Table of Contents

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

At sea, Radium-226 samples were collected following the GEOTRACES cookbook. Samples were collected from a 30-liter (L) Niskin mounted directly above a McLane large volume in situ pump WTS-LV (>1000 meters) or on a CTD Rosette (<1000 meters). These samples (10-25 L) were gravity-filtered through 15 grams (g) of manganese oxide impregnated acrylic fiber at approximately 0.5 liters per minute (L/min). The filtrate was collected inside of a graduated rigid sided container and the volume was recorded. A mass was also obtained by using a hand-held digital balance.

The Mn fibers from the Niskin bottles were rinsed with deionized water back at Woods Hole Oceanographic Institution (WHOI), partially dried, and sealed within a fiber holder after being flushed with helium equivalent to 30 column volumes. Samples were stored for a minimum of 12 days and analyzed for 226Ra via 222Rn ingrowth using alpha scintillation counting (Key et al., 1979). Samples were counted for 1-20 hours depending on the activity on the fiber, which resulted in counting uncertainties of ~2% dependent upon 226Ra content on the fiber and sample volume.

Radium-228 was collected on manganese-coated cartridges filtered at depth using an adapted McLane in situ pump (WTS-LV). The pumps were programmed to filter 1500-2000L of seawater per deployment. The cartridges were rinsed with radium-free fresh water and excess moisture was removed using compressed air. Samples were analyzed multiple times using a delayed coincidence counter (RaDeCC) for determination of radium-228 via thorium-228 ingrowth. At selected stations, samples were ashed in a muffle furnace at 820 degrees Celsius for 24 hours and the fiber ash was transferred to polystyrene vials, sealed with epoxy (to prevent 222Rn loss), and counted on high purity, well-type germanium detectors to measure 228Ra, using the lines of 228Ac (338 keV, 911 keV, and 969 keV).

In addition to the water column samples, large volume surface samples were collected by pumping from a depth of 2 meters through a single Mn-cartridge accompanied by a 15-25-liter sample that was passed through a 15 g Mn-fiber column to retain radium-226.

Data Processing:
The data were corrected for decay from the time of sampling. Data is originally calculated in disintegrations per minute per liter (dpm/L) and is converted to milli-Becquerels per kilogram (mBq/kg) using the standard ocean rho = 1.0235 kg/L and 1 dpm = 16.667 mBq.

Quality Flags:
Data were flagged using the SeaDataNet quality flag scheme. Two additional flags, 'B' and 'C' (defined below), were 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;
A = Value phenomenon uncertain;
B = Value obtained from Radium/Barium ratio;
C = Value measured through gamma spectroscopy.

*Version 1:*
version 1 date: 2020-10-01
- renamed fields to comply with BCO-DMO naming conventions;
- added date/time columns in ISO 8601 format;
- replaced "N/A" with "nd" to indicate "no data".

*Version 2:*
version 2 date: 2021-12-15
- same as version 1, plus made the following correction to the Event_ID column: replaced event number 6647 with 6656 for samples 13251-13262. Published as version 2.

*Version 3:*
version 3 date: 2022-09-28
- imported two Excel files, "BCODMO GP15 Charette 226Radium leg1.xlsx" and "BCODMO GP15 Charette 228Radium leg1.xlsx", into the BCO-DMO system;
- joined the two files, using Event_ID and Sample_ID as they key, to create a single dataset;
- renamed the 'Flag' field for Ra228 to follow GEOTRACES naming conventions;
- renamed the Ra-228 fields using the parameter names assigned by the GEOTRACES DOoR portal;
- saved the final file as "825891_v3_gp15_ra226_ra228_leg1.csv"
- note that in the final csv file, missing data are blank/empty.

A 60-day research cruise took place in 2018 along a transect form Alaska to Tahiti at 152° W. A description of the project titled "Collaborative Research: Management and implementation of the US GEOTRACES Pacific Meridional Transect", funded by NSF, is below. Further project information is available on the US GEOTRACES website and on the cruise blog. A detailed cruise report is also available as a PDF.

Description from NSF award abstract:
GEOTRACES is a global effort in the field of Chemical Oceanography in which the United States plays a major role. The goal of the GEOTRACES program is to understand the distributions of many elements and their isotopes in the ocean. Until quite recently, these elements could not be measured at a global scale. Understanding the distributions of these elements and isotopes will increase the understanding of processes that shape their distributions and also the processes that depend on these elements. For example, many "trace elements" (elements that are present in very low amounts) are also important for life, and their presence or absence can play a vital role in the population of marine ecosystems. This project will launch the next major U.S. GEOTRACES expedition in the Pacific Ocean between Alaska and Tahiti. The award made here would support all of the major infrastructure for this expedition, including the research vessel, the sampling equipment, and some of the core oceanographic measurements. This project will also support the personnel needed to lead the expedition and collect the samples.

This project would support the essential sampling operations and infrastructure for the U.S. GEOTRACES Pacific Meridional Transect along 152° W to support a large variety of individual science projects on trace element and isotope (TEI) biogeochemistry that will follow. Thus, the major objectives of this management proposal are: (1) plan and coordinate a 60 day research cruise in 2018; (2) obtain representative samples for a wide variety of TEIs using a conventional CTD/rosette, GEOTRACES Trace Element Sampling Systems, and in situ pumps; (3) acquire conventional CTD hydrographic data along with discrete samples for salinity, dissolved oxygen, algal pigments, and dissolved nutrients at micro- and nanomolar levels; (4) ensure that proper QA/QC protocols are followed and reported, as well as fulfilling all GEOTRACES intercalibration protocols; (5) prepare and deliver all hydrographic data to the GEOTRACES Data Assembly Centre (via the US BCO-DMO data center); and (6) coordinate all cruise communications between investigators, including preparation of a hydrographic report/publication. This project would also provide baseline measurements of TEIs in the Clarion-Clipperton fracture zone (~7.5°N-17°N, ~155°W-115°W) where large-scale deep sea mining is planned. Environmental impact assessments are underway in partnership with the mining industry, but the effect of mining activities on TEIs in the water column is one that could be uniquely assessed by the GEOTRACES community. In support of efforts to communicate the science to a wide audience the investigators will recruit an early career freelance science journalist with interests in marine science and oceanography to participate on the cruise and do public outreach, photography and/or videography, and social media from the ship, as well as to submit articles about the research to national media. The project would also support several graduate students.

NSF Award Abstract:
The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Naturally occurring radioactive isotopes of the element radium can be used to measure the rates of important processes in the ocean. In turn, making these rate measurements at the same time as other trace element and isotope data are collected enables a more complete interpretation of these data. The investigators propose to measure the four isotopes of radium -- Ra-223, Ra-224, Ra-226, and Ra-228 -- on a U.S. GEOTRACES expedition from Alaska to Tahiti in 2018. The radium isotope data will be particularly useful in investigating trace element input and removal processes associated with ocean boundaries (rivers, continental shelves, and the ocean bottom) and with mid-ocean ridge hydrothermal vents and the long-range dispersal of their neutrally buoyant plumes. The investigators will also investigate the processes controlling the internal cycling of the longest-lived isotope, Ra-226, compared to the element barium, which has a very similar chemistry to radium.
 
The proposed work would address a number of key questions regarding trace element inputs from ocean boundaries and their potential impact on ocean productivity and biogeochemistry. As iron is an important nutrient for marine phytoplankton, the investigators will quantify the rates of lateral trace element transport from the Gulf of Alaska margin out to and including the offshore High Nutrient Low Chlorophyll region of the subarctic Northeast Pacific Ocean. In the ocean subsurface, they will seek to understand the trace element fluxes associated with high temperature hydrothermal venting, and the rate at which trace elements and isotopes are removed via scavenging along the hydrothermal plume. Lastly, the work will lead to an improved understanding of a marine carbonate sediment dating technique via an investigation of Ra-226 and barium fractionation processes in the upper ocean. The project will involve collaboration between two U.S. institutions and a partner in France who will analyze some of the samples. Two graduate students will participate in the project. Moore will supervise an undergraduate student through the South Carolina Alliance for Minority Participation, and will encourage this student to develop a senior thesis based on their participation in this project.

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.