Table of Contents

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

Porewater DIC samples 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), and preserved (poisoned then flame sealed under nitrogen gas). Porewater DOC samples were extracted in the same way from SBB sediments, as well as from gravity cores from all remaining stations (CAT, StaD, StaK). However, porewater DOC samples from multicores retrieved from CAT, StaD and StaK were extracted using Rhizon samplers (Seeberg-Elverfeldt et al., Limnol. Oceanogr. Meth., 8:361-371, 2005) to prevent DOC contamination from squashed benthic macrofauna during centrifugation. DOC samples for radiocarbon analysis were immediately frozen, or acidified to pH 2 with hydrochloric acid and loaded onto a PPL cartridge (Dittmar et al., Limnol Oceanogr. Meth., 6:230-235, 2008) and refrigerated.  Sediment samples were frozen immediately in polycarbonate centrifuge tubes. Bottom water samples were collected using acid-washed Go-Flo bottles. DOC samples were filtered (0.2 micron) and frozen. DIC samples were poisoned with HgCl2 and sealed in glass bottles.

Frozen porewater and bottom-water DOC were submitted to the Druffel Laboratory at UC Irvine for oxidation via UV irradiation (Beaupre et al., Limnol. Oceaongr. Meth., 5:174-184, 2007) followed by determination of 14C content via accelerator mass spectrometry (AMS) at the Keck Carbon Cycle AMS Laboratory. DOC samples loaded onto PPL cartridges were eluted in methanol into quartz tubes and processed via sealed-tube-combustion (STC) as described in Druffel et al. (1992) J. Geophys. Res., 97:15,639-15,659. CO2 thus recovered were graphitized (Xu et al., Nucl. Instr. Meth. Phys. Res. B, 259:320-329, 2007) and submitted to UC Irvine for AMS analysis. Porewater DIC samples were extracted via acidification under vacuum, purified cryogenically, and CO2 yield quantified manometrically as described in Komada et al. (2016) Geochim. Cosmochim. Acta, 176:259-278. CO2 samples were graphitized as described above and submitted to UC Irvine for AMS and IRMS (for 13C). Bottom-water DIC samples were submitted as is to NOSAMS for 14C analysis.

To determine POC, known mass of dried and homogenized sediment samples were acidified (Komada et al., Limnol. Oceanogr. Meth., 6:254-262, 2008) then processed via STC as described above. Total carbon and total nitrogen were determined on non-acidified samples using a Costech elemental analyzer.

All borosilicate glassware were soaped, acid rinsed, then ashed at 550 deg.C for 4 hours. All quartz glass and cupric oxide wires were ashed at 850 deg.C for 4 hours. All plastic-ware were soaped, acid rinsed, then dried under stream of HEPA-filtered air.

All isotope measurements were conducted at outside institutions.

All radiocarbon values from UC Irvine have been corrected for modern and dead carbon blanks according to Santos et al. (2007) Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 259: 293-302.

* Adjusted parameter names to comply with database requirements

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.