Table of Contents

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

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 Co 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 LDPE 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). To preserve the samples for future analysis after the cruise, all samples were filled entirely with no remaining headspace, stored with one oxygen-absorbing satchel (Mitsubishi Gas Chemical, model RP-3K) per 60 mL water sample, heat-sealed in plastic bags, and stored at 4⁰C.

Dissolved cobalt (dCo) samples were analyzed in Nov-Dec 2017 by cathodic stripping voltammetry (CSV) as originally described by (Saito and Moffett 2001) and modified by (Saito et al. 2010; Hawco et al. 2016). One portion of the samples (stations 1-10) were analyzed in the Saito laboratory in Woods Hole, MA, and the remaining samples (stations 11-14) were analyzed at sea on the CICLOPS NBP-1801 cruise in the trace metal plastic "bubble". This was done so that all of the samples could be run together using the same batch of DMG and EPPS reagents.

Dissolved Co was measured using a Metrohm 663 VA and uAutolabIII system equipped with a hanging mercury drop working electrode. All reagents were run through treated Chelex-100 resin columns (BioRad) to remove trace metal contaminates, except DMG which was purified by recrystallization. The Chelex was resin prepared as described in (Price et al. 1988/89) and reagents were purified as described in Saito et al., 2002. 0.2 um filtered water samples were UV-irradiated in acid-washed quartz tubes for one hour using a water-cooled UV irradiation system (Metrohm 705 UV Digestor) to destroy natural ligand-bound Co complexes. Then, 11 mL of sample seawater was aliquoted into 15 mL acid-washed polypropylene vials, and 100 uL of 0.1 M dimethyglyoxime (DMG, Sigma Aldrich) and 130 uL of 0.5 M N-(2-hydroxyethyl)piperazine-N-(3-propanesulfonic acid) (EPPS, Sigma Aldrich) buffer was added. The samples were then processed on an autosampler (Metrohm 858 Sample Processor), which added 8.5 mL of the sample solution and 1.5 mL of a 1.5 M NaNO₂ reagent (Merck) to a Teflon cup for electrochemical analysis. The mercury electrode performed a fast linear sweep from -1.4 V to -0.6 V at a rate of 5 V s⁻¹, which reduced the Co bound in the Co(DMG)₂ complex from Co(II) to Co(0) and produced a Co reduction peak at -1.15 V (Saito and Moffett 2001) with a height linearly proportional to the amount of dCo present in the sample. A standard addition curve was generated for each sample analyzed with 4 automated additions of a 25 pM CoCl₂ (Fisher Scientific) standard made fresh in for this sample batch.

Data Processing:
Peak heights were determined by NOVA 1.10 software. A linear regression of the standard addition peak heights allowed for the calculation of the initial amount of Co present in the sample, as described in (Saito and Moffett 2001). Triplicate technical replicates were run on every sample.

Quality Flags:
The dataset includes quality assurance flags described in the GEOTRACES Quality Flag Policy, which is available at https://www.geotraces.org/geotraces-quality-flag-policy/. Some dCo values reported are suspected misfires and are accordingly labeled with a QC flag of 3.
Brief flag descriptions:
0 = no quality control;
1 = good value;
2 = probably good value;
3 = probably bad value;
4 = bad value;
5 = changed value;
6 = value below detection;
7 = value in excess;
8 = interpolated value;
9 = missing value.

BCO-DMO Processing:
- renamed fields;
- added fields for date-time in ISO8601 format;
- replaced 'NaN' with 'nd' as the missing data identifier;
- rounded Cobalt values as specified by data submitter;
- 2022-09-08: made a correction to the Acquisition Description section of the metadata. The filter size used on dissolved Co subsamples was 0.2 um (not 0.4 um as previously stated).

From Schmidt Ocean Institute's ProteOMZ Project page:

Rising temperatures, ocean acidification, and overfishing have now gained widespread notoriety as human-caused phenomena that are changing our seas. In recent years, scientists have increasingly recognized that there is yet another ingredient in that deleterious mix: a process called deoxygenation that results in less oxygen available in our seas.

Large-scale ocean circulation naturally results in low-oxygen areas of the ocean called oxygen deficient zones (ODZs). The cycling of carbon and nutrients – the foundation of marine life, called biogeochemistry – is fundamentally different in ODZs than in oxygen-rich areas. Because researchers think deoxygenation will greatly expand the total area of ODZs over the next 100 years, studying how these areas function now is important in predicting and understanding the oceans of the future. This first expedition of 2016 led by Dr. Mak Saito from the Woods Hole Oceanographic Institution (WHOI) along with scientists from University of Maryland Center for Environmental Science, University of California Santa Cruz, and University of Washington aimed to do just that, investigate ODZs.

During the 28 day voyage named “ProteOMZ,” researchers aboard R/V Falkor traveled from Honolulu, Hawaii to Tahiti to describe the biogeochemical processes that occur within this particular swath of the ocean’s ODZs. By doing so, they contributed to our greater understanding of ODZs, gathered a database of baseline measurements to which future measurements can be compared, and established a new methodology that could be used in future research on these expanding ODZs.