Table of Contents

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

Dissolved and labile cobalt from the US GEOTRACES Arctic cruise, HLY1502 (GN01).

Samples were collected using the ODU GEOTRACES Carousel (GT-C), filtered through 0.2 um Acropak filters in the GEOTRACES clean van and immediately refrigerated. Acid-washed 60 mL LDPE bottles were filled entirely, leaving no headspace. Total dissolved cobalt samples were kept at ambient pH, preserved in a heat-sealed bag containing gas absorbing satchels immediately after sample collection and kept at 4 degrees C until analysis upon return to the Woods Hole laboratory. Labile cobalt were kept at ambient pH, and sampled in separate bottles stored in plastic bags without gas absorbing satchels at 4 degrees C.

The carousel was used to collect samples from surface to near bottom waters. Additional samples were collected from a surface pump when sea ice conditions permitted. Pre-conditioned, teflon-coated 12L Go-Flo sampling bottles (General Oceanics, Miami, FL) were deployed on a polyurethane powder-coated aluminum rosette with titanium pilings and pressure housings (Sea-Bird Electronics, Inc., Bellevue, WA) attached to a Kevlar, non-metallic conducting cable. For more information regarding carousel deployment, please refer to the GEOTRACES Cookbook, cited below and located on the GEOTRACES Program website (https://www.geotraces.org/). Following carousel retrieval, Go-Flo bottles were moved to the GEOTRACES Program class-100 trace metal clean van, and pressurized with HEPA filtered air for sampling in accordance with published methods (Cutter and Bruland 2012). Surface pump samples were collected by zodiac, and a trace metal clean peristaltic pump following the GEOTRACES Program Cookbook sampling recommendations, and in accordance with previous collection protocols (Bruland et al. 2005).

Sample storage and reagent bottles were soaked for >1 week in the acidic detergent Citranox, rinsed thoroughly with 18.2 M-Ohm Milli-Q water (Millipore), filled with 10% HCl to soak for 10 days, and rinsed thoroughly with Milli-Q water adjusted to pH 2 with TM-grade HCl. Reagent purification protocols were identical to those previously published (Saito and Moffett 2001).

Concentrations of total dissolved cobalt and labile cobalt were determined using a previously described cathodic stripping voltammetry (CSV) method (Saito and Moffett 2001, Saito et al. 2004). Measurements were made using the Eco-Chemie µAutolabIII systems connected to Metrohm 663 VA Stands equipped with hanging mercury drop electrodes and Teflon sampling cups. Sample preparation was modified slightly to accommodate use of a Metrohm 837 Sample processor, operated with NOVA 1.8 software (Metrohm Autolab B.V.).

For total dissolved cobalt analyses, samples were UV-irradiated for 1 h prior to analysis in a Metrohm 909 UV digester to degrade the organic ligands that bind cobalt, enabling full chelation by the added electroactive ligand, dimethylglyoxime (DMG). 11 ml of sample was pipetted into 15ml polypropylene tubes. Recrystallized DMG (0.1M in methanol) was added to a final concentration of 400 uM and purified N-(2-hydroxyethyl)piperazine-N-(3-propanesulfonic acid) (EPPS) buffer (0.5 M in Milli-Q water) was added to a final concentration of 3.8 mM. Tubes were inverted several times before being placed in the autosampler queue, where 8.5 ml of the mixture was dosed into the teflon analysis cup using a 800 Dosino automated burrette (Metrohm). 1.5 ml of purified sodium nitrite (1.5M in Milli-Q water) was added directly to the Teflon cup using a dedicated 800 Dosino burrette. Once loaded, samples were purged with high purity (>99.99%) N2 for 3 min and cobalt concentrations were determined by standard addition, with triplicate measurement of the sample followed by four 25 pM cobalt additions. 5 nM Co stock was diluted from a certified 1ppm reference (SPEX) and added to the analysis cup via a third Dosino burrette.

For labile cobalt analyses, 11 ml of sample were pipetted into acid washed teflon vials, preconditioned with a small aliquot of sample water. DMG was added to a concentration of 400 uM and allowed to equilibrate for 8-16hr in the dark prior to analysis (Saito et al. 2004). EPPS was added just prior to measurement using the same standard addition protocol described above. Previously, we determined that natural cobalt ligands in seawater have a conditional stability constant of >10^16.8 (Saito et al. 2005). This suggests that the cobalt is very strongly bound to ligands. Thus, we define labile cobalt as the fraction of total dissolved cobalt that is either bound to weak organic and inorganic ligands in seawater or present as free Co(II), and is then exchangeable with the complexing agent (DMG) used for analysis (Saito et al. 2004, Saito et al. 2005). The difference between the total dissolved cobalt and the labile cobalt can then be used as an estimation of the strong cobalt ligand concentration. The same electrode was used for both total and labile analyses. Before transitioning from labile analyses to total analyses, the autosampler tubing and Teflon cup were rinsed with Milli-Q water and pH2 HCl in Milli-Q water.

The analytical blank was determined by analyzing seawater that had been UV-irradiated for 1 h, equilibrated overnight with prepared Chelex 100 resin beads (Bio-Rad), and UV-irradiated a second time to degrade any leached synthetic ligands. For in lab analyses, mean blank was 2.5 +/- 0.7 pM (n=19), and the detection limit was 2.2 pM.

Intercalibration: GEOTRACES standard seawater and internal standard lab seawater were analyzed periodically. A large batch of UV oligotrophic seawater was generated prior to sample analyses and used as a primary standard during measurements. This standard seawater was run along with each sample batch, as were blanks, and values were consistent for the duration of analyses. Our laboratory has participated in the GEOTRACES intercalibration effort using this electrochemical Co method. Acidified standards were neutralized with concentrated ammonium hydroxide (Seastar), mixing the entire sample between drops, prior to UV digestion. We report our laboratory values for the GEOTRACES and SAFe standard analyses using this electrochemical method to be: SAFe D1 = 47.9 +/- 2.1 (n=3), SAFe D2 = 45.2 +/- 2.1 (n=3), GEOTRACES GSP = 2.4 +/- 1.8 (n=3), GEOTRACES GSC = 77.9 +/- 2.8 (n=3). These results are in good agreement with those from the GEOTRACES intercalibration effort for Co and demonstrate that the methodologies employed to produce this dataset detect concentrations within the standard deviation of current consensus values for UV irradiated samples, which can be found on the International GEOTRACES Program website (https://www.geotraces.org/).

Peak heights were determined using an in-home Matlab script described thoroughly in Bundy et al. (2020).

Quality flags for both dissolved and labile cobalt:

1 = Good (r^2 of standard additions > 0.95)
2 = Not evaluated, not available, or unknown
3 = Questionable/suspect (r^2 of standard additions < 0.95)
4 = Bad (r^2 of standard additions < 0.90)
9 = Missing data
10 = Below detection limit (Measurement was determined but was found to be below the detection limit)

Problem report:
Some labile samples were kept with the total dissolved cobalt samples by mistake in the bags with the gas absorbing satchels. If the labile sample was mistakenly placed with the totals samples, it was not measured, and is denoted as nd with flag 2 in the data file.

BCO-DMO Processing:
- renamed fields;
- added date/time fields in ISO8601 format;
- 2020-07-07: replaced with GEOTRACES DOoR-formatted/IDP version;
- 2020-10-29: replaced version 2 with version 3, which includes corrections to the depths reported for event number 6009;
- 2021-04-13: displayed the "Co_D_CONC_SUBICE_PUMP" columns, which were previously removed;
- 2021-05-05: replaced entire dataset with new version which contains corrections to the standard deviation columns.
- 2021-05-06: removed "2" in the "SD1_Co_DL_CONC_BOTTLE_8zqltr" column for sample 11882.

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, a group of investigators participating in the 2015 U.S.GEOTRACES Arctic expedition will study the chemistry and regional distribution of seven trace metals in the Arctic Ocean: iron, manganese, zinc, cadmium, copper, nickel, and cobalt. These so-called bioactive metals are of special scientific interest because of their role in multiple biogeochemical processes including biological production of the sea and the planetary cycling of carbon and nitrogen. Like 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. This study in particular would contribute to our understanding of the sources and sinks of these seven bioactive metals as well as examine their interaction with biological processes. The project will focus on two major overarching research questions: (1) What are the sources and sinks for micronutrients and macronutrients in the Arctic? And (2) How does bioactive trace element nutrition influence productivity and species composition in the Arctic, and conversely, how do biological processes influence the cycling of these metals? In terms of broader impacts, the PIs on this project will be actively involved in educational outreach efforts, and the research team itself will include two postdoctoral researchers and a graduate student. The team leaders also plan to publish a children's ocean education book based on the expedition with the aim of generating next-generation excitement about modern ocean science

With regard to technical specifics, the research team will measure the dissolved seawater phases of the bioactive metals Fe, Mn, Zn, Cd, Cu, Ni, and Co, the dissolved stable metal isotopes 56Fe, 66Zn, and 114Cd, and the chemical speciation of Co. The recent development of methods for multi-element and multi-isotope analysis methods, in conjunction with the high-resolution sampling of the GEOTRACES program, make it possible to efficiently produce this dense dataset of metals and metal isotopes. This will be a team-based approach to achieve comprehensive duplication for analysis of the key parameters of dissolved metal concentrations. Each investigator will further conduct specialized additional measurements of metal isotopes and dissolved Co (which has unique analytical challenges) and Co speciation. Interpretation of these rich datasets would will be directed toward determination of sources and sinks as well as their ecological stoichiometry, in collaboration with other U.S.GEOTRACES participants measuring synergistic parameters. Together, this Arctic Ocean bioactive trace metal dataset is expected to provide an important contribution to the understanding of micronutrient roles in Arctic biogeochemical processes. These results should also be highly relevant to research studies of the ancient ocean, in which trace-metal analyses are commonly used to trace a wide variety of processes including paleo-ocean circulation and biological productivity. Finally, understanding the sources and sinks for elements in the modern ocean is key to predicting how the concentrations of bioactive elements might vary in a changing future climate.

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.