Collaborative Research: Bloom Dynamics and Food-Web Structure in the Ross Sea: The Irradiance/Mixing Regime and Diatom Growith in Spring
The growing season for phytoplankton in polar oceans is short, but intense. There is an increasing body of evidence that in many Antarctic habitats, the most active period may be very early in the season, a period that has not been emphasized in previous investigations. This project is part of an interdisciplinary program that focuses on the dynamics of the spring phytoplankton bloom in a highly productive subsystem of the Antarctic, the Ross Sea. The overall program will test hypotheses related to the initiation of the phytoplankton bloom shortly after the onset of ice melt, the mechanisms controlling phytoplankton growth and productivity in spring, the implications and short-term fate of high productivity in spring, and the transition from spring to midsummer conditions. This component will test the closely related hypotheses that: (1) phytoplankton growth is controlled primarily by the relationship between solar irradiance and mixed-layer depth throughout the spring (2) diatom growth rates are much higher in spring than at any other time of year, in response to the more favorable irradiance/mixing relationships, and (3) persistence of diatom blooms in summer results from the diatoms' ability to outcompete other groups under the light-limited conditions that develop in turbid, high-biomass waters. These hypotheses will be tested by (1) obtaining the first reliable estimates of the Sverdrup "critical depth" in the Antarctic so that the changing relationship between the critical depth and the mixed- layer depth in spring can be defined, and (2) estimating diatom growth rates and the gross and net production attributable to diatoms throughout the spring. The results will provide information critical to an understanding of phytoplankton bloom dynamics in the Ross Sea.
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