Microbial community composition and growth dynamics in the Antarctic Polar Front and seasonal ice zone during late spring 1997

• Main Authors: Selph, Karen E., Landry, Michael R., Allen, Colleen B., Calbet, Albert, Christensen, Stephanie, Bidigare, Robert R.
• Other Authors: National Science Foundation (US)
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Pergamon Press 2001
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: http://hdl.handle.net/10261/180996; https://doi.org/10.1016/S0967-0645(01)00077-7; https://doi.org/10.13039/100000001

Special issue US Southern Ocean JGOFS Program (AESOPS) - Part II.-- 22 pages, 7 figures, 3 tables The microbial community between the Antarctic Polar Front region (APFr) and the seasonal ice edge at 170°W was examined as part of the US JGOFS AESOPS Process 1 Study during late spring (December) 1997. Water-mass identities of the sampled stations were determined based on physical properties, with three regions identified: the APFr, the South ACC region (SACCr), and the southern region of the ACC near the ice edge (SACCr-IE). The APFr (60.1-60.5°S) was dominated by centric diatoms, with mixed-layer communities tending toward single genera (i.e., Chaetoceros and Corethron). Stations in the SACCr (61.4-63.0°S) were also characterized by large centric diatoms, but no single genus dominated. In contrast, the SACCr-IE stations (64.1-64.4°S), positioned near the retreating ice edge, were dominated by colony-forming Phaeocystis. A seasonal succession in phytoplankton is proposed, with the youngest communities near the ice edge and the most >mature> in the polar front region. We found an inverse relationship between chlorophyll a values and phytoplankton growth rates. Phytoplankton growth rates were the highest (up to 1 d-1) in the APFr, despite relatively low chlorophyll a values. Microzooplankton grazing accounted for ∼50% of phytoplankton growth. The SACCr stations had intermediate chlorophyll a concentrations and phytoplankton growth rates (0.5-0.9 d-1), with grazing consuming ∼50-70% of growth. The SACCr-IE stations had the highest chlorophyll a values and the lowest phytoplankton growth rates (0.2 d-1) of the transect, while grazing accounted for ∼70% of growth in the one dilution experiment that gave a significant result. Given these growth and grazing estimates, a higher proportion of production in the northern diatom-dominated regions was available for export than in the Phaeocystis-dominated ice edge stations. However, since microzooplankton produce small fecal debris, the bulk of the consumed production ...