Table of Contents

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

Nine sediment cores were collected from three different sites in Clayoquot Sound, Vancouver Island, Canada in October 2023. One core was used for porewater sampling; this core was sampled immediately with Rhizon samplers. (See "Related Datasets" for the porewater data.) A second core was extruded under argon for geochemical measurements. 1 milliliter (mL) of sediment was added to a cryovial and frozen at -20 degrees Celsius (°C) for future DNA extraction. 5 mL of sediment was added to an exetainer containing 5 mL of 1 N NaOH to measure sediment methane concentrations. The remaining sediment from each extruded interval was added immediately to falcon tubes containing 10 mL of 20% zinc acetate to precipitate sulfides and halt microbial activity. A third archive core was immediately frozen at -20°C.

To determine bulk elemental concentrations (organic C/N/S) of sediments, 1 N HCl was added to ~100 milligrams (mg) of sediment to remove carbonate minerals. To isolate major carbon and sulfur pools, ~1 gram (g) of sediment (preserved in zinc acetate) was subjected to a strong acid hydrolysis (6 N HCl, 60°C, 2 hours) under N₂ to isolate acid-volatile sulfur (AVS; i.e., iron monosulfides). AVS was bubbled into a 5% zinc acetate solution and precipitated as zinc sulfide. Residual solid was rinsed with MQ, freeze dried, and subjected to two sequential microwave extractions (MARS-6, CEM, 70°C, 15 minutes) in a 9:1 dichloromethane: methanol solution to remove lipids and elemental S (Raven et al. 2016). Solvent-extracted solids were dried and underwent a chromium (II) chloride reduction (1:1 chromium (II) chloride: 6 N HCl, 60°C, 2 h) under N₂ to isolate chromium reducible sulfur (CRS; pyrite) (Canfield et al. 1986). CRS was bubbled into a zinc acetate solution and precipitated as zinc sulfide. The residual following CRS extraction was rinsed with MQ water, freeze dried, and is functionally defined as proto-kerogen (hydrolysis-resistant OM) (Burdige 2007; Raven et al. 2016).

De-carbonated bulk sediment samples and proto-kerogen samples were analyzed on an Elementar vario ISOTOPE select elemental analyzer interfaced to a Nu Horizon isotope ratio mass spectrometer to measure organic C/N/S and δ13C. AVS and CRS (precipitated as zinc sulfide) were oxidized to sulfate using 30% H₂O₂. Their concentrations were determined via ion chromatography (Metrohm 930 Compact IC Flex).

Samples analyzed in this study were collected within Ahousaht Territory, on the west coast of Vancouver Island, British Columbia. We respectfully acknowledge the Ahousaht Nation and the Maaqutusiis Hahoulthee Stewardship Society for their stewardship of these lands and for the opportunity to conduct research within their territory.

Organic C/N/S concentrations were calculated with a sulfanilamide standard curve (0.5 – 25 micromoles (µmole) N, 1.5 – 75 µmole C, 0.25 – 12 µmole S). Sample δ13C values were calibrated using carbon isotope standards USGS-61 (35.05‰), 62 (-14.79‰), and 63 (1.17‰) run in triplicate and are reported relative to Vienna Pee Dee Belemnite. Sulfate concentrations were calibrated using a sulfate standard curve (0.1 – 100 parts per million (ppm)). Fe(II) concentrations were calibrated using a Fe(II) standard curve (0 – 80 µM).

- Imported original file "20251007_FJ_sediments.csv" into the BCO-DMO system.
- Converted the date field to YYYY-MM-DD format.
- Saved the final file as "992723_v1_sediment_geochemistry.csv".

NSF Award Abstract:

CAREER: Particle-Hosted Sulfur Cycling and Organic Matter Burial in Oxygen Deficient Zones

Areas of the ocean without dissolved oxygen are called anoxic zones. These environments are increasing due to human activities and climate change. Large amounts of organic carbon are buried in sediments below anoxic zones. However, we do not fully understand why organic carbon is preserved in these zones. This project seeks to understand a newly discovered process that may contribute to carbon preservation in anoxic zones. The process is called organic matter sulfurization. Through this process, organic matter is transformed and effectively ?pickled? by reacting with sulfide. Rapid sulfurization reactions were identified for the first time in sinking marine particles and may have larger effect on carbon burial in sediments than previously thought. This project will be the first to provide measurements of the scale and significance of rapid organic matter sulfurization in modern anoxic zones. This project includes field and laboratory studies. The research will involve a team of students, including a graduate student and six undergraduates, who will be supported through a peer mentorship program. Undergraduate researchers will be recruited from the inaugural class of a newly developed Practical Research Skills course (Earth 101A) at the University of California Santa Barbara. It seeks to help undergraduates develop critical thinking and observational skills that have broad applicability. This project will launch a self-sustaining and vigorous research program in marine biogeochemistry, heavily invested in undergraduate research education, with impacts that will outlast its five-year duration.

The overarching research goal of this project is to assess the contribution of sulfurization reactions to organic carbon preservation in anoxic environments. After constructing and testing a set of customized particle traps, an expedition will be conducted to the marine anoxic zone off the coast of Mexico. Sinking particles, suspended materials, and surface sediments will be collected at three sites on the Mexican shelf and slope, that have generally high local productivity and gradients in bottom-water oxygen concentration. In the field, the rates and isotopic fractionation of microbial sulfate reduction and organic sulfur formation will be measured with stable and radioactive isotope tracers. Subsequently, organic sulfur sources from both natural samples and laboratory experiments will be characterized using mass spectrometry, X-ray absorption spectroscopy, and other geochemical techniques. Together, the results of this work will identify the timing and location of organic matter sulfurization in this environment, which have substantial implications for both modeling marine carbon fluxes and interpreting the geologic record. This study will provide the first quantitative estimates of the scale of organic matter sulfurization in anoxic marine zones, its contribution to sedimentary carbon burial, and its sensitivities to environmental change. Simultaneously, this project will improve the Earth Science undergraduate curriculum at the University of California Santa Barbara through the development of a clear, supportive, and accessible mechanism for including students in research.

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.