Table of Contents

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

Seawater properties and biogeochemical parameters of bottom boundary layer samples from Oregon shelf and slope collected during ten cruises over three years. Most samples are from two repeat stations at ~30 m and 80 m water depth. This project is affiliated with the Coastal Endurance Array of the Ocean Observatories Initiative (OOI). https://www.bco-dmo.org/program/661079

These data come from in situ sensor measurements or analyses of water samples collected during a series of cruises on the R/V Oceanus. The ship’s SeaBird CTD system with a rosette of 12 10-L Niskin bottles was deployed for each reported event. Typically water samples were collected in the benthic boundary layer by tripping several Niskins within 4 m of the bottom. Compiled data include the water temperature, salinity and dissolved oxygen (SBE-43 sensor) recorded at the time a bottle was closed. The Niskins were sampled back onboard for Winkler determinations of dissolved oxygen, TCO2/pCO2 samples poisoned, capped and stored in brown glass bottles, nutrient samples (stored frozen until analyses), and water that was filtered onboard onto pre-combusted GF/F filters for determinations of total suspended solids and the organic C and total N content of those solids. Methods details are oxygen concentrations were measured by whole bottle Winkler titration of 125 ml samples using an amperometric method for detecting the triiodide ion reaction endpoints. TCO2 and pCO2 are determined on the same sample by methods described in Hales et al. (2017) [Estuaries and Coasts, vol 40:173-186]. Nutrient samples were stored frozen in acid-washed Nalgene™ 60 ml HDPE bottles until thawed and analyzed using standard colorimetric methods as adapted for autoanalyzers. The POC/PN water samples were immediately filtered through precombusted (at 400°C for 4 h) 25 mm Whatman™ GF/F filters. These filters were frozen at sea then later exposed to acid fumes in the laboratory for 24 h to remove inorganic carbon. Dried filters were analyzed using an elemental analyzer.

BCO-DMO Data Manager Processing Notes: * added a conventional header with dataset name, PI name, version date * modified parameter names to conform with BCO-DMO naming conventions * blank values in this dataset are displayed as "nd" for "no data." nd is the default missing data identifier in the BCO-DMO system. * removed all spaces in headers and replaced with underscores * removed all units from headers * restructured excel sheet to eliminate merged cells for pipeline intake * removed a comment in row 80 for all nutrient samples that read "Nutrient bottle #1 spilled during analysis: lost" * created an ISO_DateTime_UTC column from the Date_UTC column * put the Date_PST column in ISO format * set Types for each data column * changed cruise ID OC1807B to OC1807A * rounded TSS and CTD_DO_2 to 2 digits

NSF Award Abstract:
The longstanding theory regarding the formation of low oxygen zones in coastal shelf regions at the eastern boundaries of the oceans has pointed to the upwelling of oxygen-depleted waters from off of the shelf. In other words, dense water from beyond the shelf break that is depleted in dissolved oxygen is drawn along the seafloor upwards onto the shelf, mixing with the oxygenated water there, and creating low oxygen (hypoxic) zones. This is a paradigm that the researcher in this project seeks to shift by analyzing the added effects of respiration in shelf sediments. The investigator hypothesizes that changes in the biological activity of sediments due to seasonal changes in organic matter input from overlying waters are a major factor in the changes in dissolved oxygen content of deep shelf water, perhaps being the leading variable in the creation of hypoxic zones. Though the field analysis will be confined to the Oregon margin, there is a great deal of applicability for this research in other coastal regions where hypoxic zones form. In addition to the potential for unraveling complex local feedbacks between physical and biogeochemical processes, the researcher plans to work with a small business called Analytical Instrument Systems to build a new oxygen sensor, called a rotating disc microelectrode (RDME), that does not intrude on the environment it is testing and that can be deployed for much longer periods of time than currently popular sensors, micro-optodes. Her RDME will be deployed with micro-optodes for comparison and to validate the necessity for the RDME in the study of coastal ecosystems. This project will provide a unique experience for a postdoctoral researcher as well as a graduate and three undergraduate students. A public database will be created which will greatly help with accessibility and archiving of data for anyone who is interested in similar research. The database will be connected with a variety of other ocean observing data products, which will allow the research community and the public to make connections outside of this particular field of study. This investigator has a strong track record of including Research Experiences for Undergraduates (REU) students in her research, and she will continue to do so in this project.

The researcher aims to challenge the paradigm that hypoxic zones on the Oregon shelf are created by upwelling of offshelf oxygen-depleted water and that most of the local primary productivity is exported off the shelf during downwelling periods. Preliminary data suggests the possibility that seasonal benthic respiration may be a major factor in hypoxic water formation on the shelf. With the use of eddy covariance measurements, sediment core incubations, and near seabed particulate organic matter (POM) collections, the biogeochemical fluxes of the Oregon margin will be characterized for every season. This work is ambitious on its own, but the investigator also plans to incorporate the development of a new oxygen sensor called a rotating disc microelectrode (RDME) that will be compared to currently popular micro-optodes when making eddy covariance measurements. The RDME will be small enough as not to interfere with the physical properties being measured in situ; it will be insensitive to flow and deployable for longer periods of time. Not only does this project contain the possibility of completely overturning the current best theory of hypoxic zone formation on shelf margins, but the use of eddy covariance is new to the study of dynamic coastal ecosystems and will yield great insights into the biogeochemical processes of shelf benthos.

This project is affiliated with the Coastal Endurance Array of the Ocean Observatories Initiative (OOI): https://www.bco-dmo.org/program/661079