1Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
2Biology Department, University of Southern California, Los Angeles, CA 90089-0371, USA
3Hollings Marine Laboratory, College of Charleston, Charleston, SC 29412, USA
4Department of Environmental Earth Systems Science, Stanford University, Stanford, CA 94305-2115, USA
5College of Marine Studies, University of Delaware, Lewes, DE 19958, USA
6School of Earth, Ocean and Environmental Sciences, University of Plymouth, Plymouth PL4 8AA, UK
7Virginia Institute of Marine Science, College of William and Mary, Gloucester Pt, VA 23602, USA
8Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, VA 23529, USA
Received: 30 May 2009 – Discussion started: 19 Jun 2009
Abstract. Iron availability and temperature are important limiting factors for the biota in many areas of the world ocean, and both have been predicted to change in future climate scenarios. However, the impacts of combined changes in these two key factors on microbial trophic dynamics and nutrient cycling are unknown. We examined the relative effects of iron addition (+1 nM) and increased temperature (+4°C) on plankton assemblages of the Ross Sea, Antarctica, a region characterized by annual algal blooms and an active microbial community. Increased iron and temperature individually had consistently significant but relatively minor positive effects on total phytoplankton abundance, phytoplankton and microzooplankton community composition, as well as photosynthetic parameters and nutrient drawdown. Unexpectedly, increased iron had a consistently negative impact on microzooplankton abundance, most likely a secondary response to changes in phytoplankton community composition. When iron and temperature were increased in concert, the resulting interactive effects were greatly magnified. This synergy between iron and temperature increases would not have been predictable by examining the effects of each variable individually. Our results suggest the possibility that if iron availability increases under future climate regimes, the impacts of predicted temperature increases on plankton assemblages in polar regions could be significantly enhanced. Such synergistic and antagonistic interactions between individual climate change variables highlight the importance of multivariate studies for marine global change experiments.
Revised: 14 Oct 2009 – Accepted: 11 Nov 2009 – Published: 21 Dec 2009
Rose, J. M., Feng, Y., DiTullio, G. R., Dunbar, R. B., Hare, C. E., Lee, P. A., Lohan, M., Long, M., W. O. Smith Jr., Sohst, B., Tozzi, S., Zhang, Y., and Hutchins, D. A.: Synergistic effects of iron and temperature on Antarctic phytoplankton and microzooplankton assemblages, Biogeosciences, 6, 3131-3147, doi:10.5194/bg-6-3131-2009, 2009.