As a complementary addition to the U.S. North Atlantic GEOTRACES cruise, a scientist from the University of California, Santa Cruz will provide the core program with an additional 500 surface samples collected using a surface clean fish sampling system. The samples will be analyzed for a suite of key GEOTRACES dissolved trace metals including iron, aluminum, manganese, zinc, cadmium, copper, and non-key elements such as cobalt, nickel, lead and silver. Given the surface samples will be collected from surface waters with a wide range in productivity and export production, as well as contrasting internal, riverine and atmospheric inputs, it will provide the science community with an extensive data set for investigating the sources and removal processes for trace metals from the surface ocean. The availability of this extensive data set also will facilitate collaboration with researchers investigating atmospheric deposition and modeling of transport and cycling of metals in the surface ocean. In addition, data on surface samples collected just prior to arrival on station and upon departure will provide an important check on the data from near surface samples collected with the GEOTRACES carousel sampling system close to the vicinity of the ship. This data will help confirm that all is well with the near surface carousel samples or, if needed, provide a mechanism to correct the near surface data from the carousel sampling system. Besides the surface water samples, an archive of about 528 samples from vertical profiles will be collected from each of the 22 standard or normal GEOTRACES full-depth profiles. Vertical profiles of the trace metals will be analyzed at the 6 "super stations" to facilitate an intercomparison study with other GEOTRACES analysts to ensure quality control between our surface water data and the vertical profile data for the various key GEOTRACES trace metals.
As regards broader impacts, the researcher will continue his trace metal intercalibration efforts by providing the chemical oceanography community with reference samples and baseline data for these samples which benefits not only U.S. scientists but the international community as well. Six months of a postdoc's salary will be supported by this project with the remaining funds provided by the EU GEOTRACES program.
This proposal allowed the Bruland research group at UC Santa Cruz to continue their involvement in the GEOTRACES program during the US North Atlantic zonal section. We were responsible for a number of activities: Geoffrey Smith and the UCSC clean van and clean GeoFish allowed the collection of large volumes of clean surface seawater for a wide variety of investigators. We collected an extensive set of surface seawater samples for the analysis of a large suite of dissolved trace metals. Claire Parker, a graduate student in our research group, is currently finishing these analyses. These samples will provide an extensive set of surface water data over the North Atlantic that will be complementary to the atmospheric aerosol studies and will provide valuable data for modelers. We collected an archive of vertical profile samples in rigorously cleaned, 0.5 liter, low density, polyethylene bottles. This is a library of over 600 samples. We analyzed a suite of metals at the Super Stations to facilitate an intercomparison study with other GEOTRACES analysts. This involved an evaluation of the clean sampling systems developed for the GEOTRACES program and an evaluation of the analytical methods used for the determination of dissolved metals. An example of this is shown in the figure included for dissolved cadmium. This figure shows the excellent agreement between the Netherlands GEOTRACES program and the US GEOTRACES program on a common crossover station – the BATS station near Bermuda. The figure also shows the excellent agreement between three different US labs analyzing Cd (Univ. of South Carolina, John and Conway; Univ. of Miami, Wu; UC Santa Cruz, Middag and Bruland). This intercomparison was to help address quality control issues with the emerging data sets for this global program. We have similar data for a suite of different dissolved trace metals including iron, zinc, lead, manganese, cobalt, nickel, copper and gallium. We have continued to supply a variety of important SAFe and GEOTRACES seawater reference samples to the US and International GEOTRACES community and continually upgrade the consensus values and lists of participating scientists and their methods. This has been invaluable in helping researchers in other countries develop their analytical capabilities in the GEOTRACES program. The proposal provided training for a post doctoral researcher and two graduate students. Dr. Rob Middag, the post doc, is now in a faculty position at the University of Otago in Dunedin, New Zealand. Dondra Biller has a 2012 publication from this research and will be defending her Ph.D. at the end of February 2013. Claire Parker is a second year Ph.D. student in the midst of data analysis.
