GEOTRACES is a newly initiated international oceanographic program to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the oceans and to establish an understanding of the sensitivity of these distributions to changing environmental conditions. During the GEOTRACES cruise to the North Atlantic basin in 2010, a scientist from the Bermuda Institute of Ocean Sciences will focus on characterizing the organic complexation of dissolved iron (Fe) in the water column. Iron is typically >99% complexed by strong organic ligands in the marine environment making these ligands a crucial component of the biogeochemical cycling of this element. The specific goals of the proposed work are the following: (1) determine the distributions of strong Fe-binding organic ligands and the sources of variability in the relationship between strong ligand and dissolved Fe concentrations in the proposed hydrographic regions; (2) inter-compare shipboard and laboratory-based speciation analyses with those of other analysts as well as with published field data; and (3) assess any apparent contributions of aeolian deposition to changes in dissolved Fe-binding organic ligand concentrations in surface waters.
As regards broader impacts, results from this study would provide much-needed field data for future modeling endeavors. The outreach component of the study was truly impressive and includes the production of an radio segment from 'Our Ocean World' that highlight research finding from this study and the collaboration with high school teachers to develop lesson plans containing both hands-on experiments related to the project.
The primary objective of this project was to measure the organic complexation of dissolved iron (Fe) along the U.S. GEOTRACES North Atlantic Section. GEOTRACES is an international program aimed at characterizing the distributions and cycling of key trace elements and isotopes in the oceans. The U.S. GEOTRACES North Atlantic Section was sampled aboard the R/V Knorr over the course of two cruises, the first in October-November 2010 (shortened early due to problems with the ship’s propulsion system), and the second expedition to complete the section in November-December 2011. Dissolved iron (Fe) is an essential element for phytoplankton, limiting the growth of marine phytoplankton in large regions of the ocean and influencing the global carbon cycle. The biogeochemical cycling of this important micronutrient in the oceans remains unclear, though it is well established that nearly all dissolved Fe in seawater is complexed by Fe-binding organic ligands. The distribution of Fe-binding ligands is poorly characterized in the marine environment, and particularly in the deep sea. For this project, the concentrations, conditional stability constants, and overall binding capacity of Fe-binding ligands was determined in 550 full depth water column samples collected along the U.S. GEOTRACES North Atlantic Section. An electrochemical method (competitive ligand exchange- adsorptive cathodic stripping voltammetry) was employed for all measurements, which were conducted in part at sea and otherwise back in the laboratory at the Bermuda Institute of Ocean Sciences (BIOS). These data have been submitted for publication in a peer-reviewed journal and have been made available as a database online. Education, training and outreach activities are an integral component of this project. In addition to submission for publication and for an online database, the results of this project have also been presented to the scientific community at several domestic and international meetings and workshops. Project activities have been shared with the public via weekly free public tours at BIOS, annual participation in public outreach events, local news articles in Bermuda and a radio interview aired to over 500,000 people and archived online as an educational resource. Project activities have contributed to educational resources for course development in an international program for junior scientists in developing nations, in graduate level oceanography courses at the University of South Florida (USF), and in a K-12 teaching curriculum. The project provided training to a high school teacher, an undergraduate intern, and four research technicians; three of these trainees have since been admitted to graduate programs in the U.S. to pursue advanced degrees in ocean sciences.
