A Caltech Library Service

Organic Matter Sulfurization in the Modern Ocean


Raven, Morgan Reed (2016) Organic Matter Sulfurization in the Modern Ocean. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z91Z42B0.


Only a tiny fraction of the carbon fixed by primary producers in the surface ocean is preserved in sediments, but this organic matter (OM) burial is one of the main processes linking the short and long-term carbon cycles, giving it important roles in global biogeochemistry. OM-rich deposits often contain abundant organic S (OS), and sulfur incorporation is thought to make OM less available for heterotrophs and more likely to be preserved. Still, we have few constraints on the significance of sulfurization for OM burial in the modern ocean, and fewer on how that flux might have differed in the past. This thesis applies a new generation of analytical tools for S-isotope analysis to investigate the timescales and mechanisms of OM sulfurization in the modern ocean. By measuring the δ34S values of minor S phases and individual S-bearing organic compounds as well as major sedimentary phases, we are able to make progress on long-standing questions about the distribution of S isotopes among organic and inorganic S phases in sediments.

Chapters 2 and 3 focus on Cariaco Basin, where a large proportion of the OS in sediments appears to derive from OM sulfurization in particles sinking through the water column. Rapid sulfurization likely involves polysulfides and is associated with high primary productivity and OM export. In the sediments, low-molecular-weight organosulfur compounds accumulate over longer timescales and have low and distinctive δ34S values. Chapter 4 presents records from Santa Barbara Basin, where OS appears to be exchanging with less abundant porewater sulfide and controlling its δ34S value. As in many environments, pyrite in these sediments is more 34S-depleted than either OS or sulfide. We attribute this pattern to pyrite formation within sulfide-generating microenvironments prior to equilibration between OS and sulfide in porewater. Chapter 5 tests the feasibility of the proposed OS–sulfide exchange and confirms that sulfide δ34S can reflect equilibrium with natural OM. We also find evidence that sulfurization of thiols may involve an interim polysulfide that includes the thiol S atom, providing a mechanism to mix biogenic S into proto-kerogen and potentially helping explain differences between the global pyrite and OS S-isotope records.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Biogeochemical cycles; sediments; organic sulfur; pyrite; organic matter; diagenesis
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Sessions, Alex L.
Thesis Committee:
  • Adkins, Jess F. (chair)
  • Sessions, Alex L.
  • Fischer, Woodward W.
  • Lyons, Timothy W.
Defense Date:6 May 2016
Funding AgencyGrant Number
National Science FoundationEAR-1024919
National Science FoundationOCE-1258991
National Science FoundationOCE-1529120
Gordon and Betty Moore FoundationGBMF#3306
National Science FoundationOCE-1436566
Record Number:CaltechTHESIS:05262016-125832967
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2 adapted for ch. 4
Raven, Morgan Reed0000-0003-4953-9966
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9766
Deposited By: Morgan Raven
Deposited On:31 May 2016 19:00
Last Modified:04 Oct 2019 00:13

Thesis Files

PDF - Final Version
See Usage Policy.


Repository Staff Only: item control page