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

Seawater samples were collected during the GEOTRACES GP16 cruise on R/V Thomas G. Thompson (TN303) along the East Pacific Zonal Transect in 2013. Five liters (L) of seawater were collected and stored in a cubitainer for each sample. The samples were filtered using 0.2-micrometer (μm) Sartobran cartridges and acidified using ultrapure Seastar hydrochloric acid (HCl) to pH ~ 2 shortly after sampling.

For neodymium (Nd) isotope analysis, rare-earth elements (REEs) were preconcentrated from seawater using C18 cartridges (Waters Corp., Sep-Pak classic, 360-milligrams (mg), 55-105 μm) loaded with complexing agent composed of a mixture of 2-ethylhexyl hydrogen phosphate (HDEHP) and 2-ethylhexyl dihydrogen phosphate (H2MEHP), which was first proposed by Shabani et al. (1992). In this study, we followed the methods by Jeandel et al. (1998), Lacan and Jeandel (2001), and Pahnke et al. (2012). Specifically, C18 cartridges were first cleaned in a 0.5 N HCl bath overnight, passed through 10 milliliters (mL) of 6 N HCl and then flushed with >500 mL of Milli-Q water. Cartridges were stored in Milli-Q water after cleaning. 300 μL of complexing agent HDEHP/H2MEHP was loaded on a clean cartridge for a 5 L sample. Seawater samples were adjusted to pH ≈ 3.5 by adding Optima® ammonium hydroxide before being pumped through the cartridges at 20 mL/minute by a peristaltic pump in the ultra-clean chemistry laboratory at LDEO. Cartridges were then eluted with 10 mL of 0.01 N HCl to remove barium. After barium elution, cartridges were eluted with 35 mL of 6 N HCl at 10 mL/minute by a peristaltic pump to collect REEs. REEs were dried and further purified by TRU-spec column chemistry. Nd fractions were extracted from REEs by LN-spec column chemistry and dried. They were redissolved in 0.3 mL of 3% HNO3 for the Nd isotope analysis.

For REE concentration analysis, a multi-element REE spike enriched in 138La, 142Ce, 145Nd, 149Sm, 153Eu, 155Gd, 161Dy, 167Er, 171Yb, and 176Lu (Wu et al., 2020) was added to each sample (~10 mL). The sample-spike mixture was allowed to equilibrate for at least 24 hours and then was purified and pre-concentrated through the seaFast Automated Preconcentration System for Undiluted Seawater (Elemental Scientific Inc. or ESI, Omaha, Nebraska, USA).

The Nd isotopic composition is expressed as:

εNd = [(¹⁴³Nd/¹⁴⁴Ndsample/¹⁴³Nd/¹⁴⁴NdCHUR) - 1] × 10⁴

This study uses ¹⁴³Nd/¹⁴⁴NdCHUR = 0.512638 (Jacobsen and Wasserburg, 1980).

- Imported original file "DOoR_GEOTRACES GP16_eNd&REEs_LDEO.xlsx" into the BCO-DMO system.
- Flagged '-999' values as missing data values (missing data are blank/empty in the final CSV file).
- Renamed fields to comply with BCO-DMO naming conventions.
- Created the date/time field in ISO 8601 format.
- Removed the end lat/lon and end date/time columns (all empty).
- Saved the final file as "915447_v1_gp16_diss_nd_and_rees_ldeo.csv".

From the NSF Award Abstract
The mission of the International GEOTRACES Program (https://www.geotraces.org/), of which the U.S. chemical oceanography research community is a founding member, is "to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions" (GEOTRACES Science Plan, 2006). In the United States, ocean chemists are currently in the process of organizing a zonal transect in the eastern tropical South Pacific (ETSP) from Peru to Tahiti as the second cruise of the U.S.GEOTRACES Program. This Pacific section includes a large area characterized by high rates of primary production and particle export in the eastern boundary associated with the Peru Upwelling, a large oxygen minimum zone that is a major global sink for fixed nitrogen, and a large hydrothermal plume arising from the East Pacific Rise. This particular section was selected as a result of open planning workshops in 2007 and 2008, with a final recommendation made by the U.S.GEOTRACES Steering Committee in 2009. It is the first part of a two-stage plan that will include a meridional section of the Pacific from Tahiti to Alaska as a subsequent expedition.

This award provides funding for management of the U.S.GEOTRACES Pacific campaign to a team of scientists from the University of Southern California, Old Dominion University, and the Woods Hole Oceanographic Institution. The three co-leaders will provide mission leadership, essential support services, and management structure for acquiring the trace elements and isotopes samples listed as core parameters in the International GEOTRACES Science Plan, plus hydrographic and nutrient data needed by participating investigators. With this support from NSF, the management team will (1) plan and coordinate the 52-day Pacific research cruise described above; (2) obtain representative samples for a wide variety of trace metals of interest using conventional CTD/rosette and GEOTRACES Sampling Systems; (3) acquire conventional JGOFS/WOCE-quality hydrographic data (CTD, transmissometer, fluorometer, oxygen sensor, etc) along with discrete samples for salinity, dissolved oxygen (to 1 uM detection limits), plant pigments, redox tracers such as ammonium and nitrite, 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-type data to the GEOTRACES Data Center (and US data centers); and (6) coordinate cruise communications between all participating investigators, including preparation of a hydrographic report/publication.

Broader Impacts: The project is part of an international collaborative program that has forged strong partnerships in the intercalibration and implementation phases that are unprecedented in chemical oceanography. The science product of these collective missions will enhance our ability to understand how to interpret the chemical composition of the ocean, and interpret how climate change will affect ocean chemistry. Partnerships include contributions to the infrastructure of developing nations with overlapping interests in the study area, in this case Peru. There is a strong educational component to the program, with many Ph.D. students carrying out thesis research within the program.

Figure 1. The 2013 GEOTRACES EPZT Cruise Track. [click on the image to view a larger version]

NSF abstract:
Neodymium isotopes (Nd) and rare earth elements (REE) are recognized by the GEOTRACES program as key trace elements and isotopes (TEIs) because they trace the sources and mixing of water masses. Therefore, transport data generated by Nd measurements will potentially advance our understanding on the dominant processes that drive TEI distribution in the ocean. There is a particular need for Nd measurements in the South Pacific because current observations do not agree with GCM models. Researchers from Columbia University and Oregon State University will analyze seawater, aerosols, water column particulates, and sea-floor sediments for Nd, strontrium, and REE during the upcoming 2013 GEOTRACES cruise. Because of the geographical transect of the GEOTRACES Pacific section cruise, investigators will assess impacts made by a suite of biological, chemical, and physical processes including: boundary exchange, high productivity, surface addition from aerosols, addition to bottom waters from detached nephloid layers, particles from hydrothermal vents, reversible scavenging, and groundwater fluxes. Furthermore, within the Peru-Chili Oxygen Minimum Zone (OMZ), investigators will utilize the TEI cerium to better understand relative effects of lateral and vertical processes. By improving understanding of the distribution of TEIs, results will also enhance biogeochemical models and advance knowledge of climate systems.

Broader Impacts: Research will advance careers of two young scientists, support education and training of Ph.D. and undergraduate students, and provide materials for outreach activities. Additionally, results will be published in scientific journals and all data will be submitted to the Biological and Chemical Oceanography Data Management Office.

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.