Table of Contents

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

Samples were collected first from the non-trace metal rosette. A sampling tube was connected to the Niskin petcock. The petcock was opened followed by opening the Niskin air vent. The sampling tube was held upright so that when water flow started all bubbles were pushed out. The tube was then immersed to the bottom of a 300 milliliter (ml) BOD bottle that was placed inside a 1-liter (L) overflow container. Water was allowed to flow until it started running out of the overflow container, the tube was removed from the 300 ml BOD bottle while water was still flowing, the Niskin bottle petcock was closed, then the stopper was placed into the BOD bottle while it was still immersed in the water in the overflow bottle. The BOD bottle was inspected for the presence of bubbles. If there were bubbles, the procedure was repeated.

The UM (University of Miami) tracer lab uses a custom-built purge and trap capillary column gas chromatography method with electron capture detection to measure all compounds in a single run. The gas chromatograph was an SRI 8610. This system has been used successfully on many CLIVAR, GO-SHIP, and GEOTRACES cruises with an older Shimadzu gas chromatograph. Right before this cruise, the custom-built system was modernized with a new gas chromatograph and new instrument control and data acquisition software. N₂O peaks in the chromatogram can interfere with SF₆ peaks and by adding a 6-meter length of a mole sieve 5a capillary column to the end of the 60m Gas Pro main column, the elution of N₂O was delayed so that it is after the elution of the other four compounds. However, the attempt to quantitate the N₂O peak was not successful. This system can measure all compounds in gas standards, air, and water.

Blanks are determined by running a water method without loading a water sample into the sampling loop. The blank peak areas are subtracted from unknown samples peak areas before concentrations are calculated. One or two blanks are run for each station analyzed. Blank values are typically very consistent and very small compared to unknown peak sizes.

One duplicate water sample is collected during each station sampled. Precision is 2% or better for each parameter measured.

Standards are in the gas phase, which is a tank of compressed nitrogen containing all compounds. Standards used on this cruise were prepared at PMEL (Pacific Marine and Environmental Laboratory) and calibrated against the SIO (Scripps Institute of Oceanography) absolute calibration scale. All US-based tracer laboratories use these standards for calibration. One standard is used, and different amounts of that standard are analyzed, using a combination of five different gas sample loops to generate a calibration curve covering the range of unknows analyzed. Typical curves consist of 20 to 30 data points so that the non-liner response of the Electron Capture detector can be determined well. Calibration curves are generated at the beginning of the cruise. The detector response changes that may occur with time are monitored by analyzing a single volume of the standard, two or three times during the analysis of each station. Any drift in response is used to correct the final concentration determination.

Additional calibration curves will be generated at the end of the cruise and during the cruise if instrument conditions change.

Another check on the accuracy of the analytical technique is to measure the concentration of all the compounds in air during the cruise. The air concentration is known, and air measurements should be close to the known values. Air samples are analyzed as time permits, but at least several times during each cruise.

Surface water concentrations should be close to equilibrium with the air concentration at the time of the cruise. These values are typically within 5% of the temperature- and salinity-dependent saturation values.

Quality Flags:
Quality flags were applied following the GEOTRACES policy (https://www.geotraces.org/geotraces-quality-flag-policy/), which recommends the SeaDataNet Scheme:
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; (see attached Supplemental File for detection limits for Be-7 samples)
7 = value in excess;
8 = interpolated value;
9 = missing value;
A = value phenomenon uncertain.

- Imported original file "RR2214 GP-17 DOoR data table 2.xlsx" into the BCO-DMO system.
- Flagged "-999" as a missing data value (missing data are empty/blank in the final CSV file).
- Renamed fields to comply with BCO-DMO naming conventions.
- Removed the following empty columns: Gear_ID, End_Date_UTC, End_Time_UTC, End_Latitude, End_Longitude.
- Created date-time field in ISO 8601 format.
- Imported the PI-modified file with updated quality flags.
- Saved the final file as "959378_v1_gp17-oce_cfcs_sf6.csv".

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.

NSF Award Abstract:
The goal of the international GEOTRACES program is to understand the distributions in the ocean of trace chemical elements and their isotopes (TEIs), which are different forms of the same element. Many of the TEIs are essential for phytoplankton growth (e.g., iron) and are micronutrients. Yet, other TEIs are pollutants (e.g., lead). The U.S. GEOTRACES GP17-OCE expedition will occur in the South Pacific and Pacific sector of the Southern Ocean. Essential to understanding how TEIs change, e.g., scavenging and regeneration, and for estimating rates of biochemical processes is to identify water masses that are newly ventilated with atmospheric gases. These are waters that have been in contact with the atmosphere in the past few decades. The main objective of this project will be to measure the concentration of three man-made tracers of ocean ventilation that can be used to determine how long since a water mass was at the ocean surface in contact with the atmosphere. The tracers are particularly useful for following water masses along pathways as they age and estimating rates of effective spreading and dilution. An analogy would be adding a colored dye in the surface ocean, with a bit more dye added each year, and then measuring the concentration of this dye as surface water moves into the interior ocean. The three tracers that will be measured are Chlorofluorocarbon-11 (CFC-11), Chlorofluorocarbon-12 (CFC-12) and Sulfur Hexafluoride (SF6). The trace gas concentrations, ventilation ages, and rate data will all be made available to other investigators within six months of collection, forming an important foundation for the broader GEOTRACES program.

The project team will measure CFC-11, CFC-12, and SF6 concentrations at sea aboard the GP17-OCE expedition. In addition to conducting these measurements, the specific objectives are: 1) Calculate tracer ages and identify the relative extent of ventilation and dilution of thermocline, intermediate and bottom waters within which TEIs reside - from the end member sources to downstream locations as waters age, and put the GEOTRACES data in the historical context of changing ventilation due to natural and anthropogenic climate change. The age data will be available for PIs to evaluate how scavenging and regeneration are affected as TEIs are transported downstream. 2) Using tracer ages, calculate rates of biochemically important processes - e.g., apparent oxygen utilization rates, and help to distinguish between contributions from physical and biochemical processes across the different circulation regimes. Tracer ages will be calculated, from the ratio of SF6 to CFCs, and for oldest waters the ratio of CFCs to each other. The most robust tracer combination for ocean processes on time scales of less than 35 years is obtained using the SF6/CFC ratios.

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.

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.