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

Concentrations of dissolved micronutrient trace metals (Fe, Zn, Ni, Cu, Cd, Pb, Mn) in seawater, sea ice, and melt ponds collected on the US GEOTRACES Arctic cruise (HLY1502, GN01) from August to October 2015.

These data have been published in the following:
Marsay et al., 2018 – Melt pond metal concentrations
Kadko et al., 2019 – Surface seawater metal concentrations
Jensen et al., 2019 – Dissolved Zn seawater concentrations
Zhang et al., 2019 – Dissolved Cd seawater concentrations
Charette et al., 2020 – Upper ocean dissolved metal concentrations
Jensen, 2020 (PhD Dissertation)

All trace metal-clean seawater samples in this dataset were collected following the prescribed US GEOTRACES protocol ("GEOTRACES cookbook": for more information see (Cutter et al., 2010; Cutter and Bruland, 2012)). Briefly, 24 Teflon-coated, acid-cleaned and preconditioned GO-FLO bottles were deployed on an epoxy-coated aluminum rosette and were tripped on ascent at 3 m/min. Once on deck, bottles were immediately capped with plastic shower caps on both ends to reduce contamination and subsequently kept in a clean sampling van under positive-pressure, HEPA-filtered air. All handling and subsampling was performed exclusively by designated, trace metal-clean personnel to preserve homogeneity and further reduce contamination.

During sampling for the GO-Flo samples, salinity and nutrient (unfiltered) samples were taken first, and then all Go-Flo bottles were pressurized to ~0.7 atm with HEPA-filtered air. Each bottle was fitted with an acid-cleaned and seawater-preconditioned 0.2 um AcroPak-200 capsule filter (Pall), and at least 500 mL was passed through each filter to rinse. Samples were collected in acid-cleaned (hydrochloric acid, 1 M (Fitzsimmons and Boyle, 2012)) LDPE bottles (Nalgene) after three 10% rinses of the bottle, cap, and threads and filled to the shoulder or as volume allowed.

In the absence of sea ice, surface samples were collected in trace metal clean fashion by taking a small boat upstream of the ship. The small boat was pointed into the oncoming current to sample "uncontaminated water" as it passed the boat, and a trained trace metal personnel wearing trace metal clean gloves and plastic sleeves submerged an acid-cleaned carboy under the water surface from the bow of the boat, always keeping the carboy pointed into the oncoming water. The carboy was immediately capped and bagged for transit back to the ship, where it was immediately filtered (0.2 um, Acropak-200) and sub-sampled into individual bottles, including our acid-clean 250 mL LDPE bottles.

A small subset of samples from designated "ice stations" (Stations 31, 33, 39, 43) were collected under the ice (approx. 1, 5, and 20 m) after the ice was drilled with a polypropylene/titanium trace metal coring system. Sampling was done using a polypropylene, battery-powered motor centrifugal pump with ½ inch FEP-lined Tygon tubing. Samples were collected and filtered (0.2 um, Acropak-200) into a 25 L acid-cleaned carboy and then sub-sampled back on the ship, including into our acid-clean 250 mL LDPE bottles, within 3 hours of collection.

At these same "ice stations", melt pond samples were collected (Marsay et al., 2018) by clearing surface snow with an acid-cleaned polyethylene shovel and then using a polyethylene/titanium trace metal coring system to drill through the upper ice. Melt pond water was pumped using a battery-powered polyethylene pump through pre-cleaned C-flex tubing into a pre-cleaned LDPE carboy. The melt pond sample in this carboy was filtered and sub-sampled into individual bottles, including our acid-clean 250 mL LDPE bottles, within 3 hours of collection.

Subsequently, all samples were acidified under clean air conditions to pH~2 with 0.012 M HCl (Optima, Fisher Scientific) within 1 week of sample collection and stored at room temperature until analyzed.

At least 9 months after acidification, samples were analyzed for trace metal (Fe, Ni, Cu, Zn, Pb, Cd, Mn) concentrations at Texas A&M University after pre-concentration on a SeaFAST-pico system (Elemental Scientific Inc.). This method follows a modified version of Lagerström et al. (2013) and is described completely for all elements in Jensen et al. (2020). Briefly, 10 mL of acidified seawater sample was weighed and then spiked with an isotope mixture containing 57Fe, 62Ni, 65Cu, 68Zn, 206Pb, and 111Cd. The mixture was then automatically loaded into the SeaFAST system. Monoisotopic metals such as Mn were measured via a 6-point standard curve using standards made up in low-metal seawater (maintained in-house) such that Mn concentrations spanned 0 to 10 nmol/kg; these standard curves were each run through the SeaFAST twice (once to start and once to end each run) as samples. The SeaFAST method buffers the acidified (pH~2) sample with a ~5.90 N ammonium acetate buffer (Optima, Fisher Scientific) to pH ~6.5 and loads the buffered mixture onto a pre-cleaned column containing Nobias PA1 resin (Sohrin et al., 2008). Each sample is then back-eluted with a solution of 10% (v/v) nitric acid and 1 ppb In (Optima, Fisher Scientific) to yield 400 uL, representing a 25-fold pre-concentration of each trace metal. Within days, each eluent is analyzed in low (204Pb, 206Pb, and 111Cd, 114Cd, 115In) and medium resolution (55Mn, 56Fe, 57Fe, 60Ni, 62Ni, 63Cu, 65Cu, 66Zn, 68Zn, 115In) on a Thermo Element XR high resolution ICP-MS in the Ken Williams Radiogenic Facility in the College of Geosciences at Texas A&M University.

Each sample run included ~80 aliquots from the SeaFAST. Every 10 SeaFAST samples on the XR, pure 10% (v/v) nitric with 1 ppb of 115In was run to extract a potential instrument blank coming from the instrument itself. Prior to running on the ICP-MS, the machine was “cleaned” with this mixture as a precaution against contamination from other samples, in addition to using a separate set of cones, nebulizer, spray chamber, and sample probe for SeaFAST samples only.

Data Processing:
The raw counts from the HR-ICP-MS analyses were first corrected for any instrument blank derived from the 10% nitric acid and In solution repeatedly analyzed during the instrumental analyses. Following this, each sample was corrected for machine drift and variation in instrumental sensitivity during analysis using the added 115In as well as instrument mass bias using elemental standards for Fe, Zn, Ni, Cu, Pb, and Cd. Subsequently, all counts for isotope spiked elements were converted to concentration in nmol/kg based on the weight of the sample and known concentrations of the added isotope spike mixture. The counts for the monoisotopic elements were converted to concentration units using the matrix-matched standard curves, which were run through the SeaFAST themselves as samples. It should be noted that all Cd concentrations are reported based on the 114/111Cd ratio.

For every 40 seawater samples at least 24 "Procedure blanks" were included throughout the run (every 10 seawater samples). These process blanks consisted of freshly acidified milli-Q (MQ) water spiked with a diluted version of the isotope spike mixture. Each blank was processed identically to a sample in an attempt to account for contamination coming from solutions (buffer, eluent) used or the SeaFAST itself. The MQ water is typically collected from various supplies at Texas A&M to ensure that the "procedure blank" is not derived from the MQ water itself. After conversion to concentration units, the most consistent procedure blank values for each metal are used to subtract an average procedure blank from all sample concentrations determined during that run. Each run, an internal standard was analyzed six times and an external standard (such as SAFe water) was analyzed two times as a "check" of our long-term precision and accuracy.

Quality Control:
For detection limits, accuracy, and precision information, refer to the Supplemental File Detection_Limits_Accuracy_Precision_817259 (PDF)

Quality Flags:
Data were flagged using the SeaDataNet quality flag scheme. For more information on SeaDataNet flags, see: https://www.geotraces.org/geotraces-quality-flag-policy/ and https://www.seadatanet.org/Standards/Data-Quality-Control

SeaDataNet quality flag definitions:
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.

BCO-DMO Processing:
- renamed fields;
- added date/time columns in ISO8601 format;
- 2021-04-15 (v2): made the following corrections:
changed Event_ID to 6449 for Sample_ID numbers 12147, 12151, 12155, and 12161;
added Start_Time_UTC, Start_Latitude, and Start_Longitude to Event_ID 6405 (these values were obtained from dataset https://www.bco-dmo.org/dataset/762056)

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 the concentrations of iron, manganese, zinc, copper, cadmium, and nickel from a variety of seawater and ice samples in the Western Arctic Ocean. These are commonly referred to as 'micronutrients' because they are present in the ocean in extremely low concentrations and because they are essential for marine organisms. 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. The six trace elements to be measured in this study are arguably the most important bioactive trace elements in the oceans, and their measurement will provide key information on biological and physical processes in the Arctic. This project will be carried out under the direction of a postdoctoral researcher, providing a unique professional development opportunity for an early career scientist. In addition, the research will involve the training of an undergraduate researcher, and provide public outreach opportunities to K-12 teachers and students, and indigenous populations in Alaska.

The six micronutrients to be measured under this project have all been identified as key trace elements for the GEOTRACES Program. This research will allow rigorous testing of the Arctic physical and biological processes, many of which are already undergoing fundamental changes as a result of climate change, that control the inputs and fate of key micronutrient metals in the Arctic Ocean. Colloidal distributions are specifically targeted in order to derive additional information on the unique physicochemical form and reactivity of distinct dissolved metal pools. The project will also explore the role of melting sea ice in driving near-surface concentrations of these elements by measuring concentrations and size partitioning of these six metals in sea ice, snow, melt ponds, and in the seawater immediately under sea ice. Given that the Arctic is a relatively small basin surrounded by broad continental shelves, sedimentary sources and sinks will also play a major role in controlling the distributions of these elements. Thus, metal concentrations in porewater samples from bottom sediments will also be determined from cores in the Bering and Chukchi Seas, in order to investigate benthic exchanges.

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.