Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • BCO-DMO Processing Description
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Total 234Th was measured using standard small volume techniques (Benitez-Nelson et al., 2001; Pike et al., 2005). 4-liter (L) samples for total 234Th were sampled using a CTD Niskin rosette (typically from eight depths spanning the epipelagic). Samples were acidified to a pH of <2 with HNO3. A tracer addition of 230Th was added and samples were mixed vigorously. Samples were allowed to equilibrate for 4-9 hours and then adjusted to a pH of 8-9 with NH4OH. KMnO4 and MnCl2 were added and samples were mixed and allowed to sit for ~12 hours as Th co-precipitated with manganese oxide. Samples were then vacuum-filtered at high pressure onto QMA filters, dried, and mounted in RISO sample holders.

Samples were beta counted on a RISO low-level background beta counter at Palmer Station and re-counted >6 half-lives later. Samples for water-column 234Th were then dissolved in HNO3/H2O2 solution and 229Th tracer was added. Samples were evaporated and reconstituted in dilute nitric acid / hydrofluoric acid. They were then analyzed by inductively-coupled plasma mass spectrometry at the Woods Hole Oceanographic Institution Analytical Lab to determine the ratio of 229:230Th to determine the initial yield of the 234Th filtration. 238U activity (for estimating 238U-234Th deficiency) was estimated from a linear relationship with salinity (Owens et al., 2011).

- Imported original file "Th Logs - ForBCODMO - 2024-07-03.xlsx" into the BCO-DMO system.
- Renamed fields to comply with BCO-DMO naming conventions.
- Converted the local date-time column to ISO 8160 format.
- Added a date-time column in UTC.
- Saved the final file as "945225_v1_th-234_wap.csv"

NSF Award Abstract:
Algae in the surface ocean convert carbon dioxide into organic carbon through photosynthesis. The biological carbon pump transports this organic carbon from the atmosphere to the deep ocean where it can be stored for tens to hundreds of years. Annually, the amount transported is similar to that humans are currently emitting by burning fossil fuels. However, at present we cannot predict how this important process will change with a warming ocean. These investigators plan to develop a 15+ year time-series of vertical carbon transfer for the Western Antarctic Peninsula; a highly productive Antarctic ecosystem. This region is also rapid transition to warmer temperatures leading to reduced sea ice coverage. This work will help researchers better understand how the carbon cycle in the Western Antarctic Peninsula will respond to climate change. The researchers will develop the first large-scale time-series of carbon flux anywhere in the ocean. This research will also support the education and training of a graduate student and support the integration of concepts in Antarctic research into two undergraduate courses designed for non-science majors and advanced earth science students. The researchers will also develop educational modules for introducing elementary and middle-school age students to important concepts such as gross and net primary productivity, feedbacks in the marine and atmospheric systems, and the differences between correlation and causation. Results from this proposal will also be incorporated into a children’s book, “Plankton do the Strangest Things”, that is targeted at 5-7 year olds and is designed to introduce them to the incredible diversity and fascinating adaptations of microscopic marine organisms.

This research seeks to leverage 6 years (2015-2020) of 234Th samples collected on Palmer LTER program, 5 years of prior measurements (2009-2010, 2012-2014), and upcoming cruises (2021-2023) to develop a time-series of summertime particle flux in the WAP that stretches for 15 years. The 238U-234Th disequilibrium approach utilizes changes in the activity of the particle-active radio-isotope 234Th relative to its parent nuclide 238U to quantify the flux of sinking carbon out of the surface ocean (over a time-scale of ~one month). This proposal will fund 234Th analyses from nine years’ worth of cruises (2015-2023) and extensive analyses designed to investigate the processes driving inter-annual variability in the BCP. These include: 1) physical modeling to quantify the importance of advection and diffusion in the 234Th budget, 2) time-series analyses of particle flux, and 3) statistical modeling of the relationships between particle flux and multiple presumed drivers (biological, chemical, physical, and climate indices) measured by collaborators in the Palmer LTER program. This multi-faceted approach is critical for linking the measurements to models and for predicting responses to climate change. It will also test the hypothesis that export flux is decreasing in the northern WAP, increasing in the southern WAP, and increasing when integrated over the entire region as a result of earlier sea ice retreat and a larger ice-free zone. The project will also investigate relationships between carbon export and multiple potentially controlling factors including: primary productivity, algal biomass and taxonomic composition, biological oxygen saturation, zooplankton biomass and taxonomic composition, bacterial production, temperature, wintertime sea ice extent, date of sea ice retreat, and climate modes.

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.