Table of Contents

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

Trace element concentrations in particles collected with GO-Flo bottles and analyzed with ICP-MS. Concentrations of labile and total metal fractions are reported. Samples were collected during the U.S. Arctic GEOTRACES cruise aboard USCGC Healy (GN01; HLY1502) from August to October 2015.

Supor PES filters (25 mm or 47 mm diameters, 0.45 µm pore size) were acid-washed in 10% HCl and soaked repeatedly in fresh baths of ultrahigh purity (UHP) water, until the pH of the resulting rinse water was circumneutral. Particulate samples were collected directly from the GO-Flo sampling bottles (pressurized (<8 psi) with filtered air), drawing ~7 L of seawater over the filters loaded into Swinnex or Advantec cartridges, and stored frozen in new polystyrene petri dishes.

Before processing and analysis, filters were divided into halves: one half for Total digestion (total element concentrations) and one half for Labile digestion (using the Berger et al. (2008) method). Digest solutions (Total and Labile) included a 10 ppb In spike to correct for instrumental drift.

Total digestion: Filters were digested in 15-mL PFA digestion vials (Savillex), extensively cleaned using HNO₃, HCl, and trace HF acids (trace metal grade or better). Digestions were performed on enclosed Teflon-coated hotplates ("flowboxes") under double HEPA filtered air (effectively Class-1), inside a Class-1000 clean room. The total digestion procedure involved a two-step digestion, modified from Ohnemus et al. (2014). During the first digestion step, filter halves were submerged in 4 mL of a mixture of 4 M each of HNO₃, HCl, and HF acids (all Optima or double-distilled). Samples were capped and heated for 3 hours at 100-120°C in the flowbox. Each digest solution was then carefully decanted into a second PFA vial, the original vial and filter rinsed twice with 1.5 mL of ultrahigh purity (UHP) water, and the UHP water rinses transferred to the second vial while retaining the filter in the original vial. The digest solution in the second vial was then taken to dryness (uncapped) in the flowbox, by heating overnight at 100-120°C. During the second digestion step, 20 µL of concentrated H₂SO₄(Optima), 20 µL of H₂O₂ (Optima), and 2 mL of 8 M HNO₃ Optima or double-distilled) were added to the digest residue to breakdown any PES filter fragments, and the vials heated (capped) at 150°C for 30 minutes. The vials were uncapped and taken to dryness at 210-230°C. The final digest residue was redissolved in 4 mL of 0.32 M HNO₃(Optima or double-distilled) and stored in acid-washed 5 mL cryovials until analysis.

Labile digestion: Filters were digested in rigorously cleaned 22-mL PFA digestions vials (Savillex). All digestion steps were performed in a Class-100 clean room using standard clean techniques. Filters were digested in a solution of 25% Optima-grade acetic acid and 0.02 M hydroxylamine hydrochloride following the protocol of Berger et al. (2008). One milliliter of this solution was added to the filter stored in a 1.7-mL polypropylene vial. The solution was heated to 95°C in a water bath for 10 minutes and then allowed to cool to room temperature. The filter was in contact with the acetic acid leach for a total of two hours. The filter was removed to an acid-cleaned PFA bomb and the acetic acid/hydroxylamine leachate was centrifuged at 14,000 rpm for 10 minutes to sediment all particles. Without disturbing particles on the bottom of the tube, approximately 0.8 mL of leachate was transferred into a 7-mL PFA digestion vial. Optima-grade HNO₃ was added (100 µL) to the 7-mL digestion vial, which was then heated uncapped at 110ºC to near dryness. Vial contents were redissolved with 2% HNO₃ (Optima grade).

Process blanks and reference materials were digested alongside samples for both chemical treatments. All samples were analyzed at NHMFL/FSU by HR-ICP-MS in both Low and Medium Resolution modes. Concentrations were quantified by multi-element external calibration (seven standards, up to 500 ppb), and drift corrected using a 10 ppb In spike added to each sample.

Quality Flags: 
Particulate data are flagged with the following:
1: Good data, passed QC;
2: Probably good, but no QC;
3: Questionable; value is oceanographically inconsistent based on adjacent depths and/or comparison of leach vs total;
4: Bad;
6: Below detection limit;
9: Missing.

BTLNBR are flagged with the following:
0:  Not sure how to QF this comment;
1:  Bottle information unavailable;
2:  No problems noted;
3:  Leaking;
4:  Did not trip correctly;
5:  Not reported;
6:  Significant discrepancy in measured values between Gerard and Niskin bottles;
7:  Unknown problem;
8:  Pair did not trip correctly. Note that the Niskin bottle can trip at an unplanned depth while the Gerard trips correctly and vice versa;
9:  Samples not drawn from this bottle.

QC: Refer to the GN01 Bottle Particles CRM and blanks Supplement File: "GTArc_metadata_CRM_and_blanks_FINAL.xlsx"

Note: Portions of these data were published in Marsay et al. (2018), Tables 3 and 6, Figure 7.

BCO-DMO Processing:
- modified parameter names (replaced spaces with underscores; labeled flag columns as such; renamed "sample number" to "GEOTRC_SAMPNO");
- filled blank cells (missing data) with "nd"; replaced "NA" with "nd".
- 02-July-2019: replaced version 1 of data with version 2 (GEOTRACES parameter names & units applied; additional metadata columns added)

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:
As part of this project, two investigators will participate in the 2015 U.S. GEOTRACES Arctic expedition to determine the trace element composition of different suspended particles in the water column of the Arctic Ocean to identify the sources and scavenging capabilities of these particles. In common with other multinational 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. This team of trace element scientists will focus on the measurement of particulate trace elements, which will enable scientists to better estimate the sources of particulate metals to the Arctic Ocean and to better understand their contribution to biological processes. This project will also provide educational opportunities for undergraduate students, K-12 teachers, and the general public.

Particulate trace element distributions, sources, sinks and cycling are predicted to be controlled by physical, biological, anthropogenic and geochemical processes in the Arctic. Furthermore, many trace elements are required nutrients for marine phytoplankton, playing a key role in oceanic primary productivity. However, few integrated oceanographic studies have been conducted to specifically investigate these relationships in this region, despite the changing conditions and global significance of the Arctic. This project will significantly advance understanding of the complete geochemical cycles of a number of trace elements in the Arctic Ocean basin by measuring the concentrations of particulate trace elements in bulk particles collected through the water column and in sediments, as well as in phytoplankton from the upper water column. These measurements will enable scientists to constrain the inputs of particulate elements from rivers, shelves and ice, and to assess the removal of dissolved trace elements via passive scavenging and biological uptake.

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.