Phytoplankton community structure and stocks in the Southern Ocean (30–80°E) determined by CHEMTAX analysis of HPLC pigment signatures

摘要: Abstract The geographic distribution, stocks and vertical profiles of phytoplankton the seasonal ice zone off east Antarctica were determined during 2005–2006 austral summer Baseline Research on Oceanography, Krill Environment-West (BROKE-West) survey. CHEMTAX analysis HPLC pigment samples, coupled with microscopy, permitted a detailed survey along seven transects covering an extensive area between 30°E 80°E, from 62°S to coast. Significant differences found in composition populations separated by Southern Boundary Antarctic Circumpolar Current (SB), as well small influence Weddell Gyre western sector ‘zone south Current’ (SACCZ). Within SACCZ, we identified primary bloom under ice, secondary near edge, open-ocean deep population. similarity distribution patterns across all allowed us generalise hypothesized sequence for season. bloom, Chl up 239 mg m−2, occurred about 35 days before complete disappearance sea contained both cells water column those released melting ice. These blooms composed haptophytes (in particular, colonies gametes Phaeocystis antarctica), diatoms cryptophytes (or cryptophyte symbiont-containing ciliate Myrionecta rubrum). Aggregates quickly sank upper declined 56–92 mg m−2, but and, lesser extent, continued until 20 after melt. coincided sharp increase P. antarctica grazing, indicated increasing phaeophytin phaeophorbide a. Chlorophyllide content suggests that diatom then senesced, probably due iron exhaustion. Stocks rapidly declined, apparently grazing krill moved southward following retreating We suggest export faecal pellets stripped (as suggested low Fv/Fm ratios Haptophytes – was not measured). Thus, possibly sedimentation, created migrating gradient, limiting growth column. North postulated nanoflagellate community developed at depth, 36–49 mg m−2. This based regenerated production, sustained residual and/or upwelling iron, close correspondence distributions Fv/Fm. consisted (chiefly gametes), dinoflagellates, prasinophytes, cryptophytes, some diatoms. Selective may have fashioned maintained community. SB, ranged 40–67 mg m−2 predominantly mixed layer, remained low, suggesting iron-limited. interpretations provide cogent explanation structure late microbial marginal zone.