Final Technical Report: The Effects of Iron Complexing Ligands on the Long Term Ecosystem Response to Iron Enrichment of HNLC waters

• Main Author: Cochlan, William P.
• Other Authors: United States. Department of Energy. Office of Science.
• Format: Report
• Language: English
• Published: San Francisco State University 2008
• Subjects: Efficiency; Monitoring; Pacific Ocean; Diatoms; Carbon Cycle; Ecosystems; Cyanobacteria; Seawater; 54 Environmental Sciences; Iron; Carbon; Availability; Carbon Sequestration; Pacific; Southern Ocean
• Online Access: https://doi.org/10.2172/929692; http://digital.library.unt.edu/ark:/67531/metadc896358/

Substantial increases in the concentrations of the stronger of two Fe(III) complexing organic ligand classes measured during the mesoscale Fe enrichment studies IronEx II and SOIREE appeared to sharply curtailed Fe availability to diatoms and thus limited the efficiency of carbon sequestration to the deep. Detailed observations during IronEx II (equatorial Pacific Ocean) and SOIREE (Southern Ocean –Pacific sector) indicate that the diatoms began re-experiencing Fe stress even though dissolved Fe concentrations remained elevated in the patch. This surprising outcome likely is related to the observed increased concentrations of strong Fe(III)-complexing ligands in seawater. Preliminary findings from other studies indicate that diatoms may not readily obtain Fe from these chemical species whereas Fe bound by strong ligands appears to support growth of cyanobacteria and nanoflagellates. The difficulty in assessing the likelihood of these changes with in-situ mesoscale experiments is the extended monitoring period needed to capture the long-term trajectory of the carbon cycle. A more detailed understanding of Fe complexing ligand effects on long-term ecosystem structure and carbon cycling is essential to ascertain not only the effect of Fe enrichment on short-term carbon sequestration in the oceans, but also the potential effect of Fe enrichment in modifying ecosystem structure and trajectory.