Effects of Ocean Acidification on Nutrient Availability and Requirements in Phytoplankton

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The most certain effect on the ocean of the ongoing build up of atmospheric CO2 is an increase in the CO2 concentration, dissolved CO2 activity ([CO2]), and a decrease in the pH of surface waters. This "acidification" will likely affect the availability of nutrients to phytoplankton as well as the physiology of the organisms. Thus, from a biological point of view, the chemical changes in ocean chemistry brought about by the CO2 increase will interact with the physical changes, which are expected to modify the input of nutrients to the surface. The net effect on primary production and the export of organic matter to the deep represents a potential feedback to the increase in atmospheric CO2.In this project, researchers at Princeton University will quantify the effects of the ongoing increase in [CO2] and the decrease in pH in surface seawater on the requirements and availability of macro- and micro-nutrients in marine phytoplankton, and the resulting changes in the growth and elemental composition of the organisms. Based on what we know of the physiology of phytoplankton and some preliminary data, an increase in [CO2] likely to increase the efficiency with which the organisms utilize Fe and N, two of the principal limiting nutrients in the ocean. A decrease in pH is likely to change the availability of essential trace metals, particularly Fe, by changing their chemical speciation in the medium, and the uptake of macro-nutrients from organic sources by decreasing the activity of extracellular enzymes.To unravel the complex effects of ocean acidification on phytoplankton they will pursue initially three avenues of research based on three distinct hypotheses: 1) acidification lowers the rate of Fe uptake by phytoplankton cells and simultaneously increases their Fe use efficiency (the former because of low pH, the latter because of high [CO2]); 2) acidification increases the C:N ratio of N-limited phytoplankton because of an increase in N use efficiency and the storage of C-rich compounds; and 3) acidification decreases the ability of phytoplankton to use organic sources of P because of a decrease in the specific activity of alkaline phosphatase and in Zn availability for synthesis of the enzyme. The plan of work consists of mutually reinforcing laboratory and field experiments to test the various hypotheses and to elucidate the underlying biochemical mechanism so that the results can be extrapolated. Further work will depend on initial results. Broader Impacts: This project addresses an issue of great concern to society and the results of the research are thus expected to generate wide interest. Beyond the usual research and educational activities that are naturally embedded in such a project, a specific goal is to enhance scientific understanding and education more broadly within and outside the scientific community. Through multiple collaborations, this project will serve to bridge different communities interested in diverse aspects of the interactions between CO2 and marine phytoplankton-- from modelers and seagoing oceanographers to algal physiologists and biochemists. The topic of this project should also be effective for outreach activities designed to improve the education of science school teachers and provide them with material to enhance the effectiveness of their teaching. An internship program will provide hands-on research experience to students from community colleges in New Jersey.