Table of Contents

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

Total dissolved sulfide (TDS) and carbonyl sulfide (OCS) were collected from the Oceanographic Data Facility (ODF) Niskin bottles and the GeoFish and stored in 4 liter (L) polyethylene cubitainers. The cubitainers were rinsed 3 times with the sample before filling hermetically with approximately 1.5 L of seawater sample and stored in a refrigerator until analyzed at sea, within 8 hours of collection using the Radford-Knoery and Cutter (1993) method.

Roughly 100 milliliters (mL) of the seawater sample was used to rinse the gas stripping vessel, and then filled with 300 mL of seawater sample and purged with helium (120 mL/minute) for 2 minutes. After 2 minutes, the cryogenic trap was immersed in liquid nitrogen followed by injecting 1.5 M phosphoric acid and stripped/trapped the gases for 20 minutes before quantifying TDS and OCS using a gas chromatograph coupled with a flame photometric detector.

This method quantifies TDS as free ions and metal-sulfide complexes with detection limits of 0.2 picomoles per liter (pmol/L) for TDS and 1.3 pmol/L for OCS for 300 mL samples (Radford-Knoery and Cutter, 1993). Dissolved sulfide water samples were analyzed primarily in duplicate, occasionally triplicate when time permitted. To ensure accuracy, the H₂S and OCS gases were calibrated using permeation tubes whose permeation rates have been gravimetrically measured for 2 to 4 years. By trapping and measuring known amounts of permeated H₂S and OCS over a range of times, linear calibration curves for each gas were assembled daily and applied to unknown samples.

The output signal from the detector was processed using Agilent’s ChemStation software. The sulfide peaks were manually integrated in the software and converted to a value in pmol S using the slope calculated from the system's calibration immediately before or after processing the samples. The values for TDS and OCS were converted to pmol S/L by accounting for the volume of seawater sample analyzed in the gas stripping vessel (300 mL).

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;
7 = value in excess;
8 = interpolated value;
9 = missing value;
A = value phenomenon uncertain.

- Loaded sheet 1 of original file "RR2214_dataTemplate_TDS-OCS-only.xlsx" into the BCO-DMO system, treating "nd" as a missing data value (missing data values are empty/blank in the final CSV file).
- Renamed columns to comply with BCO-DMO naming conventions.
- Applied find/replace to normalize Start_Date_UTC values: converted dd-mm-yy format to YYYY-mm-dd and dd/mm/YYYY format to YYYY-mm-dd.
- Applied same date normalization to End_Date_UTC; additionally corrected the erroneous value "2022-29-29" to "2022-12-29".
- Combined Start_Date_UTC and Start_Time_UTC into a new ISO 8601 datetime column Start_ISO_DateTime_UTC (format %Y-%m-%dT%H:%M:%SZ, UTC).
- Combined End_Date_UTC and End_Time_UTC into a new ISO 8601 datetime column End_ISO_DateTime_UTC (format %Y-%m-%dT%H:%M:%SZ, UTC).
- Saved the final file as "1001179_v1_gp17-oce_tds_ocs.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:
Trace metals are present at very low parts per trillion concentrations in the ocean but in spite of their scarcity many, like iron and zinc, are essential to the growth of the microscopic plants called phytoplankton. Others, like mercury and arsenic, are toxic. In addition to very low concentrations, the essential or toxic nature of a trace metal also depends on the chemical form of the element – as a free dissolved ion all by itself or as charged ion interacting with other inorganic or organic ions. One of the inorganic ions in seawater that strongly interacts with trace metals is bisulfide, the ionic form of the foul-smelling gas hydrogen sulfide. Its reactivity with metals can be so strong that it forms metal-sulfide particles that sink out and are removed from the water. This research project will study how hydrogen sulfide interacts with trace metals like cadmium, copper, mercury, nickel, and zinc to form dissolved complexes that make these metals less reactive to other ions and phytoplankton, or insoluble particles that remove the metals. The researchers will conduct these studies on an oceanographic expedition from Tahiti to the ice edge around Antarctica to Chile as part of the U.S. GEOTRACES program with many other researchers measuring trace metals from the surface to the ocean bottom. All of this and more will be the subject of a graduate student’s doctoral research. In addition to learning how to work on a major oceanographic expedition and with other researchers, she will communicate her experiences and findings on a blog available to all who follow it. She will also help to create a presentation about her science that will be part of the “Sailing with GEOTRACES” virtual reality experience for schools, libraries/museums, festivals, and public presentations.

The US GEOTRACES GP17-OCE cruise from Tahiti to the Antarctic ice edge to Chile will sample waters with large gradients in phytoplankton biomass and species, macronutrients, and trace metals. With anticipated changes in the concentrations and phases of hydrogen sulfide in the oxic water column, the transect offers an ideal opportunity to quantify the linked cycles of hydrogen sulfide and bioactive metals like cadmium, copper, and zinc, and the toxic element mercury. With an overall goal of quantifying the coupled cycles of trace metals and sulfide in the upper, oxic ocean, our specific research objectives for this research will be: (1) Quantify the sources and sinks of dissolved and particulate sulfide as it pertains to the cycling of key trace metals in order to accurately link their cycles; (2) Establish the conditions under which free sulfide reacts with and precipitates trace metals such as cadmium, copper, and zinc, and quantify this removal term; and (3) Evaluate whether nanoparticulate/colloidal pyrite exists in hydrothermal plumes and its contribution to iron transport relative to colloidal iron oxyhydroxides. A fully integrated set of shipboard measurements, laboratory studies, and data synthesis and speciation modeling are designed to meet these objectives. The approach includes close collaborations with investigations of dissolved and particulate trace metals and their speciation, as well as with those studying mixing processes using a variety of tracers.

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.