HEPA filters providing positive air pressure. Dissolved Ba subsamples were filtered using a 142 mm polycarbonate plastic sandwich filter (Geotech Environmental Equipment) equipped with a 0.2 um Supor membrane filter (Pall Corporation) and stored until analysis in the laboratory in a 60 mL HDPE bottle (Nalgene) that had been soaked for ~1 week in Citranox, an acidic detergent, rinsed with Milli-Q water (Millipore), soaked for ~2 weeks in 10% trace metal grade HCl (Optima), and rinsed with lightly acidic Milli-Q water (<0.1% HCl). Samples were stored at 4⁰C.

Barite processing. Barite samples were dissolved through an alkaline dissolution in perfluoroalkane vials by addition of 1 M Na2CO3 solution to form (Ba,Ca)CO3 as in Breit et al. (1985). The Na2CO3 solution was added to achieve BaSO4:Na2CO3 of 1:10 by mass, then 18.2 M water was added such that there was 10 mg of BaSO4 per 2 mL of solution. Samples were then sonicated for 60 minutes at room temperature and then heated to 80◦C for ≥16 h. After cooling, the fluid was decanted and two further rounds of Na2CO3 addition, sonication, heating, and decantation were performed. Samples were rinsed with 18.2 M water and the remaining solid, BaCO3, dissolved with 2 M HCl. An aliquot of this solution was equilibrated with a 135Ba–136Ba double spike of known concentration to achieve a spike- to sample-derived [Ba] ratio of between 1–2 and reconstituted in 250 μL of 2 M HCl ready for ion-exchange chromatography.

Porewater and seawater processing. Porewater and seawater samples were prepared for Ba isotope analysis following the procedure outlined in Bates et al. (2017).

Briefly, dissolved samples were equilibrated with the double spike and then co-precipitated into (Ba,Ca)CO3 by drop-wise addition of 1 M Na2CO3. The precipitate was then dissolved in 250 μL of 2 M HCl for chromatography. Barium was purified from matrix elements by passing all samples twice through 500 μL of AG 50W-X8 (200–400 mesh) cation-exchange resin (Bio-Rad), following the protocol described by Horner et al. (2015).

Isotope analysis. Full barium isotope measurement methods can be found in: Middleton et al., 2023. (see related publications).

Purified Ba was analyzed for Ba isotopes using a ThermoFinnigan Neptune multi-collector inductively coupled plasma mass spectrometer in the WHOI Plasma Facility. Isotope compositions were calculated using the three-dimensional geometric interpretation of the double-spike problem (Siebert et al., 2001) with additional processing for isobaric corrections (136Xe and 136Ce on 136Ba, 138Ce and 138La on 138Ba; Horner et al., 2015). Barium isotope compositions were calculated relative to NIST by standard-sample bracketing. Four procedural blanks were found to range from 305 to 489 pg, below the long-term average NIRVANA Labs procedural blank (692 pg). A further four analytical blanks were found to range from 14 to 301 pg. The contribution of the highest blank to the sample with the lowest [Ba] was < 3%. Given the low blank contribution and poor constraints on the true Ba isotope blank value, no blank correction was applied. Barium isotope compositions are reported as deviations in the 138Ba/134Ba ratio in a sample relative to the NIST SRM 3104a standard, hereafter ‘NIST’: δ138Ba( ) = [(138Ba/134Ba)sample/(138Ba/134Ba)NIST−1]×1000. Uncertainties are reported as either a long-term measurement of uncertainty (±2 SD about the mean; ± 0.03 , Horner et al., 2015) or pooled 2 SE from n sample analyses, whichever was greater. Accuracy of isotope measurements was monitored by processing two internal reference materials alongside samples: the Alfa Aesar BaSO4 powder and GEOTRACES SAFe D1 (northeast Pacific seawater; 1,000 m). The BaSO4 and SAFe D1 possessed δ138Ba = −0.02 ± 0.03 and +0.33 ± 0.04 , in agreement with previous measurements of −0.04 ± 0.07 (n = 7, ±2SE; T.J. Horner pers. comm.) and +0.31 ± 0.03 (Cao et al., 2020; Geyman et al., 2019; Hsieh and Henderson, 2017), respectively.

CURATION ACTIONS PERFORMED ON DATA
approved by submitter

* Two Excel source files, 2022-11-17_JGOFS_manuscript_DataTables_BCODMO.xlsx and 2022-11-17_ProteOMZ_manuscript_DataTables_BCODMO.xlsx
* blanks, nd, and NaN were set as missing-value markers
* The two source tables were concatenated into a single table, following fields were merged: Core_id & Stn_id, Ba_conc_err & Ba_conc_2SE, 138Ba_iso_err & 138Ba_iso_2SE, depth_water_m & Depth_m
* Sample_type was standardized so that records with Cruise_id = FK160115 were classified as Seawater; existing Sample_type values were retained for all other records.
* fields were renamed: 138Ba_iso → Ba138_iso, 138Ba_iso_err → Ba138_iso_err, , Core_id (from Stn_id) → Sample_id,Long → Lon, depth_core → Depth_core, and depth_water_m → Depth_water_m.
* The concatenated table was renamed 1005542_v1_bariumisotopes.

CURATION ACTIONS PERFORMED ON METADATA
approved by submitter

* Merged metadata entries from 2 submission
* Added standardized instruments

ISSUES POTENTIALLY IMPACTING REUSE

* no measurement specific sampling date provided

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.