Acquisition of Moored Water Sampling Equipment to Assess the Regulation of Phytoplankton Productivity in the Ross Sea

点击翻译按钮获取中文摘要

During the past few decades of oceanographic research, oceanographers have observed significant interannual variations in physical, biological, chemical and geological processes. The best-known example is the ENSO phenomenon in the equatorial Pacific. Interannual variations in the Southern Ocean are also known to occur in ice extent and concentration, in the composition of herbivore communities, and in bird and marine mammal distributions and reproductive success. Yet little is known about the interannual variations in production of phytoplankton or the role that these variations play in the food web. Furthermore, nothing is known concerning the potential interannual variations in the controls of phytoplankton production. This proposal seeks funds to augment a presently funded project which examines interannual variability in the Ross Sea and to collect time-series data on variables influencing the seasonal production of phytoplankton in the southern Ross Sea, Antarctica. This project will involve adding three instruments each to two independent oceanographic moorings in order to develop a mooring system capable of providing data to address the issue of interannual variability in the Ross Sea ecosystem. These new instruments include a fast repetition rate fluorometer, a whole water sampler, and an in situ silicic acid analyzer. These instruments will allow for the determination of the timing and extent of iron limitation (using an assessment of photochemical efficiency, which is a sensitive index of iron limitation), the measurement of dissolved silicate uptake rates to assess the role of diatoms in the southern Ross Sea, and the microscopic determination of the composition of the phytoplankton assemblage. Thus, insights will be obtained into the biological changes that occur continuously in such a rapidly changing, non-equilibrium environment. Furthermore, it will assess the interannual variations of the production of the two major functional groups of the system, diatoms and Phaeocystis antarctica, a colonial haptophyte. The new instruments will be added to two existing taut-line moorings with in situ nitrate analyzers moored in the surface mixed layer. These will collect for the first time in the Antarctic a time-series of euphotic zone nutrient concentrations over the late spring-summer period. By integrating the new instruments into the mooring systems, information on the period of transition between irradiance limitation and iron limitation will be obtained. Additional data from the new instruments will allow for a detailed temporal record of the role of diatoms in this region. Diatoms are critical, as they are considered to be the major talon contributing to the effect transfer of energy and organic matter through the Antarctic food web as well as significantly contributing to the vertical flux of biogenic matter to the sediments. Interannual variations of production are potentially significant the growth and survival of higher trophic levels of the Ross Sea. They are also important in order to understand the natural variability in biogeochemical processes of the region. Because polar regions such as the Ross Sea are predicted to be impacted by future climate change, biological changes are also anticipated. Placing these changes in the context of natural variability is an essential element of understanding and predicting such alterations.