Table of Contents

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

Porewater samples from gravity cores were collected as described in Komada et al. (2016) Geochim. Cosmochim. Acta, 176:259-278. Briefly, sediment cores were sectioned within hours of retrieval, then centrifuged, filtered (0.2 micron pore size). Porewater samples from multicores were extracted using Rhizon samplers (Seeberg-Elverfeldt et al., Limnol. Oceanogr. Meth., 8:361-371, 2005) to prevent contamination from squashed benthic macrofauna during centrifugation. Samples from multicores (MC) were retrieved using Rhizon samplers (5 cm, 0.15 micron pore size). Samples from BB gravity cores were collected by centrifugation, then filtered through 0.2 miron filters. Samples were immediately poisoned with HgCl2 and flame-sealed under a stream of high-purity nitrogen gas and refrigerated until analysis. 

Blank samples: MQ_blank samples = UV-irradiated MQ water collected on the ship in parallel with porewater samples; Rhizon_blank samples = UV-irradiated MQ water collected on in the laboratory after passing it through a Rhizon sampler.

1H NMR spectra were acquired in 5-mm O.D. thin-wall precision NMR tube (Bel-Art Wilmad part #528-PP-7-5) in 5% D2O (Sigma Aldrich part #151882) using a Bruker Avance NEO 500 MHz instrument with Prodigy cryoprobe using W5-WATERGATE solvent suppression method (Lam and Simpson, Analyst, 133:263-269, 2008). 

NMR spectra were normalized by the total area under the spectra after removing the residual water peak (4.2-5.0 ppm).

* Converted original data that was in wide format to long format. Both files are part of this dataset.
* Added sampling latitude and logitude to dataset
* Adjusted parameter names to comply with database requirements (no periods, spaces or special characters)

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.