Program
 
Special Session 1: Ecosystem under multiple stressors
 

 
 
1030
Ocean acidification and iron availability: a natural multiple stressor experiment in iron limited upwelling waters
Wednesday 11th @ 1030-1047
Multi-function Hall
Mark L. Wells* , University of Maine, Orono, Maine, USA
Charles G. Trick, Western, London, Ontario, Canada
Vera L. Trainer, NOAA Northwest Fisheries Science Center, Seattle, Washington, USA
William P. Cochlan, Romberg Tiburon Center for Environmental Studies, Tiburon, California, USA
Christopher Ikeda, Romberg Tiburon Center for Environmental Studies, Tiburon, California, USA
Kathy Thornton, University of Maine, Walpole, Maine, USA
Brian Bill, NOAA Northwest Fisheries Science Center, Seattle, Washington, USA
Presenter Email: mlwells@maine.edu
The dissolved speciation of Fe in seawater is strongly influenced by organic complexation. Theoretical and experimental evidence suggests that ocean acidification will decrease the availability of Fe to phytoplankton. Eastern boundary coastal upwelling systems, sites already experiencing ephemeral low pH conditions, will become sites of extreme ocean acidification by the end of the century. We investigated the effects of ocean acidification on ambient phytoplankton production and community composition in the coastal California upwelling system using deckboard continuous (ECOSTAT) cultures. The natural population cultures were maintained at pH 8.1 and 7.8, with and without Fe amendments, by adjustment of the feedwater inflows. The findings clearly show that chlorophyll biomass increased with lowered pH in both ambient and Fe amended cultures, counter to previous expectations. Increasing the dilution rate from 0.45 d-1 to 0.65 d-1 did not alter this finding. Photosynthetic efficiencies, in contrast, were higher with Fe amendments at either pH; a decoupling indicating that in this case ocean acidification did not increase Fe availability sufficiently to entirely satisfy the metabolic needs of the community. The differences between our findings and previous studies may stem from differences in the character of the dominant Fe-complexing ligands, which, in turn, suggests that future ocean acidification may create a mosaic of increasing and decreasing Fe availability in the N. Pacific.