Table of Contents

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

This dataset represents water column Thorium-234 data from the SalpPOOP, Tangaroa Cruise 1810 (aka SalpPOOP cruise). Salinity and density were measured using a CTD.  4-liter (L) samples for total water-column 234Th activity were collected using CTD bottles at approximately 12 depths from the surface to approximately 300 meters.  Samples were acidified with nitric acid to a pH < 2, and a Th-230 tracer spike was added.  Samples were shaken and allowed to equilibrate for 4 to 9 hours.  Samples were then re-basified with ammonium hydroxide to a pH of 8-9, shaken, and allowed to equilibrate for more than 8 hours.  Samples were then vacuum filtered at high vacuum pressure through a quartz (QMA) filter.  Filters were mounted in RISO planchets and counted on a RISO low-level beta multi-counter at Palmer Station, Antarctica.  Following a background count > 6 months later, samples were dissolved in 8M nitric acid / 10% hydrogen peroxide solution and a Th-229 tracer spike was added.  Samples were then analyzed on an ICP-MS to quantify the Th-229:Th-230 ratio, which was used to calculate the initial precipitation and filtration yield of Th-234.  Protocols from Pike et al. (2005) were followed. 

For additional sampling details see Decima et al. (in review, Nat. Comm.).

BCO-DMO Processing description:
- Converted collection date column and added column for ISO date format (YYYY-MM-DDThh:mmZ)
- Adjusted field/parameter names to comply with BCO-DMO naming conventions
- Added a conventional header with dataset name, PI names, version date
- Added a column for Cruise ID
- Added columns for “Latitude” and “Longitude”
- Rounded columns: “Latitude”, “Longitude”, “Depth”, “U238_activitiy”, “Th234_activity”, and “Th234_measurement_uncertainty” to 3 decimal places (or to the thousandth place)
 

NSF Award Abstract:
Salps are unique open-ocean animals that range in size from a few millimeters to greater than twenty centimeters, have a gelatinous (jelly-like) body, and can form long chains of many connected individuals. These oceanic organisms act as oceanic vacuum cleaners, having incredibly high feeding rates on phytoplankton and, unusual for consumers of their size, smaller bacteria-sized prey. This rapid feeding and the salps' tendency to form dense blooms, allows them move substantial amounts of prey carbon from the surface into the deep ocean, leading to carbon dioxide removal from the atmosphere. However, salps are often considered a trophic dead-end, rather than a link, in the food web due to the assumption that they themselves are not consumed, since their gelatinous bodies are less nutritious than co-occurring crustacean prey. Along with this, salp populations are hypothesized to be increasing due to climate change. This proposal addresses these questions: 1) Do salps compete primarily with crustaceans (as in the prevailing paradigm) or are they competitors of single-celled protists, which are the dominant grazers of small phytoplankton? 2) Do salp blooms increase the efficiency of food-web pathways from tiny phytoplankton to fisheries production in nutrient-poor ocean regions?

This project will support the interdisciplinary education of a graduate student who will learn modeling and laboratory techniques in the fields of biological and chemical oceanography and stimulate international collaborations between scientists in the United States and New Zealand. Additionally, several Education and Outreach initiatives are planned, including development of a week-long immersive high school class in biological oceanography, and education modules that will serve the "scientists-in-the schools" program in Tallahassee, FL.

It is commonly assumed that salps are a trophic sink. However, this idea was developed before the discovery that protists (rather than crustaceans) are the dominant grazers in the open ocean and was biased by the difficulty of recognizing gelatinous salps in fish guts. More recent studies show that salps are found in guts of a diverse group of fish and seabirds and are a readily available prey source when crustacean abundance is low. This proposal seeks to quantify food web flows through contrasting salp-dominated and salp-absent water parcels near the Chatham Rise off western New Zealand where salp blooms are a predictable phenomenon. The proposal will leverage previously obtained data on salp abundance, bulk grazing impact, and biogeochemical significance during Lagrangian experiments conducted by New Zealand-based collaborators. The proposal will determine 1) taxon- and size-specific phytoplankton growth rate measurements, 2) taxon- and size-specific protozoan and salp grazing rate measurements, 3) compound specific isotopic analysis of the amino acids of mesozooplankton to quantify the trophic position of salps, hyperiid amphipods, and other crustaceans, 4) sediment traps to quantify zooplankton carcass sinking rates, and 5) linear inverse ecosystem modeling syntheses. Secondary production and trophic flows from this well-constrained ecosystem model will be compared to crustacean-dominated and microbial loop-dominated ecosystems in similarly characterized regions (California Current, Costa Rica Dome, and Gulf of Mexico).

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.