Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Curation Notes
  • Problem Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Because of their short half-life, Radium-223 and Radium-224 were measured onboard from large-volume samples via delayed coincidence counting (RaDeCC, Moore & Arnold, 1996), immediately after collection from the Mn-coated cartridges, and after rinsing with Ra-free water and drying to dampness. Radium-223, Radium-224, and Radium-228 were collected on manganese-coated cartridges filtered at depth using an adapted McLane in situ pump (WTS-LV). The pumps were programmed to filter 1500-2000 liters (L) of seawater per deployment. The cartridges were rinsed with radium-free fresh water, and excess moisture was removed using compressed air. In addition to the water column samples, large-volume surface samples were collected by pumping from a depth of 2 meters through via a hand-deployable pump through 2 pre-filters, a single Mn-cartridge accompanied by a 15-25 liter sample that was passed through a 20 gram (g) Mn-fiber column to retain radium.

Radium-228 was measured via RaDeCC through Th-228 ingrowth. Cartridge efficiency was individually corrected from comparaison between Ra-226 on cartridge and fiber samples. For select samples (DQ flag = C), Ra-228 was counted from the large volume samples via gamma spectroscopy for Ra-226, Ra-228, and Th-228 following the methods from Moore et al. (2024). The Mn cartridges were ashed in a muffle furnace at 820 degrees Ceslius (˚C) for 48 hours, transferred to 15 or 25 millimeter (mm) diameter polystyrene vials and sealed with epoxy to prevent Rn-222 loss. After waiting at least three weeks for daughter isotopes to reach equilibrium, the samples were counted from 3-6 days in high purity, well-type germanium detectors at WHOI laboratories. Ra-226 activities were quantified via the Pb-214 photopeak at 352 keV and Ra-228 was quantified via the Ac-228 photopeaks at 338 and 911 keV.

The data were corrected for decay from the time of sampling. 223Raxs was corrected for 227Ac, 224Raxs was corrected for 228Th. The radium activity of the water samples (cartridges) were corrected from the measured radium and actinium on acrylic fiber (<1L/minute) using the emanation technique. Data are originally calculated in disintegrations per minute per liter (dpm/L) and are converted to milli-Becquerels per kilogram (mBq/kg) using the in situ density (rho) from the deployment at time of sampling (ODF) or the nearest available depth for the station (surface and McLane pumps).

Quality Flags:
Data were flagged using the SeaDataNet quality flag scheme. One additional flag, 'C' (defined below), was also assigned to this dataset. For more information on SeaDataNet flags, see: https://www.geotraces.org/geotraces-quality-flag-policy/ and https://www.seadatanet.org/Standards/Data-Quality-Control.

Quality flag definitions:
0 = No quality control;
1 = Good value;
2 = Probably good value;
3 = Probably bad value;
4 = Bad value;
5 = Changed value;
6 = Value below detection;
7 = Value in excess;
8 = Interpolated value;
9 = Missing value;

C = Ra data from Gamma Spectroscopy

- Imported original file "mbq_Kg_223_224_228_Radium.csv" into the BCO-DMO data processing system.
- Set "BDL" as a missing data value (note that missing data are empty/blank in the final CSV blank, and BDL is indicated by the 'Flag' columns).
- Renamed columns to comply with BCO-DMO naming conventions.
- Removed values of "0" (no data) in Start_ISO_DateTime_UTC column.
- Saved the final file as "11007766_v1_gp17oce_ra23_224_228.csv".

- Imported original, supplemental file "DPM_223_224_228_Radium.csv" into the BCO-DMO data processing system.
- Set "BDL" as a missing data value (note that missing data are empty/blank in the final CSV blank, and BDL is indicated by the 'Flag' columns).
- Removed values of "0" (no data) in Start_ISO_DateTime_UTC column.
- Saved the final file as "dpm_223_224_228_radium.csv".

NSF Award Abstract:
The GEOTRACES program aims to understand the distribution of trace elements and their isotopes in the oceans. Trace elements, by their very nature, are scarce. Despite their scarcity, trace elements are valuable tools for studying marine processes, such as: tracking chemical inputs to the ocean from the land or seafloor, identifying patterns of ocean mixing, and tracing ocean biology. This project will study these processes by measuring and modeling the distributions of two chemically similar elements — radium and barium. These measurements will be made on samples collected as part of the U.S. GEOTRACES GP17-OCE expedition. This expedition will collect samples from the Southern Ocean in late 2022. The Southern Ocean experiences deep mixing, which is important for bringing nutrients to the sea surface. Measuring radium and barium isotopes in these samples will help study the sources, cycling, and sinks of nutrients that support marine biology in the Southern Ocean and beyond. The findings will be shared with regional science teachers and students through a collaboration with the local Sea Grant Program, and the data will support the research of other scientists involved in GEOTRACES.

The last 25 years have seen a paradigm shift in our understanding of the controls on marine nutrient cycles. Rather than arising from local vertical processes, the large-scale distributions of many elements are now thought to arise from processes occurring in the Southern Ocean, which are then communicated to lower latitudes through lateral circulation. A circulation-driven mechanism is also hypothesized to contribute to the global distributions of radium and barium isotopes, but this remains to be tested. In this project, researchers from the Woods Hole Oceanographic Institution will test this hypothesis by analyzing radium and barium isotopes in dissolved and particulate samples collected from the Pacific Sector of the Southern Ocean. These measurements will establish compositions for the southern-sourced mode/intermediate and bottom waters that are important end-members in the global overturning circulation. The team will also study the processes that control the composition of the end-members — particle formation and dissolution, interactions with sediments, hydrothermalism — and assess their significance using statistical and mechanistic modeling. The results will reveal the role of the Southern Ocean in controlling the global distributions of radium and barium isotopes, which will help refine the application of these tracers as tools for studying biogeochemical processes in the present and past oceans.

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.

NSF Award Abstract:
The goal of the GEOTRACES program is to “identify processes and quantify fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean and to establish the sensitivity of these distributions to changing environmental conditions”. This ambitious objective requires coordinated seagoing field work for collection of samples to measure many elements simultaneously across the earth’s major ocean basins. However, these comprehensive global concentration maps for trace elements cannot be properly interpreted without concurrent measurement of radioactive tracers like radium isotopes that can provide time scales of their ocean input. In this project, the investigators will measure the abundance and distribution of radium isotopes in the Southern Ocean between the southern tip of South America and Antarctica, including a detailed characterization of the Antarctic coastal marine environment. The project will support a postdoctoral research associate and involve two undergraduate student researchers in post-cruise analyses.

The main motivation of the proposed research is to utilize the quartet of radium (Ra) isotopes (224Ra, 223Ra, 228Ra, 226Ra) to enable source identification and flux quantification of TEIs during the forthcoming US GEOTRACES GP17-OCE and GP17-ANT expeditions. Measurement of Ra isotopes will allow the team to address several key questions related to ocean margin and benthic boundary processes and their role in supplying and transporting TEIs to marine ecosystems including: (1) What are the rates of lateral transport of TEIs from the Antarctic and Patagonian continental margins out to and including the high nutrient low chlorophyll (HNLC) Southern Ocean? (2) What are the TEI fluxes associated with Antarctic glacial meltwater? and (3) What are the time scales of TEI transport associated with Pacific-Antarctic Ridge neutrally buoyant hydrothermal plumes? Boundary inputs are considered to be the dominant source of many key TEIs to the ocean including iron, however, TEI concentrations must be coupled with input and transport rates to determine their effect on marine biogeochemical cycles. The wide range of Ra isotope half-lives (3.66 days to 1600 years) allow for the quantification of TEI transport processes on time scales relevant to ocean mixing processes. The proposed coupled Ra-TEI measurements will allow the full value of the distribution of numerous TEIs as measured by GEOTRACES PIs to be realized.

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.

The U.S. GEOTRACES GP17-OCE expedition departed Papeete, Tahiti (French Polynesia) on December 1st, 2022 and arrived in Punta Arenas, Chile on January 25th, 2023. The cruise took place in the South Pacific and Southern Oceans aboard the R/V Roger Revelle (cruise ID RR2214) with a team of 34 scientists lead by Ben Twining (Chief Scientist), Jessica Fitzsimmons and Greg Cutter (Co-Chief Scientists). GP17 was planned as a two-leg expedition, with its first leg (GP17-OCE) as a southward extension of the 2018 GP15 Alaska-Tahiti expedition and a second leg (GP17-ANT; December 2023-January 2024) into coastal and shelf waters of Antarctica's Amundsen Sea.

The South Pacific and Southern Oceans sampled by GP17-OCE play critical roles in global water mass circulation and associated global transfer of heat, carbon, and nutrients. Specific oceanographic regions of interest for GP17-OCE included: the most oligotrophic gyre in the global ocean, the Antarctic Circumpolar Current (ACC) frontal region, the previously unexplored Pacific- Antarctic Ridge, the Pacific Deep Water (PDW) flow along the continental slope of South America, and the continental margin inputs potentially emanating from South America.

Further information is available on the US GEOTRACES website and in the cruise report (PDF).

NSF Project Title: Collaborative Research: Management and Implementation of US GEOTRACES GP17 Section: South Pacific and Southern Ocean (GP17-OCE)

NSF Award Abstract:
This award will support the management and implementation of a research expedition from Tahiti to Chile that will enable sampling for a broad suite of trace elements and isotopes (TEI) across oceanographic regions of importance to global nutrient and carbon cycling as part of the U.S. GEOTRACES program. GEOTRACES is a global effort in the field of Chemical Oceanography, the goal of which is to understand the distributions of trace elements and their isotopes in the ocean. Determining the distributions of these elements and isotopes will increase understanding of processes that shape their distributions, such as ocean currents and material fluxes, and also the processes that depend on these elements, such as the growth of phytoplankton and the support of ocean ecosystems. The proposed cruise will cross the South Pacific Gyre, the Antarctic Circumpolar Current, iron-limited Antarctic waters, and the Chilean margin. In combination with a proposed companion GEOTRACES expedition on a research icebreaker (GP17-ANT) that will be joined by two overlapping stations, the team of investigators will create an ocean section from the ocean's most nutrient-poor waters to its highly-productive Antarctic polar region - a region that plays an outsized role in modulating the global carbon cycle. The expedition will support and provide management infrastructure for additional participating science projects focused on measuring specific external fluxes and internal cycling of TEIs along this section.

The South Pacific Gyre and Pacific sector of the Southern Ocean play critical roles in global water mass circulation and associated global transfer of heat, carbon, and nutrients, but they are chronically understudied for TEIs due to their remote locale. These are regions of strong, dynamic fronts where sub-surface water masses upwell and subduct, and biological and chemical processes in these zones determine nutrient stoichiometries and tracer concentrations in waters exported to lower latitudes. The Pacific sector represents an end member of extremely low external TEI surface fluxes and thus an important region to constrain inputs from the rapidly-changing Antarctic continent. Compared to other ocean basins, TEI cycling in these regions is thought to be dominated by internal cycling processes such as biological uptake, regeneration, and scavenging, and these are poorly represented in global ocean models. The cruise will enable funded investigators to address research questions such as: 1) what are relative rates of external TEI fluxes to this region, including dust, sediment, hydrothermal, and cryospheric fluxes? 2) What are the (micro) nutrient regimes that support productivity, and what impacts do biomass accumulation, export, and regeneration have on TEI cycling and stoichiometries of exported material? 3) What are TEI and nutrient stoichiometries of subducting water masses, and how do scavenging and regeneration impact these during transport northward? This management project has several objectives: 1) plan and coordinate a 55-day research cruise in 2021-2022; 2) use both conventional and trace-metal 'clean' sampling systems to obtain TEI samples, as well as facilitate sampling for atmospheric aerosols and large volume particles and radionuclides; 3) acquire hydrographic data and samples for salinity, dissolved oxygen, algal pigments, and macro-nutrients; and deliver these data to relevant repositories; 4) ensure that proper QA/QC protocols, as well as GEOTRACES intercalibration protocols, are followed and reported; 5) prepare the final cruise report to be posted with data; 6) coordinate between all funded cruise investigators, as well as with leaders of proposed GP17-ANT cruise; and 7) conduct broader impact efforts that will engage the public in oceanographic research using immersive technology. The motivations for and at-sea challenges of this work will be communicated to the general public through creation of immersive 360/Virtual Reality experiences, via a collaboration with the Texas A&M University Visualization LIVE Lab. Through Virtual Reality, users will experience firsthand what life and TEI data collection at sea entail. Virtual reality/digital games and 360° experiences will be distributed through GEOTRACES outreach websites, through PI engagement with local schools, libraries, STEM summer camps, and adult service organizations, and through a collaboration with the National Academy of Sciences.

GEOTRACES is a SCOR sponsored program; and funding for program infrastructure development is provided by the U.S. National Science Foundation.

GEOTRACES gained momentum following a special symposium, S02: Biogeochemical cycling of trace elements and isotopes in the ocean and applications to constrain contemporary marine processes (GEOSECS II), at a 2003 Goldschmidt meeting convened in Japan. The GEOSECS II acronym referred to the Geochemical Ocean Section Studies To determine full water column distributions of selected trace elements and isotopes, including their concentration, chemical speciation, and physical form, along a sufficient number of sections in each ocean basin to establish the principal relationships between these distributions and with more traditional hydrographic parameters;

* To evaluate the sources, sinks, and internal cycling of these species and thereby characterize more completely the physical, chemical and biological processes regulating their distributions, and the sensitivity of these processes to global change; and

* To understand the processes that control the concentrations of geochemical species used for proxies of the past environment, both in the water column and in the substrates that reflect the water column.

GEOTRACES will be global in scope, consisting of ocean sections complemented by regional process studies. Sections and process studies will combine fieldwork, laboratory experiments and modelling. Beyond realizing the scientific objectives identified above, a natural outcome of this work will be to build a community of marine scientists who understand the processes regulating trace element cycles sufficiently well to exploit this knowledge reliably in future interdisciplinary studies.

Expand "Projects" below for information about and data resulting from individual US GEOTRACES research projects.