Controls on iron availability to marine phytoplankton

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Anthropogenic greenhouse gas emissions such as carbon dioxide (CO2) are causing climate change, global warming, and ocean acidification. Microscopic plants called phytoplankton, living in the surface oceans, sequester 50% of global CO2 and supply >50% of new nitrogen used for primary production. Other than light and major nutrients, phytoplankton growth is strongly influenced by availability of the metal iron (Fe), because the metal is essential for photosynthesis and nitrogen fixation, but is very scarce in the open ocean. Iron is so important that seeding the metal into Fe-poor areas has been proposed as a viable method for controlling climate change by enhancing bio-uptake of atmospheric CO2 by phytoplankton. In order to understand how Fe controls atmospheric CO2 levels and oceanic productivity, it is important to first attempt to understand the controls on availability of the metal to marine phytoplankton. The prevailing view is that metal bioavailability depends upon its chemical forms (i.e., metal speciation) in ambient bulk waters; however, data from our recent studies are inconsistent with the long-standing paradigm. In the proposed project, I will challenge this long-standing paradigm by studying the Fe speciation in the phycosphere, a micrometer scale space which directly surrounds a phytoplankton cell, through the use of novel nano-technologies and inter-disciplinary approaches. Phytoplankton directly take up nutrients including Fe from the phycosphere, rather than directly from bulk seawater, however the Fe speciation in this micro-scale space has not previously been studied. The lack of knowledge on phycosphere Fe speciation would potentially result in serious under or overestimation of oceanic Fe availability in current and future oceans, and lead to erroneous prediction of how ocean ecosystem responds to Climate Change. The interdisciplinary project will provide a new view on the fundamental processes in Fe acquisition by phytoplankton, and it will certainly help improve the capability and accuracy of international agencies such as the Intergovernmental Panel on Climate Change to assess the sensitivity of planetary system to Climate Change.