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Vol. 34 No. 4
July-August 2012

The Project Place | Information about new, current, and complete IUPAC projects and related initiatives.
See also www.iupac.org/projects

Metal-Binding Organic Ligands

The trace metals iron (Fe), copper (Cu), nickel (Ni), cobalt (Co), cadmium (Cd), and zinc (Zn) are essential micronutrients to marine phytoplankton, controlling primary productivity in up to half of the open ocean, from tropical to polar regions. Consequently, these metals exert a major influence on the global carbon cycle and play a key role in regulating climate. However, the availability of these metals to the biota is governed by speciation, whereby trace metals are bound by organic ligands that may reduce or enhance metal bioavailability, depending on the metal and the resulting metal-ligand complex. Organic ligands are defined as molecules that can bind to, and form a stable complex with, trace metals in the aquatic dissolved (typically <0.2 µm) phase. Electrochemical techniques have shown that trace metals in seawater are overwhelming bound (up to 99.999%) by organic ligands, and that these ligands are ubiquitous in the ocean. More recently, organic geochemical techniques have shown that at least some Fe-binding ligands are produced by the biota. Over the past three decades, major advances in analytical techniques have led to a consensus on accuracy and precision for total dissolved trace metal analyses and dramatically improved our knowledge on the global and regional distributions of trace metals. In contrast, our understanding of trace metal-binding ligands and their pivotal biogeochemical functions remains at a comparatively early stage. To date, we know little about the composition, distributions, and provenance of metal-binding ligands, which is hindering further advances in the field of trace metal biogeochemistry.

By combining the expertise and analytical advances of trace metal biogeochemists, organic geochemists, and modelers, this community is poised to make a significant step towards assessing metal-binding ligands in the ocean and defining new research directions for metal speciation. This will enable trace metal speciation data to be better incorporated into global climate models to predict how organic complexation, and consequently trace metal cycles, will respond to projected changes in ocean acidification and oceanic oxygen minimum zones. To facilitate this effort, an ICSU Scientific Committee on Oceanic Research (SCOR) Working Group 139: Organic Ligands—A Key Control on Trace Metal Biogeochemistry was formed.

This SCOR Working Group met for the first time in February 2012 following the ASLO Ocean Sciences Meeting in Salt Lake City, Utah, to approve and commence on the Working Group's terms of reference. Members of Working Group 139, comprised of trace metal biogeochemists, organic geochemists, and biogeochemical modelers, have identified three overarching goals to be advanced over a four-year term:

  1. promote improvements in quality, accessibility, and development of analytical methodologies for characterizing metal-binding ligands in seawater
  2. characterize which components of the dissolved organic matter pool make a significant contribution to biogeochemistry of trace metals in the oceans
  3. identify the role of ligands in microbial ecology and marine biogeochemical cycles

Following the first meeting, the Working Group has begun working towards building a database to link trace metal biogeochemistry and organic geochemistry data at established time-series stations, advancing the ligand intercalibration program initiated by GEOTRACES, and summarizing methodological approaches to assess metal-binding ligands in seawater. The next SCOR Working Group 139 meeting will be on 16 February 2013 preceding the ASLO Aquatic Sciences Meeting in New Orleans, Louisiana. We have proposed a scientific session for the Aquatic Science meeting to complement the SCOR Working Group 139 goals.

Anyone interested is welcome to join our e-mail list by contacting the co-chairs and to participate in the proposed scientific session. Information, progress, and updates on future meetings, database development, and upcoming intercalibration exercises may be found via the SCOR website.

www.scor-int.org/Working_Groups/wg139.htm

For more information, contact Kristen N. Buck <kristen.buck@bios.edu>, Bermuda Institute of Ocean Sciences, Bermuda; Maeve C. Lohan <maeve.lohan@plymouth.ac.uk>, University of Plymouth, United Kingdom; or Sylvia G. Sander <sylvias@chemistry.otago.ac.nz>, University of Otago, New Zealand.


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