Effects of Temperature on Phytoplankton Growth Rates

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Temperature is a fundamental variable controlling many processes in polar systems, but surprisingly few attempts to synthesize the effects of temperature on the growth of single-celled organisms called phytoplankton have been made. Because phytoplankton are the base of all marine food webs, they play an essential role in the ocean's ecology. Many global models use a simple relationship that extrapolate the effects of temperature on phytoplankton growth derived from warmer waters to polar temperatures, but this introduces substantial uncertainties in the models' results. This project will investigate the effects of temperature on growth at the low temperatures encountered in polar systems. Furthermore, given the potential oceanic changes expected in the future, it will allow much more accurate predictions of future responses to this change. The project will also further the NSF goals of training new generations of scientists and of making scientific discoveries available to the general public. The project will involve a graduate student in the fieldwork and undergraduates in research activities at the home institution. Results from the work will be incorporated into a new undergraduate course and the researchers will involve the public through general lectures and other outreach activities. Temperature is a fundamental variable in all ecosystems, and is the single most important delimiting feature of polar systems. It is also likely to be influenced by climate change; indeed, some (but not all) regions in the Antarctic have experienced significant atmospheric warming in the past half century. Despite the clear and profound influence of temperature of biological systems, nearly all models use a temperature-growth rate formulation derived from warmer temperatures. Modeled estimates of phytoplankton photosynthesis may underestimate these rates by up to 60% if the growth rate is underestimated by this temperature-phytoplankton growth relationship. If so, this could have profound impacts on regional and global models of the impacts of temperature change on oceanic productivity. To address this uncertainty, this project will quantify the phytoplankton maximum growth rate-temperature relationship at temperatures encountered in the Antarctic (less than 4 degrees C). Phytoplankton isolated from Antarctic waters will be used in experiments designed to assess the maximum growth rates of a number of types of phytoplankton that occur in the Antarctic. Temperature perturbation experiments will be performed to assess the response of Antarctic phytoplankton to a range of temperatures after having been acclimated to increased temperatures during growth.