Table of Contents

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

This dataset includes particulate total mercury and particulate monomethylmercury concentrations from the Western Arctic Ocean, which were sampled as part of the 2015 US GEOTRACES Cruise (GN01; HLY1502). Samples were collected with McLane pumps, size fractionated between 1 and 51 um.

Status note (2020-10-28): This dataset has been replaced. Use the following dataset instead: https://www.bco-dmo.org/dataset/827530

Sample collection with in-situ pumps is outlined in Bishop et al. 2012.

Particulate samples were frozen and transported to Wright State University (Dayton, OH) where they were analyzed within 6 months of collection. Filter punches were digested in acid-cleaned polypropylene containers with 8 mL of 2N HNO₃ (Baker Instra-Analyzed).  After analysis of MMHg, an aliquot of digestate was oxidized with BrCl solution for total Hg determination, according to Hammerschmidt & Fitzgerald (2006). All analyzes were performed on Tekran Model 2500 CVAFS Mercury Detector.

Particulate HgT analysis was done according to Fitzgerald & Gill (1979), Bloom & Fitzgerald (1988), and Bloom (1989). The method detection limit was 0.75 pmol/kg, and procedural duplicates averaged 7 ± 6 RPD (n = 16).

Particulate MMHg was analyzed according to Tseng et al. (2004). The detection limit for the method was 0.075 pmol/kg.

While at sea, variable gas pressure in the gas chromatograph caused irregular MMHg peak retention times, making it indecipherable from the inorganic Hg peak. Accordingly, seawater samples ranging from 0.25 to 2 L, were acidified to 1% with sulfuric acid and shipped frozen to Wright State University for analysis.

WOCE Quality Flags:
2 – Ok,
3 – Questionable,
4 – Bad Analysis,
5 – Sample lost,
6 – Mean of replicates,
9 – Sample was not collected for Hg analysis.

"nd" indicates no data.
"bdl" indicates below detection limit.

BCO-DMO Processing:
- separated cruise column into two: cruise_name and cruise_id;
- modified parameter names; applied GEOTRACES names provided by submitter;
- corrected HLY cruise ID number (they were incrementing by one for each row). - joined the following columns from HLY1502 event log, based on the GEOTRC_SAMPNO: GETORC_EVENTNO, GEOTRC_INSTR, ISO_DATETIME_UTC_START_EVENT, ISO_DATETIME_UTC_END_EVENT, EVENT_LAT, EVENT_LON, CASTNO.
- 30-Oct-2018: removed embargo on dataset.
- 21-Oct-2019: corrected units of measurement for Hg_SPT_CONC_PUMP and HG_MM_SPT_CONC_PUMP in parameter defintions section of metadata. These were previously labeled as picomolar but values are reported in pmol/kg.

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 from Woods Hole Oceanographic Institution and Wright State University participating in the 2015 U.S. GEOTRACES Arctic expedition will measure total mercury and mercury species in seawater, particles, sediments, snow and ice samples to better understand its cycling in the Arctic Ocean. 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. In its methylated form, mercury poses a serious human and ecosystem health threat, and this research will provide important information on the extent and rate of change of mercury in the sensitive Arctic ecosystem. Results from this study will be shared through outreach efforts to middle schools students in the Dayton, Ohio area, and the research will involve training for graduate and undergraduate students.

Mercury is a toxic trace metal that originates from natural and anthropogenic sources, and can enter the oceans through many processes, most importantly atmospheric deposition, riverine discharge, and coastal erosion in the Arctic Ocean. Mercury in the ocean can be transformed into varying species by a variety of abiotic and biotic processes. Its transformation to methylmercury is of primary concern as it can biomagnify in food webs. Wildlife in the Arctic has experienced unprecedented increases of methylmercury in their tissues during the past 200 years. While there has been a great deal of research related to mercury cycling in the Arctic in recent years, there remain large gaps in fundamental understanding, particularly with respect to mercury distributions and speciation. The researchers will 1) measure the concentration of four mercury species in the water column, particles, sediments, snow and sea ice samples, 2) determine the concentration of other related chemical species (thiols and snow/ice bromine), and 3) explore the mercury-related genomics of bacteria in various samples. Results from this work will yield new insights into the extent and rate of change of mercury loadings in the Arctic Ocean.

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.