Project: CAREER: Cryptic sulfur cycling and organic matter preservation in marine oxygen deficient zones

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. This course aims to make undergraduate research opportunities in the Earth Science Department more inclusive and accessible to minoritized students. 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 from diverse backgrounds in research.