Table of Contents

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

This dataset contains data from samples analyzed at Oregon State University (OSU). Additional dissolved REE data are reported by Lamont-Doherty Earth Observatory (LDEO) in a separate dataset (see 'Related Datasets').

Samples were filtered, acidified, and split at sea. Samples were collected by Niskin bottle. Refer to the cruise report for more information on cruise operations (http://dmoserv3.whoi.edu/data_docs/GEOTRACES/Arctic/ARC01-report.pdf). 

For REE concentrations we removed an aliquot before pH-adjustment of each sample. Sample methodology is modified from the Lab #3 methods in Behrens et al. (2006) using a technique pioneered by Tachikawa et al. (1999). Samples were spiked with a mixed 142Ce, 148Nd, and 176Yb enriched isotope spike blend, and 10 ml of this spiked sample was preconcentrated offline using a SeaFast PICO system (ESI). Resulting solutions were analysed at Oregon State University (Corvallis, OR) using a Thermo X-Series II ICP-MS.

We prepared our 5L split for neodymium isotopic analysis following Shabani et al. (1992). Samples were pH-adjusted to pH ~3.5, then pumped through 300 µl of HDEHP in a C18 cartridge to capture REEs. Rare earth elements were eluted from the cartridge using 6M HCl, then Nd was isolated using sequential chromatographic columns: AG50-X8 (BioRad) and Ln-Spec (Eichrom). Neodymium isotopic measurements were made at Oregon State University using a Nu Plasma 3 multicollector ICP-MS (Nu Instruments).

Problem report: Gaps in Nd isotope data are due to errors made during column chromatography. Where the 2-sigma error of epsilon-Nd is ≥0.7, data is flagged with QV:IODE code 3, questionable/suspect quality.

Neodymium isotope ratios were corrected using JNdi-1 standard for reference (Tanaka et al., 2000). Dissolved concentrations were determined by a combination of isotope dilution and external calibration following methods developed by Tachikawa et al. (1999) and used by Lacan and Jeandel (2001) and Jeandel et al. (2013). Calibration standards were diluted and spiked with a mixed 142Ce, 148Nd, and 176Yb enriched isotope spike blend and were pre-concentrated using the same method as the samples. For Ce the concentration was determined by isotope dilution using 142Ce. For the other REEs we determined the concentrations of Nd and Yb in the samples both by isotope dilution and by external calibration, then used these two results to generate a ratio (spiked value / external calibration value) that we applied to the other REEs. Precision was determined by repeated measurements of two in-house seawater samples, one from Bransfeld Strait (~1100m depth) and one from nearshore California (~surface depth). Reported values here of Ce, Nd, and Yb are calculated by isotope dilution, and for other REEs by external calibration modified by the ratio described above.

Description from NSF award abstract:
In pursuit of its goal "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", in 2015 the International GEOTRACES Program will embark on several years of research in the Arctic Ocean. In a region where climate warming and general environmental change are occurring at amazing speed, research such as this is important for understanding the current state of Arctic Ocean geochemistry and for developing predictive capability as the regional ecosystem continues to warm and influence global oceanic and climatic conditions. The three investigators funded on this award, will manage a large team of U.S.scientists who will compete through the regular NSF proposal process to contribute their own unique expertise in marine trace metal, isotopic, and carbon cycle geochemistry to the U.S. effort. The three managers will be responsible for arranging and overseeing at-sea technical services such as hydrographic measurements, nutrient analyses, and around-the-clock management of on-deck sampling activites upon which all participants depend, and for organizing all pre- and post-cruise technical support and scientific meetings. The management team will also lead educational outreach activities for the general public in Nome and Barrow, Alaska, to explain the significance of the study to these communities and to learn from residents' insights on observed changes in the marine system. The project itself will provide for the support and training of a number of pre-doctoral students and post-doctoral researchers. Inasmuch as the Arctic Ocean is an epicenter of global climate change, findings of this study are expected to advance present capability to forecast changes in regional and globlal ecosystem and climate system functioning.

As the United States' contribution to the International GEOTRACES Arctic Ocean initiative, this project will be part of an ongoing multi-national effort to further scientific knowledge about trace elements and isotopes in the world ocean. This U.S. expedition will focus on the western Arctic Ocean in the boreal summer of 2015. The scientific team will consist of the management team funded through this award plus a team of scientists from U.S. academic institutions who will have successfully competed for and received NSF funds for specific science projects in time to participate in the final stages of cruise planning. The cruise track segments will include the Bering Strait, Chukchi shelf, and the deep Canada Basin. Several stations will be designated as so-called super stations for intense study of atmospheric aerosols, sea ice, and sediment chemistry as well as water-column processes. In total, the set of coordinated international expeditions will involve the deployment of ice-capable research ships from 6 nations (US, Canada, Germany, Sweden, UK, and Russia) across different parts of the Arctic Ocean, and application of state-of-the-art methods to unravel the complex dynamics of trace metals and isotopes that are important as oceanographic and biogeochemical tracers in the sea.

NSF Award Abstract:
In this project, investigators participating in the 2015 U.S. GEOTRACES Arctic expedition will measure neodymium isotopes and rare earth elements in seawater, sediment, and particulates collected from the western Arctic Ocean. In common with other national initiatives in the International GEOTRACES Program, the goals of the U.S. Arctic expedition are 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. Some trace elements are essential to life, others are known biological toxins, and still others are important because they can be used as tracers of a variety of physical, chemical, and biological processes in the sea. Neodymium and rare earth elements are oceanographic tracers, and data from this research will provide benchmarks for other trace element and isotope studies to better understand their cycles and how future environmental changes will impact this important ocean basin. The project will support the training of undergraduate, graduate, and post-doctoral researchers, and results will be disseminated via public outreach activities.

Neodymium (Nd) isotopes are tracers of water mass sources, transport and mixing, and rare earth elements (REEs) show systematic fractionations during environmental processes. Together they provide a powerful tool for analyzing provenances and processes in the oceans that reflect the changing environmental controls on the distribution of trace elements and their isotopes (TEIs). Inherent logistical difficulties make the Arctic Ocean especially scarce in TEI data (including Nd isotopes and REE concentrations), which hinders understanding and application of these tracers. In this study, researchers will examine Nd and REE concentrations in seawater, sediment, and particulate samples collected in the western Arctic Ocean, with the aim of (1) assessing Arctic circulation and water mass mixing in light of Nd isotopes and REEs; (2) attempting to quantify particle-dissolved exchanges of TEIs and; (3) using Nd isotopes and REEs to characterize the sources, sinks and exchanges of TEIs. It is expected that through improved understanding of the Nd isotope and REEs tracers, scientists will be able to relate these findings to other TEIs and to the broader understanding of Arctic oceanographic change in the past, present, and future.

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.