Table of Contents

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

Sampling and analytical procedures:
The chemical procedure for the analysis of Po-210 and Pb-210 in aerosols, water samples, snow, ice core, melt ponds and ice-rafted sediments are given in Sampling and Sample-handling Protocols for GEORACES Cruises (known as "Cookbook"): http://geotraces.org/science/intercalibration/222-sampling-and-sample-handling-protocols-for-geotraces-cruises; Baskaran et al., 2013).

Samples for Po-210/Pb-210 analysis were collected from 4 super stations, 3 shelf stations, 1 full station, 1 pacific end member station, 6 ice stations, 2 dirty ice events, and from 14 aerosol deployments. The number of water samples ranged from 16-24 depths for super stations and 3-6 depths for shelf/end member stations. These samples were collected from the ODF rosette and filtered using 0.2um Acropack filters. Two additional filtered water samples were taken from 8L niskins attached atop the multicorer instrument at two separate shelf stations. Four unfiltered water samples were collected for intercalibration between the Wayne State University and Louisiana State Laboratory (collected from 1 full station and 1 super station (original GT 15)). The particulate samples collected by McLane pumps for associated dissolved water samples will be sent to the participating labs for analysis upon completion of the cruise. Samples collected at ice stations included snow, melt pond water, under ice water, and ice cores. All samples were collected unfiltered and subsequently filtered in the onboard lab for analysis of both particulate and dissolved phases. The 2 dirty ice events were conducted between stations using a man basket and each event included a community sample which was divided among other groups. Aerosol deployments were conducted every three or four days, depending on the total run time of the pumps. Dissolved water samples from the shelf stations and 2 of the 4 super stations (original GT13, 15) were acidified and stored for shipment to Dr. Maiti's laboratory where they will be processed. All of the remaining samples were processed onboard by Wayne State personal (Katie Krupp). Dissolved seawater/melted ice station samples were processed by co-precipitation using an iron carrier followed by electroplating to silver planchets. Particle samples and aerosols were leached with acids and plated in the same manner. A known amount of Po-209 spike was added to each sample for determination of Po-210 recovery. These planchets and sample solutions were brought back to Wayne State University for alpha counting and further processing in order to measure Pb-210 and thus determine the Po-210/Pb-210 ratio for each sample collected. In summary, approximately 310 samples were collected for polonium- 210 and lead-210 analysis on the 2015 Arctic GEOTRACES cruise.

Meltpond sampling:
Melt ponds were sampled at Stations 33, 38, 42, 43 and 46. A battery-powered peristaltic pump and silicone tubing were used to fill a carboy for shipboard filtration (Acropak-200, <0.2 um). At each station, the melt ponds were frozen over, so a hole was drilled using the TM-clean corer. Salinity was measured at each melt pond following sampling.

Aerosol sampling:
Aerosol samples were collected over periods of three to five days using five high-volume aerosol
samplers. Three samplers were used to collect aerosols on acid-cleaned Whatman-41 (cellulose) filters for analysis of inorganic trace elements and isotopes (TEIs).

Sea Ice operations:
Snow, ice cores and water under the ice was collected from the six sea ice stations (Table 1).
Ice stations were constricted north of 88.4o N on the northward leg, and north of 82.5o N on the southward leg of the cruise. This narrow latitudinal range resulted from a combination of ice conditions, weather conditions, and available time.

Ice Station Longitude Latitude (samples include snow, ice core, melt ponds and ice-rafted sediment)
Station 31: 183.33W 88.42N
Station 33: 3.529E 89.96N
Station 39: 149.61W 87.78N
Station 42: 150.54W 85.74N
Station 43: 150.00W 85.16N
Station 46: 149.83W 82.49N

Bulk Snow:
Bulk snow for Po-210 and Pb-210 was collected with an acid clean high density polyethylene shovel into a low density polyethylene drum liner. Discrete snow samples were also collected in community provided containers. The bulk snow was melted on board, filtered through a Supor 0.2 um filter membrane and subsampled.

Sea Ice Cores:
Discrete ice cores were collected at all stations. Cores were collected with the Kovaks corer. A total of two Twelve to fifteen cores were taken at each station for a total of 85 sea ice community cores.

Problem report:
We had analyzed a total of 43 water samples, 43 small particle size and 43 large particle size. Out of these, two batches (3 dissolved and 4 particulate (both large and small)) were lost during analysis onboard.

Data processing:
Polonium-210 and Pb-210 data from the alpha spectrometer were analyzed using Excel spreadsheets to calculate their specific activities. Plots have been made using Kaleidagraph software.

Data quality flags:
SeaDataNet data quality flags have been assigned to these data. More information is available from GEOTRACES at http://www.geotraces.org/library-88/geotraces-policies/1577-geotraces-quality-flag-policy and from SeaDataNet at https://www.seadatanet.org/Standards/Data-Quality-Control. In summary:
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 (BDL)
7 = value in excess
8 = interpolated value
9 = missing value

BCO-DMO Processing:
- formatted dates as yyyy-mm-dd;
- added a column for data/sample type;
- replaced 'N/A' and 'NM' with 'nd' (no data, not measured);
- modified column names.
Version history:
2021-07-08 (v2; current) - made corrections to parameter names ("ICE_D_CONC_GRAB" changed to "D_CONC_SUBICE_PUMP").
 2020-02-25 (v1) - version 1 published.

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 team of investigators participating in the 2015 U.S. Arctic GEOTRACES expedition will study the distribution of the naturally-occurring radioactive isotopes lead-210 and polonium-210 in the western and central Arctic Ocean. These measurements are expected to be very useful in helping to meet the goals of the U.S. Arctic GEOTRACES expedition: namely, to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes (TEIs) 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. A primary source of lead-210 to the oceans is from the atmosphere, where it is produced from the decay of radon-222. In the oceans, it decays to polonium-210. The half-lives of polonium-210 (138 days) and lead-210 (22.3 years) provide "natural clocks" with which to investigate processes such as the sorption of elements on to sinking particles, and the transport of elements between the ocean margins and deep basins.

The lead investigator proposes to concentrate sampling and investigate processes at three "interfaces:" the air-sea-ice interface at the surface, the interface between biologically produced particles and water, and the interface between non-biological particles and water. The investigator proposes the following three hypotheses: 1) At the air-sea interface, the polonium-210/lead-210 ratios can be used to "age date" the sea ice (and sediments contained within the ice). 2) At the biotic-water interface, different biogenic particle types encountered in the upper waters will affect the fractionation and remineralization depths of polonium-210 and lead-210. 3) At the particle-water interface, layers of resuspended sediments in the water column will be zones of enhanced polonium and lead scavenging from the surrounding waters. These processes are important for understanding the distributions of other key particle-reactive trace elements such as iron, lead, and manganese. To test these hypotheses, the investigator will sample and analyze about four hundred dissolved and particulate (large and small) samples, 10 multi-year ice cores, ice-rafted sediments, and water from melt ponds for polonium-210 and lead-210 along the GEOTRACES Western Arctic section. About half of the samples will be focused at the four designated "super stations", with half of these in the highly dynamic upper water column and the other half near the sea floor where resuspension of bottom sediments can affect element cycling. The depths will be chosen according to regional atmospheric input, ecosystems, and coordinated sampling with groups measuring other trace elements and isotopes. The remainder of the samples will be ice cores, water from melt ponds, ice-rafted sediments in sea ice, and atmospheric aerosol samples. The proposed work will be closely coordinated with other GEOTRACES. The broader impacts are closely linked to the GEOTRACES program as a whole to enhance (1) research infrastructure by providing a broad array of polonium-210 and lead-210 data useful for biogeochemical scavenging models, (2) education by mentoring graduate and undergraduates, teaching by example
from proposed research, (3) participation of under-represented students careers in the geosciences, (4) research training of graduates in marine radiochemistry, and 5) broad dissemination of results through publications, presentations, and on dedicated public Wayne State University websites (www.clas.wayne.edu) and at GEOTRACES (www.geotraces.org).

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.