Table of Contents

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

Seawater samples were obtained from three GO-SHIP Repeat Hydrography transects to measure stable carbon isotopic composition of solid-phase extracted dissolved organic matter (SPE-DOC δ¹³C). Transect P16N (151°W) sampled in the year 2015, P18 (103-110°W) in 2016 and 2017, and transect I07N (50-70°E) in 2018 aboard the NOAA Ship Ronald H. Brown (see Figure 1), at or within 1 station of an associated total DOC sample (Druffel et al., 2019, 2021, 2023). “Surface” and “deep” samples were collected at 0-200 meters and 2000-4000 meters, respectively. Due to the integration of seawater among different stations and depth, we report the weighted average depth which is the weighted mean that incorporates the relative amount of each water depth into the final value. (See Supplemental Files section for the equation). 

 Due to excess water availability, two samples (called "seawater duplicates or SD) were collected from P18 stations 77-79 (in deep water), and 168 (in surface water). For seawater samples from P18 and IO7N, solid phase extraction (SPE) was performed at sea using PPL cartridges (Bond Elut-PPL, 1 gm 6 ml, Part No. 12255002) according to Dittmar et al. (2008) and stored in the dark at 4°C until elution at UC Irvine. Seawater samples from the P16N cruise were processed after four years of freezing. Samples were then acidified to pH 2 with sulfuric acid (ACS grade, Lot #160,128) and extracted onto PPL cartridges. Before elution, PPL cartridges were dried under a steady stream of ultra-high purity N₂ gas for 30 min to remove residual MilliQ water (3 ppb DOC). SPE-DOC was eluted with LC/MS grade methanol following established methods (Dittmar et al., 2008). However, the elution volume of methanol was increased to 32 mL to increase yield of SPE-DOC (Lewis et al., 2020). SPE-DOC was eluted into pre-weighed and pre-combusted (540°C/2h) 50 mL centrifuge vials (VWR product #89091-460), and weighed after elution to determine the exact volume. 

 Splits were dried in a centrifugal evaporator with a −60°C chiller trap (Savant SpeedVac SC200) for a minimum of 12 hours. Pre-baked cupric oxide and silver wire were added, and the outside of these quartz tubes were cleaned with acetone, dried, and placed inside larger 9 mm diameter, 20 cm long quartz vials. These “double tube” samples were sealed under vacuum and combusted at 850°C for two hours. Sample CO₂ was extracted cryogenically on a vacuum line and quantified manometrically.

Stable carbon isotopic measurements (δ¹³C) were made using a Gas Bench II and Thermo Electron Delta Plus mass spectrometer, and corrected using calibrated isotopic standards (NIST NBS-19). Measurements are reported as standard permille (‰) relative to V-PDB (Vienna Pee-Dee Belemnite) scale. Duplicate and triplicates taken from certain SPE-DOC extracts from all three cruises show our SPE-DOC δ¹³C measurement precision averages better than 0.2‰ providing confidence that the variability seen throughout different ocean regions is real.

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This work was supported by the National Science Foundation Chemical Oceanography Program (OCE-1458941 and OCE-1951073 to E.R.M.D.), the U.S. American Chemical Society Petroleum Research Fund New Directions Grant (55430-ND2 to E.R.M.D. and B.D.W.), the Fred Kavli Foundation, and the Keck Carbon Cycle AMS Laboratory. A portion of this work was funded by the Natural Sciences and Engineering Research Council (NSERC) of Canada through a Discovery Grant, Accelerator and Launch Supplements (RGPIN-2020-06501, RGPAS-2020-00071, DGECR-202000256; to B.D.W.), the New Frontiers in Research Fund (NFRFE-2019-00794 to B.D.W.) and the Canada Research Chairs program (to B.D.W.). A portion of this work was also funded by the New Zealand Ministry of Business, Innovation and Employment (MBIE) through the Global Change through Time programme (Strategic Science Investment Fund, contract C05X1702)

δ¹³C values are blank-corrected for a known amount of extraneous carbon previously reported (Lewis et al., 2020). This is done using a mass-balance calculation. The included data includes the raw and corrected values.  

δ13C measurements are reported as standard permille (‰) relative to V-PDB (Vienna Pee-Dee Belemnite) scale. Additional corrections are required for extraneous carbon added during sample workup. The blank correction procedure is reported in Lewis et al. (2020).   

The code used to analyze the data and produce figures can be found in Lewis (2024) GitHub repo, and in the Supplemental Files section below.  

- Imported data from source file "OPEN_ACCESS_DATA_FILE_BCODMO.xlsx"
- Created new columns for Sample_note and Cruise_ID
- Created a date column based on the EXPOCODE
- Modified parameter (column) names to conform with BCO-DMO naming conventions. The only allowed characters are A-Z,a-z,0-9, and underscores. No spaces, hyphens, commas, parentheses, or Greek letters.

NSF Award Abstract:
Controls on the Aging of Marine Dissolved Organic Carbon

Most of the organic carbon in ocean water is in the dissolved form. Surprisingly, the age of this dissolved organic carbon is thousands of years old, even though it is thought to form during photosynthesis in the surface ocean. One explanation for the age of this carbon is the amount of time that it takes for carbon to circulate through the ocean. Investigators at the University of California Irvine (UCI) will investigate the aging of dissolved organic carbon in the Pacific, Southern and Indian oceans using C-14 isotopes. This work is important for knowing how carbon produced from human activities will be distributed on Earth in the future. This project will support the work of two graduate and two undergraduate students, providing hands-on experience that will prepare them for careers as scientists and educators. Both graduate students will be involved in a variety of educational activities. They will also help teach a short course on applications of C-14 in Ecology and Earth System Science for graduate students, technicians, postdocs and researchers during summer. UCI is a Hispanic-serving institution (27% of undergraduates identify as Hispanic), and 60% of students who attend UCI are first generation family representatives.

This study will examine the concentration, isotopic (14C, 13C) and molecular composition of dissolved organic carbon (DOC) in depth profiles from the Pacific, Southern and Indian Oceans. This information will help to determine the main controls on DOC cycling in the world’s oceans. The project will test the hypothesis that circulation is the primary control on DOC cycling in the deepest water (>3500 meters). The research will also investigate two alternative processes that could influence the age of DOC in deep water (2000-3000 meters): (1) dissolution of surface-derived particles and (2) input of ancient carbon from hydrothermal vents and flanks. Spectroscopic and spectrometric measurements designed to characterize a portion of the DOC will be performed on surface and deep water. Results will be incorporated into an inverse model of DOC cycling to determine the main processes controlling the DOC cycle in the ocean. DOC may serve as a sink for excess carbon dioxide produced from human activities and the size of the refractory DOC pool in the ocean could increase as circulation slows. Measuring the 14C age of DOC in the surface and deep ocean is important for understanding how the global carbon cycle will change as the Earth's climate shifts.

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.