Table of Contents

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

This dataset presents sedimentary radium isotope activities around Guaymas Basin.

Samples for this dataset were collected as push cores using the HOV Alvin submersible. Analytical methods for measuring particulate Ra-224 and Th-228 are based on methods described in Cai et al. (2012; 2014). In short, once the cores were recovered on the ship, overlying waters were siphoned off and the sediment cores were sectioned in 2 cm vertical intervals for the top 10 cm, then 4 cm intervals for the remainder of the core. A slurry was prepared by adding ~¼ of the sediment volume (or ~1/8 of the sediment volume for the 4 cm intervals) to 150 mL of Ra-free tap water. The pH of the slurry was adjusted by adding 5-10 drops of concentrated NH3-OH, after which 1 mL of 19 mM KMnO4 and 1 mL of 40 mM MnCl2 solutions were added to precipitate any dissolved radium and thorium. A portion of this slurry was vacuum-filtered onto pre-weighed 47 mm diameter GFF filters until no further drops passed through the filter. Filters were dried in a drying oven (at 60 °C) for 12 hours, then placed is a filter holder within a cartridge and counted on a Radium Delayed Coincidence Counter (Moore and Arnold, 1996). Results from this analysis represent particulate Ra-224 activities. Filters were then measured on the Radium Delayed Coincidence Counter again after 3 weeks, from which the results are representative of Th-228 activities on the sediments.

BCO-DMO Processing:
- modified parameter names (changed hyphens to underscores; replaced spaces with underscores);
- formatted date/time to ISO 8601 format;
- corrected rows with value of "2019" as the year (changed to "2016");
- saved Radium Delayed Coincidence Counter calibrations as PDF - see Supplemental Files.

NSF Award Abstract:
This project proposes to validate a new approach to measure porewater flow dynamics from deep sea sediments using a biologically conservative, naturally-occurring tracer, Radium 224, which is constantly produced by porewaters. The technique will be validated using independent measures of porewater fluxes (i.e. heat gradients and magnesium profiles) during a cruise to the Guaymas Basin in the Gulf of California that is already funded by NSF. Once validated the technique will be broadly applicable to all sedimentary environments including oceans, rivers/streams, wetlands and lakes. Understanding porewater flow dynamics is important to understanding ocean and other aquatic system chemical budgets, microbial ecology and global heat flow.

This proposal hypothesizes that the short-lived radium isotope Ra 224 may serve as an effective tracer of porewater flows in deep ocean systems, regardless of the type or composition of seepages, because its sources and sinks can be uniquely constrained. The method will be tested in the Guaymas Basin which is comprised of areas undergoing a range of seepage rates and offers porewater thermal gradients resulting from the hydrothermal system. As a result heat fluxes and gradients in magnesium and other cations affected by high-temperature water/rock interactions can be used to independently validate the porewater flows measured by Ra 224.