Table of Contents

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

Field sampling methods:
Sediment cores were collected using a gravity corer and a multicorer on both cruises. Following recovery, the gravity cores were secured horizontally on the ship's deck and sampled from the bottom of the core upwards. This was done by sequentially removing 10-centimeter (cm) sediment intervals by cutting the core liner using a pipe cutter. Freshly exposed sediment was immediately subsampled using 3- to 60-milliliter (mL) push corers made of plastic syringes with the tips removed. All subcores were immediately transferred to an N2 filled glove bag in a refrigerated van for further processing. Multi cores were transferred to a refrigerated van immediately upon recovery, and within 12 hours were either sampled using pre-cleaned Rhizon samplers (Seeberg-Elverfeldt et al., 2005) or extruded and sectioned in an N2 atmosphere at intervals of 0.5 to 2 cm depth over the depth of the core (generally 30 to 40 cm total length).

While it is possible to recover intact sediment-water interfaces using multi-corers, loss of surface sediments is typical during gravity coring, making it impossible to directly quantify absolute depths below the sediment-water interface in a gravity core. We therefore determined absolute depths of sediment sample intervals in gravity cores by aligning DIC, SO42-, NH4+, and porosity gravity core profiles to multicore profiles from the same site (Berelson et al., 2005; Iversen and Jørgensen, 1985; Komada et al., 2016).

Sediment aliquots from both gravity cores and sectioned multi cores were centrifuged at 6 degrees Celsius (°C) in polycarbonate tubes, and the supernatant was collected into all-polypropylene syringes with stainless steel needles. Rhizon samples were also collected in all poly-propylene syringes. All pore water samples were then filtered through disposable 0.2 micrometer (µm) nylon filters with 0.7 µm GF/F pre-filters (Whatman 6870-2502). The first 3 mL were discarded. To minimize the DOC blank, 100 mL of UV-irradiated deionized water (DIWUV) were pushed through each disposable filter prior to use.

Pore water samples for DIC concentration were placed in 2-mL serum vials without headspace, immediately crimp sealed, and refrigerated until analysis (Burdige and Homstead, 1994). Alkalinity samples were collected in 3-mL plastic syringes, sealed with 3-way stopcocks, and titrated on-board the ship within 24 hours. Titrated alkalinity samples were placed in snap cap vials and later used for sulfate and ammonium determinations.

Pore water samples for DOC concentration were acidified to pH < 2 with 6 N trace metal grade HCl and flame-sealed in pre-combusted glass ampules under a stream of UHP N2 gas and refrigerated.

Pore water samples for total dissolved sulfide (∑H2S = [H2S] + [HS-] + [S2-]) analysis were fixed onboard ship by adding pore water to an N2-degassed solution containing 4 mL of 5 millimolar (mM) ZnCl2 and and 4 mL of 10 mM NaOH (Ingvorsen and Jørgensen, 1979) in a 10 mL serum bottle. At the basic pH of this "fixing" solution, all dissolved inorganic sulfide precipitates out as ZnS. The headspace was then degassed with N2 and the bottle was crimp sealed with plug-style stoppers and refrigerated. In SBB pore water samples near the sediment surface (upper 10 cm) where sulfide levels are low, 1 mL of pore water was added to the fixing solution, whereas for deeper samples (with higher sulfide levels) 0.1 mL pore water was added to the fixing solution. In station D and K pore water samples, 1-2 mL pore water was added to the fixing solution. ∑H2S was not determined in Cat pore water samples.

Bottom-water samples were collected from 10 meters (m) above the seafloor with a Go Flo bottle. All tools and parts used in all sampling were first cleaned with household dish soap, then acid rinsed (exclusive of metal parts). Plasticware was air dried.

Analytical methods:
Alkalinity samples were titrated on-board the ship by automated Gran titration (Burdige et al., 2010). pH values listed here are the initial pH values from the titrations and are expressed on the NBS scale. Concentrations of DIC and ammonium (SBB and Cat samples) were analyzed by flow injection analysis (Hall and Aller, 1992; Lustwerk and Burdige, 1995). Ammonium (stations D and K) was determined by the fluorometric technique of Holmes et al. (1999). Sulfate was determined by ion chromatography with conductivity detection (Komada et al., 2016). ∑H2S was determined spectrophotometrically using the methylene blue technique (Cline, 1969). All reagents were added directly to the serum bottle containing the ZnS suspension (see the section above for details).

Concentrations of DOC were determined by high-temperature combustion using a Shimadzu TOC-V total carbon analyzer (Burdige and Gardner, 1998). DOC consensus reference materials (D. Hansell, RSMAS) were run along with samples, and measured values agreed to within <10% with the reported consensus values.

- Imported original file "pore water data.txt" into the BCO-DMO system.
- Flagged "nd" as a missing data value (missing data are empty/blank in the final csv file).
- Converted Date column to YYYY-mm-dd format.
- Added cruise ID column.
- Saved final file as "959247_v1_pore_water.csv".

NSF Award Abstract:
Dissolved organic matter (DOM) in the ocean is one of the largest carbon reservoirs on Earth. Much of this DOM is highly resistant to degradation (refractory) and aged, but the nature and reasons behind the accumulation of refractory DOM in the ocean is one of the unresolved mysteries of the marine carbon cycle. While marine sediments have been shown to be a globally important source of DOM to the ocean, the connection between sediment DOM dynamics and the oceanic DOM cycle remains elusive, because information is lacking on the molecular composition and reactivity of pore water DOM. To fill this knowledge gap, this project will address the question of how refractory DOM is produced in sediments and the fate of benthic DOM in the water column. The research will focus on the relationship between protein/peptide dynamics and sediment DOM cycling, examining peptide deamination as an important pathway for the production of refractory and 14C-depleted DOM in continental margin sediments. These objectives will be met through a combination of geochemical profiling of sediment cores collected across a range of redox conditions, and long-term sediment incubation studies conducted under controlled laboratory conditions. At the heart of this proposed work is structural elucidation and quantification of intact and deaminated peptides in pore-water DOM using state-of-the-art analytical techniques. The study will help better understand how the present-day carbon cycle operates, as well as how it may respond in the future. The proposed work will integrate research and education using several approaches. All PIs routinely integrate their research into their classes, which range from introductory-undergraduate to advanced-graduate courses and will continue to do so here. All three PIs are also committed to engaging women and underrepresented minority students.

Marine sediments are a globally important source of dissolved organic matter (DOM) to the ocean. However, the connection between sediment DOM dynamics and the oceanic DOM cycle remains elusive because information about the molecular composition and reactivity of pore water DOM is lacking. To help fill this knowledge gap, this project will address the question of how refractory DOM is produced in sediments and the fate of the benthic DOM flux in the water column. The proposed study explores a novel and potentially transformative idea that deamination of peptides in sediments is a source of refractory and 14C-depleted DOM in seawater. This idea is consistent not only with the fact that the majority of seawater dissolved organic nitrogen occurs in amide form, but also with recent reports about the widespread occurrence of nitrogen-bearing formulas in deep-sea refractory DOM. The central hypothesis will be tested through a unique blend of bottom-up (molecular level DOM analyses) and top-down (bulk-level elemental and isotopic analyses, and numerical modeling) approaches. This work will involve a combination of geochemical profiling of sediment cores collected across a range of redox conditions, and long-term sediment incubation studies conducted under controlled laboratory conditions. At the heart of the proposed work is structural elucidation and quantification of intact and deaminated peptides in pore-water DOM using a state-of-the-art liquid chromatography-mass spectrometry system (ultra-high performance liquid chromatography coupled to an Orbitrap Fusion Tribrid Mass Spectrometer), which is expected to provide an unprecedented wealth of molecular-level information about pore water DOM. The proposed work will lead to an improved mechanistic understanding of organic matter decomposition and benthic DOM cycling and shed light on the connections between the modern-day oceanic and sedimentary carbon and nitrogen cycles as they relate to the formation of refractory DOM.

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.