Karen Westwood, Rick Van den Enden, and Sarah Ugalde
Low irradiance during Antarctic winter presents a serious challenge to phytoplankton which rely on sunlight for photosynthesis. Pelagic populations are reduced to very low levels in the water column while some may overwinter in the sea-ice along with specialist ice-algae. This program will study the composition and productivity of phytoplankton and bacteria during early spring to determine the species composition and productivity.
The program will have several components:
Underway surface transect: Samples will be collected from the ship’s clean seawater line at regular intervals during the outward and return transects to determine the species composition, concentrations of chlorophyll and other pigments, and counts of coccolithophorids. This is part of our ongoing monitoring program (with some 60 transects to date) to determine seasonal patterns of phytoplankton as a basis for detection of long-term change.
Primary productivity: Photosynthesis by phytoplankton will be measured at 6 depths at each CTD station using 14C incorporation in samples incubated with a range of irradiances. Primary production rates will be calculated using photosynthetic rates over depth and time. The data will also be used to validate Fast Repetition Rate Fluorometry (FRRF) measurements made by Robert Johnson.
Productivity of sea ice algae: will also be measured using 14C incorporation methods in macerated ice cores. This work will focus on the amount of production transferred into extracellular organic products, particularly polysaccharides, to determine how the algae alter their local environment in the ice to enhance their survival. Viscosity of seawater and ice brine will be measured as part of this study.
Bacterial productivity and composition: Production by bacteria will be measured by incorporation of 14C leucine. Bacterial DNA will be collected to determine the taxa present. The data will complement measurements of extracellular polysaccharides which are thought to provide a carbon source for bacterial growth.
Culture experiments (in collaboration with McMinn group): Samples of ice cores and seawater will be incubated in sterile seawater for several weeks to determine which species develop. This will provide an indication of the importance of sea-ice for seeding the spring-summer ice edge bloom. Cultures of phytoplankton will be returned to Australia for studies of their physiology and as part of our ongoing program to develop molecular markers and determine pigment composition of key taxa.
Other measurements: Samples will also be preserved for light and electron microscopic identification of phytoplankton species. We will also be conducting analyses of pigments (chlorophylls and carotenoids), particulate organic carbon and nitrogen, dissolved inorganic carbon and dissolved nutrients (N, P, Si).