Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Sediments were collected with push cores (6 cm inner diameter) along three depth transects across the Santa Barbara Basin using the ROV Jason.  Porewater was separated from sediment by centrifugation (4300 x g for 20 mins) in anoxic centrifugation vials and subsampled for further analysis. 

Porewater geochemical properties were determined as listed:

• Porewater sulfate concentrations were determined by ion chromatography (Metrohm 761).
• Porewater sulfide concentrations were determined spectrophotometrically (Shimadzu UV-Spectrophotometer UV-1800) according to Cline (1969).
• Porewater ammonium, iron (II), and phosphate concentrations were determined spectrophotometrically (Shimadzu UV-Spectrophotometer UV-1800) according to Grasshoff et al. (1999).
• Porewater nitrate and nitrite concentrations were determined spectrophotometrically (Shimadzu UV-Spectrophotometer UV-1800) according to García-Robledo et al. (2014).
• Porewater Total Alkalinity was determined by titration according to Dale et al. 2015. Porewater Dissolved Inorganic Carbon was determined using a flow injection system (Hall & Aller 1992).

Note:  Negative depths refer to measurements in the sediment core supernatant water.  Supernatant water was collected with an anoxic syringe prior to core slicing. 

BCO-DMO Data Processing
- Imported data from source file "Treude_Valentine_BASIN_2019_datasets_BCO-DMO.xlsx" into the BCO-DMO processing tool
- Combined data from multiple stations into a single file
- Separated data for porewater, microbial, and sediment into individual tables
- Modified parameter (column) names to conform with BCO-DMO naming conventions
      The only allowed characters are A-Z,a-z,0-9, and underscores
       No spaces, hyphens, commas, parentheses, or Greek letters
-  Added column for Cruise
- Changed date format from m/d/yyyy to yyyy-mm-dd (ISO Date 8601 format)
- Added conventional header with dataset name, PI name, version date

NSF Award Abstract:
This study focuses on chemical processes that occur in oxygen-limited waters along the world's continental margins. These processes are influenced by the activities of microbes and control the fate of key elements that are deposited to sediments in these areas including carbon, nitrogen and sulfur. As a result, they are key to the health and function of the ocean. The intellectual merit of this research is to study the coupled chemical and microbial processes that occur in these environments by combining robotic technology with experiments that will be conducted at the ocean floor and in the shipboard laboratory. The broader impacts of this project will provide at-sea training and educational opportunities to undergraduate and graduate students and the results will be broadly distributed to stakeholders and interested parties. Results from this research promise to identify and quantify rates for key processes that couple carbon, nitrogen and sulfur in marine environments adjacent to the continents. The project addresses an important aspect of environmental change in the ocean (i.e., decreased oxygen due to warming and nutrient enrichment) and its influence on chemical and biological cycles and ocean ecosystems.

The dynamics of oxygen minimum zones along continental margins, and their potential for future expansion, are important because of their intersection with global biogeochemical cycles and because of their far-reaching impacts on ocean ecosystems. However, the impacts of transient deoxygenation on biogeochemical cycles of carbon, nitrogen and sulfur at the sea floor are not well established and are the focus of this study. This study will test the overarching hypothesis that deoxygenation triggers a positive feedback loop between bacterial mats at the sea floor that consume hydrogen sulfide, a sulfur species that can be toxic to higher organisms, and an underlying community of bacteria that produce hydrogen sulfide. By this hypothesis, the establishment of sea floor mats, which depend on inorganic nitrogen sources to run their sulfur metabolism, accelerates nitrogen cycling in the uppermost sediment horizon following deoxygenation. The accelerated nitrogen cycling allows for upward expansion of the sulfide-producing bacteria, which in-turn provide a shallow source of sulfide as substrate to further support nitrogen cycling in the sea floor mat. The results of this study will enable understanding of the relationship between oxygen dynamics in the water column and the biogeochemical processes at the sea floor that link the transformations of carbon, nitrogen and sulfur. The results of this study promise to define the environmental conditions under which the sulfur and nitrogen cycles are coupled and subject to strong positive feedbacks at the seafloor, as well as the conditions under which they are decoupled. This study provides training in research and innovative analytical and experimental techniques to four graduate students and several undergraduates. Undergraduates will be engaged in research at two institutions, one of which has recently been designated as a Hispanic serving institution. Approximately 10 undergraduate students (20 in total) will participate in each of the two proposed oceanographic expeditions, through an established course entitled: Field Studies in Marine Biogeochemistry. This course provides an opportunity for students to develop an independent research project in advance of the expedition, to participate on the expedition, and to conduct research projects while at sea.

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.